QR56 
 C76s 
 
 Southern Branch 
 of the 
 
 University of California 
 
 Los Angeles 
 
 Form L-l
 
 This book is DUE on the last date stamded below 
 
 m-g 
 
 1 5 1933 
 APR 2 7 1934 
 
 J rjtfi, 
 MAY 1 9 193b 
 
 MAR 6 -1958 
 
 Form L-9-5m-7,'22 

 
 VARIOUS KINDS OF BACTERIA. 
 
 . To the left the common hay bacillus (Bacillus subtilis) to the right a Spirit 
 lum. B. A Coccus form (Planococcus\ C, D, E. Species of Pseudomonas. 
 f, G. Species of Bacillus. F being that of typhoid fever. H. Microspira. 
 /, A", Z, M. Species of Spirillum. (After Engler and Prantl.)
 
 THE STORY OF 
 GERM LIFE 
 
 BY 
 
 H. W. CONN 
 
 PROFESSOR OF BIOLOGY AT WESLEYAN UNIVERSITY, 
 
 AUTHOR OF EVOLUTION OF TO-DAY, 
 
 THE LIVING WORLD, ETC. 
 
 WITH ILLUSTRATIONS 
 
 NEW YORK 
 MCMXII
 
 COPYRIGHT, 1897, 
 Bv D. APPLETON AND COMPANY. 
 
 *' '' ' Prihfecf ftf the "United States* o! America
 
 PREFACE. 
 
 (P THE rapid progress of discovery in the last 
 few years has created a very general interest in 
 
 ^~ bacteria. Few people who read could be found 
 to-day who have not some little idea of these 
 organisms and their relation to disease. It is, 
 
 \* however, unfortunately a fact that it is only their 
 relation to disease which has been impressed upon 
 O the public. The very word bacteria, or microbe, 
 - conveys to most people an idea of evil. The last 
 few years have above all things emphasized the 
 j importance of these organisms in many relations 
 ( entirely independent of disease, but this side of 
 j the subject has not yet attracted very general 
 attention, nor does it yet appeal to the reader 
 with any special force. It is the purpose of the 
 following pages to give a brief outline of our 
 
 r\ knowledge of bacteria and their importance in 
 
 \ | the world, including not only their well-known 
 agency in causing disease, but their even greater 
 importance as agents in other natural phenomena, 
 It is hoped that the result may be to show that 
 these organisms are to be regarded not primarily 
 in the light of enemies, but as friends, and thus 
 to correct some of the very general but erroneous 
 ideas concerning their relation to our life. 
 
 MIDDLETOWN, April i, 1897. 
 3
 
 CONTENTS. 
 
 CHAPTER PACK 
 
 I. BACTERIA AS PLANTS 9 
 
 Historical. Form of bacteria. Multiplication of bac- 
 teria. Spore formation. Motion. Internal structure. 
 Animals or plants ? Classification. Variation. Where 
 bacteria are found. 
 
 II. MISCELLANEOUS USES OF BACTERIA IN THE ARTS. 41 
 
 Maceration industries. Linen. Jute. Hemp. 
 Sponges. Leather. Fermentative industries. Vine- 
 gar. Lactic acid. Butyric acid. Bacteria in tobacco 
 curing. Troublesome fermentations. 
 
 III. BACTERIA IN THE DAIRY 66 
 
 Sources of bacteria in milk. Effect of bacteria on 
 milk. Bacteria used in butter making. Bacteria in 
 cheese making. 
 
 IV. BACTERIA IN NATURAL PROCESSES . . .94 
 
 Bacteria as scavengers. Bacteria as agents in Nature's 
 food cycle. Relation of bacteria to agriculture. Sprout- 
 ing of seeds. The silo. The fertility of the soil. Bac- 
 teria as sources of trouble to the farmer. Coal forma- 
 tion. 
 
 V. PARASITIC BACTERIA AND THEIR RELATION TO 
 
 DISEASE 128 
 
 Method of producing disease. Pathogenic germs not 
 strictly parasitic. Pathogenic germs that are true para- 
 sites. What diseases are due to bacteria. Variability
 
 6 THE STORY OF GERM LIFE. 
 
 CHAPTER PACK 
 
 of pathogenic powers. Susceptibility of the individual. 
 Recovery from bacteriological diseases. Diseases 
 caused by organisms other than bacteria. 
 
 VI. METHODS OF COMBATING PARASITIC BACTERIA . 165 
 
 Preventive medicine. Bacteria in surgery. Preven- 
 tion by inoculation. Limits of preventive medicine. 
 Curative medicine. -Drugs. Vis medicatrix naturae. 
 Antitoxines and their use. Conclusion.
 
 LIST OF ILLUSTRATIONS. 
 
 FIGURE FACE 
 
 Various kinds of bacteria . . . Frontispiece 
 
 1. General shapes of bacteria 18 
 
 2. Method of multiplication of bacteria. ... 19 
 
 3. Micrococci 19 
 
 4. Streptococci 19 
 
 5. Sarcina 2O 
 
 6. Separate rods showing variations in size ... 20 
 
 7. Rod-forms united to form chains .... 20 
 
 8. Various types of spiral bacteria 21 
 
 9. Various shaped rods 23 
 
 10. Bacteria surrounded by capsules .... 23 
 
 11. Various types of bacteria "colonies" ... 24 
 
 12. Endogenous spores 26 
 
 13. So-called arthrogenous spores 27 
 
 14. Formation of spores in unusual forms (Crenothrix) . 28 
 
 15. Bacteria provided with flagella 29 
 
 16. Internal structure of bacteria 30 
 
 17. Threads of Oscillaria 32 
 
 1 8. Bacillus acetieum, of vinegar ..... 53 
 
 19. Bacillus acidi lactici, of sour milk . . . . 7 1 
 
 20. Dairy bacterium producing red milk .... 73 
 
 21. Dairy bacterium producing pleasant flavours in butter 80 
 
 22. Dairy bacterium producing pleasant aroma in butter 81 
 
 23. Dairy bacterium producing pleasant flavour in butter 83 
 
 24. Dairy bacterium producing " swelled " cheese . . 92 
 
 25. Diagram illustrating Nature's food cycle ... 99 
 
 7
 
 8 LIST OF ILLUSTRATIONS. 
 
 FIGURE PAGE 
 
 26. Soil bacteria which produce nitrification . . . 103 
 
 27. Soil bacteria which produce tubercles on the toots of 
 
 legumes IO8 
 
 28. Diphtheria bacillus 134 
 
 29. Tetanus bacillus 135 
 
 30. Typhoid bacillus ....... 136 
 
 31. Tuberculosis bacillus 137 
 
 32. Anthrax bacillus 138 
 
 33. White blood corpuscles and other phagocytes . . 152 
 
 34. Malarial organism 161
 
 THE STORY OF GERM LIFE. 
 
 CHAPTER I. 
 
 BACTERIA AS PLANTS. 
 
 DURING the last fifteen years the subject of 
 bacteriology* has developed with a marvellous 
 rapidity. At the beginning of the ninth decade 
 of the century bacteria were scarcely heard of 
 outside of scientific circles, and very little was 
 known about them even among scientists. To- 
 day they are almost household words, and every- 
 one who reads is beginning to recognise that 
 they have important relations to his everyday 
 life. The organisms called bacteria comprise 
 simply a small class of low plants, but this small 
 group has proved to be of such vast importance 
 in its relation to the world in general that its 
 study has little by little crystallized into a science 
 by itself. It is a somewhat anomalous fact that 
 a special branch of science, interesting such a 
 large number of people, should be developed 
 around a small group of low plants. The impor- 
 tance of bacteriology is not due to any importance 
 bacteria have as plants or as members of the 
 vegetable kingdom, but solely to their powers of 
 
 * The term microbe is simply a word which has been 
 coined to include all of the microscopic plants commonly in- 
 cluded under the terms bacteria and yeasts. 
 9
 
 10 THE STORY OF GERM LIFE. 
 
 producing profound changes in Nature. There is 
 no one family of plants that begins to compare 
 with them in importance. It is the object of this 
 work to point out briefly how much both of good 
 and ill we owe to the life and growth of these 
 microscopic organisms. As we have learned 
 more and more of them during the last fifty years, 
 it has become more and more evident that this 
 one little class of microscopic plants fills a place 
 in Nature's processes which in some respects bal- 
 ances that filled by the whole of the green plants. 
 Minute as they are, their importance can hardly 
 be overrated, for upon their activities is founded 
 the continued life of the animal and vegetable 
 kingdom. For good and for ill they are agents 
 of neverceasing and almost unlimited powers. 
 
 HISTORICAL. 
 
 The study of bacteria practically began with 
 the use of the microscope. It was toward the 
 close of the seventeenth century that the Dutch 
 microscopist, Leeuwenhoek, working with his sim- 
 ple lenses, first saw the organisms which we now 
 know under this name, with sufficient clearness 
 to describe them. Beyond mentioning their ex- 
 istence, however, his observations told little or 
 nothing. Nor can much more be said of the stud- 
 ies which followed during the next one hundred 
 and fifty years. During this long period many a 
 microscope was turned to the observation of these 
 minute organisms, but the majority of observers 
 were contented with simply seeing them, marvel- 
 ling at their minuteness, and uttering many excla- 
 mations of astonishment at *he wonders of Nature. 
 A few men of more strictly scientific natures paid
 
 BACTERIA AS PLANTS. II 
 
 some attention to these little organisms. Among 
 them we should perhaps mention Von Gleichen, 
 Miiller, Spallanzani, and Needham. Each of 
 these, as well as others, made some contributions 
 to our knowledge of microscopical life, and among 
 other organisms studied those which we now call 
 bacteria. Speculations were even made at these 
 early dates of the possible causal connection of 
 these organisms with diseases, and for a little the 
 medical profession was interested in the sugges- 
 tion. It was impossible then, however, to obtain 
 any evidence for the truth of this speculation, and 
 it was abandoned as unfounded, and even forgot- 
 ten completely, until revived again about the mid- 
 dle of the ipth century. During this century 
 of wonder a sufficiency of exactness was, how- 
 ever, introduced into the study of microscopic or- 
 ganisms to call for the use of names, and we find 
 Miiller using the names of Monas, Proteus, Vibrio, 
 Bacillus, and Spirillum, names which still continue 
 in use, although commonly with a different signifi- 
 cance from that given them by Miiller. Miiller 
 did indeed make a study sufficient to recognise 
 the several distinct types, and attempted to clas- 
 sify these bodies. They were not regarded as of 
 much importance, but simply as the most minute 
 organisms known. 
 
 Nothing of importance came from this work, 
 however, partly because of the inadequacy of the 
 microscopes of the day, and partly because of a 
 failure to understand the real problems at issue. 
 When we remember the minuteness of the bacteria, 
 the impossibility of studying any one of them for 
 more than a few moments at a time only so long, 
 in fact, as it can be followed under a microscope; 
 when we remember, too, the imperfection of the
 
 12 THE STORY OF GERM LIFE. 
 
 compound microscopes which made high powers 
 practical impossibilities ; and, above all, when we 
 appreciate the looseness of the ideas which per- 
 vaded all scientists as to the necessity of accurate 
 observation in distinction from inference, it is not 
 strange that the last century gave us no knowl- 
 edge of bacteria beyond the mere fact of the ex- 
 istence of some extremely minute organisms in 
 different decaying materials. Nor did the igth 
 century add much to this until toward its middle. 
 It is true that the microscope was vastly improved 
 early in the century, and since this improvement 
 served as a decided stimulus to the study of mi- 
 croscopic life, among other organisms studied, 
 bacteria received some attention. Ehrenberg, 
 Dujardin, Fuchs, Perty, and others left the im- 
 press of their work upon bacteriology even before 
 the middle of the century. It is true that Schwann 
 shrewdly drew conclusions as to the relation of 
 microscopic organisms to various processes of 
 fermentation and decay conclusions which, al- 
 though not accepted at the time, have subse- 
 quently proved to be correct. It is true that 
 Fuchs made a careful study of the infection of 
 " blue milk," reaching the correct conclusion that 
 the infection was caused by a microscopic organ- 
 ism which he discovered and carefully studied. 
 It is true that Henle made a general theory as to 
 the relation of such organisms to diseases, and 
 pointed out the logically necessary steps in a dem- 
 onstration of the causal connection between any 
 organism and a disease. It is true also that a 
 general theory of the production of all kinds of 
 fermentation by living organisms had been ad- 
 vanced. But all these suggestions made little 
 impression. On the one hand, bacteria were not
 
 BACTERIA AS PLANTS. 13 
 
 recognised as a class of organisms by themselves 
 were not, indeed, distinguished from yeasts or 
 other minute animalculae. Their variety was not 
 mistrusted and their significance not conceived. 
 As microscopic organisms, there were no reasons 
 for considering them of any more importance 
 than any other small animals or plants, and their 
 extreme minuteness and simplicity made them of 
 little interest to the microscopist. On the other 
 hand, their causal connection with fermentative 
 and putrefactive processes was entirely obscured 
 by the overshadowing weight of the chemist Lie- 
 big, who believed that fermentations and putre- 
 factions were simply chemical processes. Liebig 
 insisted that all albuminoid bodies were in a 
 state of chemically unstable equilibrium, and if 
 left to themselves would fall to pieces without 
 any need of the action of microscopic organisms. 
 The force of Liebig's authority and the brilliancy 
 of his expositions led to the wide acceptance of 
 his views and the temporary obscurity of the re- 
 lation of microscopic organisms to fermentative 
 and putrefactive processes. The objections to 
 Liebig's views were hardly noticed, and the force 
 of the experiments of Schwann was silently ig- 
 nored. Until the sixth decade of the century, 
 therefore, these organisms, which have since be- 
 come the basis of a new branch of science, had 
 hardly emerged from obscurity. A few micros- 
 copists recognised their existence, just as they 
 did any other group of small animals or plants, 
 but even yet they failed to look upon them as 
 forming a distinct group. A growing number of 
 observations was accumulating, pointing toward 
 a probable causal connection between fermenta- 
 tive and putrefactive processes and the growth of 
 2
 
 14 THE STORY OF GERM LIFE. 
 
 microscopic organisms; but these observations 
 were known only to a few, and were ignored by 
 the majority of scientists. 
 
 It was Louis Pasteur who brought bacteria to 
 the front, and it was by his labours that these or- 
 ganisms were rescued from the obscurity of scien- 
 tific publications and made objects of general and 
 crowning interest. It was Pasteur who first suc- 
 cessfully combated the chemical theory of fer- 
 mentation by showing that albuminous matter 
 had no inherent tendency to decomposition. It 
 was Pasteur who first clearly demonstrated that 
 these little bodies, like all larger animals and 
 plants, come into existence only by ordinary 
 methods of reproduction, and not by any sponta- 
 neous generation, as had been earlier claimed. 
 It was Pasteur who first proved that such a com- 
 mon phenomenon as. the souring of milk was pro- 
 duced by microscopic organisms growing in the 
 milk. It was Pasteur who first succeeded in dem- 
 onstrating that certain species of microscopic or- 
 ganisms are the cause of certain diseases, and in 
 suggesting successful methods of avoiding them. 
 All these discoveries were made in rapid succes- 
 sion. Within ten years of the time that his name 
 began to be heard in this connection by scien- 
 tists, the subject had advanced so rapidly that 
 it had become evident that here was a new 
 subject of importance to the scientific world, if 
 not to the public at large. The other important 
 discoveries which Pasteur made it is not our pur- 
 pose to mention here. His claim to be consid- 
 ered the founder of bacteriology will be recog- 
 nised from what has already been mentioned. 
 It was not that he first discovered the organisms, 
 or first studied them ; it was not that he first sug-
 
 BACTERIA AS PLANTS. 15 
 
 gested their causal connection with fermentation 
 and disease, but it was because he for the first time 
 placed the subject upon a firm foundation by prov- 
 ing with rigid experiment some of the suggestions 
 made by others, and in this way turned the atten- 
 tion of science to the study of micro-organisms. 
 
 After the importance of the subject had been 
 demonstrated by Pasteur, others turned their at- 
 tention in the same direction, either for the pur- 
 pose of verification or refutation of Pasteur's 
 views. The advance was not very rapid, however, 
 since bacteriological experimentation proved to be 
 a subject of extraordinary difficulty. Bacteria 
 were not even yet recognised as a group of organ- 
 isms distinct enough to be grouped by themselves, 
 but were even by Pasteur at first confounded with 
 yeasts. As a distinct group of organisms they 
 were first distinguished by Hoffman in 1869, since 
 which date the term bacteria, as applying to this 
 special group of organisms, has been coming 
 more and more into use. So difficult were the 
 investigations, that for years there were hardly 
 any investigators besides Pasteur who could suc- 
 cessfully handle the subject and reach conclu- 
 sions which could stand the test of time. For the 
 next thirty, years, although investigators and in- 
 vestigations continued to increase, we can find 
 little besides dispute and confusion along this 
 line. The difficulty of obtaining for experiment 
 any one kind of bacteria by itself, unmixed with 
 others (pure cultures), rendered advance almost 
 impossible. So conflicting were the results that 
 the whole subject soon came into almost hopeless 
 confusion, and very few steps were taken upon 
 any sure basis. So difficult were the methods, so 
 contradictory and confusing the results, because
 
 10 THE STORY OF GERM LIFE. 
 
 of impure cultures, that a student of to-day who 
 wishes to look up the previous discoveries in 
 almost any line of bacteriology need hardly go 
 back of 1880, since he can almost rest assured 
 that anything done earlier than that was more 
 likely to be erroneous than correct. 
 
 The last fifteen years have, however, seen a 
 wonderful change. The difficulties had been 
 mostly those of methods of work, and with the 
 ninth decade of the century these methods were 
 simplified by Robert Koch. This simplification 
 of method for the first time placed this line of 
 investigation within the reach of scientists who 
 did not have the genius of Pasteur. It was now 
 possible to get pure cultures easily, and to obtain 
 with such pure cultures results which were uni- 
 form and simple. It was now possible to take 
 steps which had the stamp of accuracy upon 
 them, and which further experiment did not dis- 
 prove. From the time when these methods were 
 thus made manageable the study of bacteria in- 
 creased with a rapidity which has been fairly 
 startling, and the information which has accumu- 
 lated is almost formidable. The very rapidity 
 with which the investigations have progressed 
 has brought considerable confusion, from the fact 
 that the new discoveries have not had time to 
 be properly assimilated into knowledge. To- 
 day many facts are known whose significance is 
 still uncertain, and a clear logical discussion of 
 the facts of modern bacteriology is not possible. 
 But sufficient knowledge has been accumulated and 
 digested to show us at least the direction along 
 which bacteriological advance is tending, and it 
 is to the pointing out of these directions that the 
 following pages will be devoted.
 
 BACTERIA AS PLANTS. 1 7 
 
 WHAT ARE BACTERIA ? 
 
 The most interesting facts connected with the 
 subject of bacteriology concern the powers and 
 influence in Nature possessed by the bacteria. 
 The morphological side of the subject is interest- 
 ing enough to the scientist, but to him alone. 
 Still, it is impossible to attempt to study the 
 powers of bacteria without knowing something of 
 the organisms themselves. To understand how 
 they come to play an important part in Nature's 
 processes, we must know first how they look and 
 where they are found. A short consideration of 
 certain morphological facts will therefore be 
 necessary at the start. 
 
 FORM OF BACTERIA. 
 
 In shape bacteria are the simplest conceivable 
 structures. Although there are hundreds of dif- 
 ferent species, they have only three general forms, 
 which have been aptly compared to billiard balls, 
 lead pencils, and corkscrews. Spheres, rods, and 
 spirals represent all shapes. The spheres may be 
 large or small, and may group themselves in va- 
 rious ways; the rods may be long or short, thick 
 or slender; the spirals may be loosely or tightly 
 coiled, and may have only one or two or may 
 have many coils, and they may be flexible or 
 stiff ; but still rods, spheres, and spirals comprise 
 all types (Fig. i). 
 
 In size there is some variation, though not 
 very great. All are extremely minute, and never 
 visible to the naked eye. The spheres vary from 
 0.25 /i to 1.5 /A (0.000012 to 0.00006 inches). The 
 rods may be no more than 0.3 p in diameter, 
 or may be as wide as 1.5 /* to 2.5 /*, and in length
 
 i8 
 
 THE STORY OF GERM LIFE. 
 
 vary all the way from a length scarcely longer 
 than their diameter to long threads. About the 
 same may be said of the spi- 
 ral forms. They are decid- 
 edly the smallest living or- 
 ganisms which our micro- 
 scopes have revealed. 
 
 In their method of grcnvth 
 we find one of the most char- 
 acteristic features. They 
 universally have the power 
 of multiplication by simple 
 division or fission. Each in- 
 dividual elongates and then 
 divides in the middle into 
 FIG. i.-GeneraT shapes tw similar halves, each of 
 of bacteria: a, Spheri- which then repeats the pro- 
 cai forms ; b, Rod- ces s. This method of mul- 
 rKms? 1 31 c ' Sp " tiplication by simple division 
 is the distinguishing mark 
 
 which separates the bacteria from the yeasts, the 
 latter plants multiplying by a process known as 
 budding. Fig. 2 shows these two methods of 
 multiplication. 
 
 While all bacteria thus multiply by division, 
 certain differences in the details produce rather 
 striking differences in the results. Considering 
 first the spherical forms, we find that some species 
 divide, as described, into two, which separate at 
 once, and each of which in turn divides in the op- 
 posite direction, called Micrococcus, (Fig. 3). Other 
 species divide only in one direction. Frequently 
 they do not separate after dividing, but remain 
 attached. Each, however, again elongates and di- 
 vides again, but all still remain attached. There 
 are thus formed long chains of spheres like strings
 
 BACTERIA AS PLANTS. 
 
 of beads, called Streptococci (Fig. 4). Other species 
 divide first in one direction, then at right angles 
 to the first division, and a third division follows at 
 right angles to 
 the plane of 
 the first two, 
 thus producing 
 solid groups of 
 fours, eights, 
 or sixteens 
 (Fig. 5), called 
 Sarcina. Each 
 different spe- 
 cies of bacteria 
 is uniform in 
 its method of 
 
 division, and HI 
 
 these differen- 
 ces are there- 
 fore indica- 
 tions of differ- 
 ences in spe- 
 cies, or, according to our present method of 
 classification, the different methods of division 
 
 FIG. 2. Method of multiplication of bacte- 
 ria : a and b, Bacteria dividing by fis- 
 sion ; c, A yeast multiplying by budding. 
 
 FIG. 3. Micrococci. 
 
 FIG. 4. Streptococci. 
 
 represent different genera. All bacteria produ- 
 cing Streptococcus chains form a single genus Strep*
 
 20 THE STORY OF GERM LIFE. 
 
 tococcus, and all which divide in three division 
 planes form another genus, Sarcina, etc. 
 
 FIG. 5. Sarcina. 
 
 FIG. 6. Separate rods 
 showing variations in 
 size, magnified about 
 looo diameters. 
 
 The rod-shaped bacteria also differ somewhat, 
 but to a less extent. They almost always divide 
 in a plane at right angles to their longest dimen- 
 sion. But here again we find some species sepa- 
 rating immediately after division, and thus always 
 appearing as short rods (Fig. 6), while others 
 
 remain attached 
 after division 
 and form long 
 chains. Some- 
 times they ap- 
 pear to continue 
 to increase in 
 length without 
 showing any 
 signs of divis- 
 
 FIG. 7. Rod-forms united to form chains, ion, and in this 
 
 way long threads 
 
 are formed (Fig. 7). These threads are, however, 
 potentially at least, long chains of short rods, and 
 under proper conditions they will break up into 
 such short rods, as shown in Fig. 7 a. Occasion- 
 ally a rod species may divide lengthwise, but this 
 is rare. Exactly the same may be said of the
 
 BACTERIA AS PLANTS. 
 
 spiral forms. Here, too, we find short rods and 
 long chains, or long spiral filaments in which can 
 be seen no division 
 into shorter elements, 
 but which, under cer- 
 tain conditions, break 
 up into short sections 
 (Fig. 8). 
 
 RAPIDITY OF 
 MULTIPLICATION. 
 
 It is this power of 
 multiplication by di- 
 vision that makes bac- 
 teria agents of such 
 significance. Their 
 minute size would 
 make them harmless 
 enough if it were not 
 for an extraordinary 
 power of multiplica- 
 tion. This power of 
 growth and division 
 is almost incredible. 
 Some of the species 
 which have been care- 
 fully watched under 
 
 the microscope have been found under favourable 
 conditions to grow so rapidly as to divide every 
 half hour, or even less. The number of offspring 
 that would result in the course of twenty-four 
 hours at this rate is of course easily computed. 
 In one day each bacterium would produce over 
 16,500,000 descendants, and in two days about 
 281,500,000,000. It has been further calculated 
 
 3. Various types of spiral 
 bacteria.
 
 22 THE STORY OF GERM LIFE. 
 
 that these 281,500,000,000 would form about a 
 solid pint of bacteria and weigh about a pound. 
 At the end of the third day the total descendants 
 would amount to 47,000,000,000,000, and would 
 weigh about 16,000,000 pounds. Of course these 
 numbers have no significance, for they are never 
 actual or even possible numbers. Long before 
 the offspring reach even into the millions their 
 rate of multiplication is checked either by lack of 
 food or by the accumulation of their own ex- 
 creted products, which are injurious to them. But 
 the figures do have interest since they show faint- 
 ly what an unlimited power of multiplication these 
 organisms have, and thus show us that in dealing 
 with bacteria we are dealing with forces of al- 
 most infinite extent. 
 
 This wonderful power of growth is chiefly due 
 to the fact that bacteria feed upon food which is 
 highly organized and already in condition for ab- 
 sorption. Most plants must manufacture their 
 own foods out of simpler substances, like carbonic 
 dioxide (CO 2 ) and water, but bacteria, as a rule, 
 feed upon complex organic material already pre- 
 pared by the previous life of plants or animals. 
 For this reason they can grow faster than other 
 plants. Not being obliged to make their own 
 foods like most plants, nor to search for it like 
 animals, but living in its midst, their rapidity of 
 growth and multiplication is limited only by their 
 power to seize and assimilate this food. As they 
 grow in such masses of food, they cause certain 
 chemical changes to take place in it, changes 
 doubtless directly connected with their use of the 
 material as food. Recognising that they do 
 cause chemical changes in food material, and re- 
 membering this marvellous power of growth, we
 
 BACTERIA AS PLANTS. 
 
 are prepared to believe them capable of producing 
 changes wherever they get a foothold and begin 
 to grow. Their power of feeding upon com- 
 plex organic food 
 and producing chemi- 
 cal changes therein, 
 together with their 
 marvellous power of 
 assimilating this ma- 
 terial as food, make 
 them agents in Na- 
 
 ture of extreme 
 portance. 
 
 FIG. 9. Showing various shaped 
 rods. 
 
 DIFFERENCES BETWEEN DIFFERENT SPECIES OF 
 BACTERIA. 
 
 While bacteria are thus very simple in form, 
 there are a few 
 other slight varia- 
 tions in detail 
 which assist in dis- 
 a tinguishing them. 
 The rods are some- 
 times very blunt at 
 the ends, almost 
 as if cut square 
 across, while in 
 other species they 
 are more rounded 
 and occasionally 
 slightly tapering 
 (Fig. 9). Some- 
 times they are sur- 
 
 d, Bacteria showing the supposed roun d e d t)V a thin 
 structure in which x is the nucleus, , 
 
 and v the protoplasm. layer of some gelat- 
 
 FIG. 10. Bacteria surrounded by cap- 
 sules : a and b represent zoogloea ; 
 c, Chains of cocci with a capsule ;
 
 THE STORY OF GERM LIFE. 
 
 inous substance, which forms what is called a 
 capsule (Fig. 10). This capsule may connect them 
 and serve as a cement, to prevent the separate 
 elements of a chain from falling apart (Fig. 10 c). 
 
 Sometimes such 
 a gelatinous se- 
 cretion will unite 
 great masses of 
 bacteria into 
 clusters, which 
 may float on the 
 surface of the 
 liquid in which 
 they grow or 
 may sink to the 
 bottom. Such 
 masses are called 
 zooglcea, and their 
 general appear- 
 ance serves as 
 one of the char- 
 acters for distin- 
 guishing differ- 
 ent species of 
 FIG. ii. Various types of bacteria "colo- bacteria (Fig. IO, 
 nies " formed when growing in nutrient a and A). When 
 gelatine. Each different type of colony orowino-in cnliH 
 is produced by a different species of Sowing in SOlld 
 
 bacterium. media, such as a 
 
 nutritious liquid 
 
 made stiff with gelatine, the different species have 
 different methods of spreading from their central 
 point of origin. A single bacterium in the midst 
 of such a stiffened mass will feed upon it and pro- 
 duce descendants rapidly; but these descendants, 
 not being able to move through the gelatine, will 
 remain clustered together in a mass, which the
 
 BACTERIA AS PLANTS. 25 
 
 bacteriologist calls a colony. But their method of 
 clustering, due to different methods of growth, is 
 by no means always alike, and these colonies 
 show great differences in general appearance. 
 The differences appear to be constant, however, 
 for the same species of bacteria, and hence the 
 shape and appearance of the colony enable bac- 
 teriologists to discern different species (Fig. n). 
 All these points of difference are of practical use 
 to the bacteriologist in distinguishing species. 
 
 SPORE FORMATION. 
 
 In addition to their power of reproduction by 
 simple division, many species of bacteria have a 
 second method by means of spores. Spores are 
 special rounded or oval bits of bacteria protoplasm 
 capable of resisting adverse conditions which 
 would destroy the ordinary bacteria. They arise 
 among bacteria in two different methods. 
 
 Endogenous spores. These spores arise inside 
 of the rods or the spiral forms (Fig. 12). They 
 first appear as slight granular masses, or as dark 
 points which become gradually distinct from the 
 rest of the rod. Eventually there is thus formed 
 inside the rod a clear, highly refractive, spherical 
 or oval spore, which may even be of a greater 
 diameter than the rod producing it, thus causing 
 it to swell out and become spindle formed (Fig. 
 12 c]. These spores may form in the middle or at 
 the ends of the rods (Fig. 12). They may use up 
 all the protoplasm of the rod in their formation, 
 or they may use only a small part of it, the rod 
 which forms them continuing its activities in spite 
 of the formation of the spores within it. They are 
 always clear and highly refractive from contain-
 
 THE STORY OF GERM LIFE. 
 
 ing little water, and they do not so readily absorb 
 staining material as the ordinary rods. They ap- 
 pear to be covered with a layer of some substance 
 which resists the stain, and which also enables 
 them to resist vari- 
 ous external agen- 
 cies. This protect- 
 ive covering, to- 
 gether with their 
 small amount of 
 water, enables them 
 to resist almost any 
 amount of drying, 
 a high degree of 
 heat, and many 
 other adverse con- 
 ditions. Common- 
 ly the spores break 
 out of the rod, and 
 the rod producing 
 them dies, although 
 sometimes the rod 
 may continue its 
 activity even after 
 the spores have 
 been produced. 
 
 A r t h r ogenous 
 spores (?). Certain 
 species of bacteria 
 not produce spores as just described, but 
 
 FlG. 12. Endogenous spores: a and 
 b, Spores forming at intervals in 
 the rods ; c, Spores forming in the 
 middle of the rods and causing the 
 middle to swell ; d, Spores form- 
 ing at the end of the rods and 
 causing the end to swell. 
 
 do 
 
 may give rise to bodies that are sometimes called 
 arthrospores. These bodies are formed as short 
 segments of rods (Fig. 130). A long rod may 
 sometimes break up into several short rounded 
 elements, which are clear and appear to have a 
 somewhat increased power of resisting adverse
 
 BACTERIA AS PLANTS. 
 
 b 
 
 13. So - called arthrogenous 
 spores : a, Forming as segments 
 of rods ; b, As segments of a chain 
 of cocci. 
 
 conditions. The same may happen among the 
 spherical forms, which only in rare instances form 
 endogenous spores. 
 Among the spheres 
 which .form a chain 
 of streptococci some 
 may occasionally be 
 slightly different 
 from the rest. They 
 are a little larger, 
 and have been 
 thought to have an 
 increased resisting 
 power like that of 
 true spores (Fig. 13 FIG. 
 b}. It isquite doubt- 
 ful, however, wheth- 
 er it is proper to re- 
 gard these bodies as spores. There is no good 
 evidence that they have any special resisting 
 power to heat like endogenous spores, and bac- 
 teriologists in general are inclined to regard them 
 simply as resting cells. The term arthrospores 
 has been given to them to indicate that they are 
 formed as joints or segments, and this term may 
 be a convenient one to retain although the bodies 
 in question are not true spores. 
 
 Still a different method of spore formation 
 occurs in a few peculiar bacteria. In this case 
 ([Fig. 14) the protoplasm in the large thread breaks 
 into many minute spherical bodies, which finally 
 find exit. The spores thus formed may not be all 
 alike, differences in size being noticed. This 
 method of spore formation occurs only in a few 
 special forms of bacteria. 
 
 The matter of spore formation serves as one
 
 THE STORY OF GERM LIFE. 
 
 of the points for distinguishing species. Some 
 species do not form spores, at least under any of 
 the conditions in which they have been studied. 
 Others form them readily in almost any condition, 
 and others again only under special conditions 
 which are adverse to their 
 life. The method of spore 
 formation is always uni- 
 form for any single species. 
 Whatever be the method 
 of the formation of the 
 spore, its purpose in the 
 life of the bacterium is al- 
 ways the same. It serves 
 as a means of keeping the 
 species alive under condi- 
 tions of adversity. Its 
 power of resisting heat or 
 drying enables it to live 
 where the ordinary active 
 forms would be speedily 
 killed. Some of these 
 spores are capable of re- 
 sisting a heat of 180 C. (360 F.) for a short time, 
 and boiling water they can resist for a long time. 
 Such spores when subsequently placed under fa- 
 vourable conditions will germinate and start bac- 
 terial activity anew. 
 
 FIG. 14. Formation of 
 spores in unusual forms 
 (Crenothrix). 
 
 MOTION. 
 
 Some species of bacteria have the power of 
 active motion, and may be seen darting rapidly 
 to and fro in the liquid in which they are grow- 
 ing. This motion is produced by flagella which 
 protrude from the body. These flagella (Fig. 15)
 
 BACTERIA AS PLANTS. 
 
 29 
 
 arise from a membrane surrounding the bacterium, 
 but have an intimate connection with the proto- 
 
 FlG. 15. Bacteria provided with flagella : a, Single flagellum ; b, 
 Two flagella ; c, A tuft of flagella at one end ; d, Tufts of 
 flagella at both ends ; e, Uniform covering of flagella ; f, 
 Showing the origin of flagella from the outer layer of the body. 
 
 plasmic content. Their distribution is different 
 in different species of bacteria. Some species 
 3
 
 30 THE STORY OF GERM LIFE. 
 
 have a single flagellum at one end (Fig. 150). 
 Others have one at each end (Fig. 15 b). Others, 
 again, have, at least just before dividing, a bunch 
 at one or both ends (Fig. 15 c and d), while others, 
 again, have many flagella distributed all over the 
 body in dense profusion (Fig. 15 <?). These flagella 
 keep up a lashing to and fro in the liquid, and the 
 lashing serves to propel the bacteria through the 
 liquid. 
 
 .INTERNAL STRUCTURE. 
 
 It is hardly possible to say much about the 
 structure of the bacteria beyond the description 
 of their external forms. With all the variations 
 in detail mentioned, they are 
 extraordinarily simple, and 
 about all that can be seen is 
 their external shape. Of 
 course, they have some in- 
 ternal structure, but we 
 know very little in regard to 
 it. Some microscopists have 
 described certain appearan- 
 ces which they think indi- 
 cate internal structure. Fig. 
 16 shows some of these ap- 
 pearances. The matter is as 
 yet very obscure, however. 
 The bacteria appear to have 
 a membranous covering 
 G ' tunfrf tSria. Stn : " which sometimes is of a cel- 
 lulose nature. Within it is 
 
 protoplasm which shows various uncertain ap- 
 pearances. Some microscopists have thought 
 they could find a nucleus, and 'have regarded 
 bacteria as cells with inclosed nucleii (Figs. 10 a
 
 BACTERIA AS PLANTS. 31 
 
 and is/). Others have regarded the whole bac- 
 terium as a nucleus without any protoplasm, 
 while others, again, have concluded that the dis- 
 cerned internal structure is nothing except an ap- 
 pearance presented by the physical arrangement of 
 the protoplasm. While we may believe that they 
 have some internal structure, we must recognise 
 that as yet microscopists have not been able to 
 make it out. In short, the bacteria after two 
 centuries of study appear to us about as they did 
 at first. They must still be described as minute 
 spheres, rods, or spirals, with no further discern- 
 ible structure, sometimes motile and sometimes 
 stationary, sometimes producing spores and some- 
 times not, and multiplying universally by binary 
 fission. With all the development of the modern 
 microscope we can hardly say more than this. 
 Our advance in knowledge of bacteria is con- 
 nected almost wholly with their methods of growth 
 and the effects they produce in Nature. 
 
 ANIMALS OR PLANTS? 
 
 There has been in the past not a little ques- 
 tion as to whether bacteria should be rightly 
 classed with plants or with animals. They cer- 
 tainly have characters which ally them with both. 
 Their very common power of active independent 
 motion and their common habit of living upon 
 complex bodies for foods are animal characters, 
 and have lent force to the suggestion that they 
 are true animals. But their general form, their 
 method of growth and formation of threads, and 
 their method of spore formation are quite plant- 
 like. Their general form is very similar to a 
 group of low green plants known as Oscillaria.
 
 THE STORY OF GERM LIFE. 
 
 Fig. 17 shows a group of these Oscillarise, and 
 the similarity of this to some of the thread-like 
 
 bacteria is de- 
 cided. The Os- 
 cillari(z are, how- 
 ever, true plants, 
 and are of a 
 green colour. 
 Bacteria are 
 therefore to-day 
 looked upon as 
 a low type of 
 plant which has 
 no chlorophyll,* 
 but is related to 
 Oscillaria. The 
 absence of the 
 chlorophyll has 
 forced them to 
 adopt new rela- 
 tions to food, 
 and compels 
 them to feed 
 upon complex 
 foods instead of the simple ones, which form the 
 food of green plants. We may have no hesita- 
 tion, then, in calling them plants. It is interest- 
 ing to notice that with this idea their place in the 
 organic world is reduced to a small one systemat- 
 ically. They do not form a class by themselves, 
 but are simply a subclass, or even a family, and 
 a family closely related to several other common 
 plants. But the absence of chlorophyll and the 
 resulting peculiar life has brought about a curi- 
 
 FlG. 17. Threads of Oscillaria, the nearest 
 allies of bacteria. 
 
 * Chlorophyll is the green colouring matter of plants.
 
 BACTERIA AS PLANTS. 33 
 
 ous anomaly. Whereas their closest allies are 
 known only to botanists, and are of no interest 
 outside of their systematic relations, the bacteria 
 are familiar to every one, and are demanding the 
 life attention of hundreds of investigators. It is 
 their absence of chlorophyll and their consequent 
 dependence upon complex foods which has pro- 
 duced this anomaly. 
 
 CLASSIFICATION OF BACTERIA. 
 
 While it has generally been recognised that 
 bacteria are plants, any further classification has 
 proved a matter of great difficulty, and bacteriolo- 
 gists find it extremely difficult to devise means of 
 distinguishing species. Their extreme simplicity 
 makes it no easy matter to find points by which 
 any species can be recognised. But in spite of 
 their similarity, there is no doubt that many 
 different species exist. Bacteria which appear to 
 be almost identical, under the microscope prove 
 to have entirely different properties, and must 
 therefore be regarded as distinct species. But 
 how to distinguish them has been a puzzle. 
 Microscopists have come to look upon the differ- 
 ences in shape, multiplication, and formation of 
 spores as furnishing data sufficient to enable 
 them to divide the bacteria into genera. The 
 genus Bacillus, for instance, is the name given to 
 all rod-shaped bacteria which form endogenous 
 spores, etc. But to distinguish smaller subdi- 
 visions it has been found necessary to fall back 
 upon other characters, such as the shape of the 
 colony produced in solid gelatine, the power to 
 produce disease, or to oxidize nitrites, etc. Thus 
 at present the different species are distinguished
 
 34 THE STORY OF GERM LIFE. 
 
 rather by their physiological than their morpho- 
 logical characters. This is an unsatisfactory 
 basis of classification, and has produced much 
 confusion in the attempts to classify bacteria. 
 The problem of determining the species of bac- 
 teria is to-day a very difficult one, and with 
 our best methods is still unsatisfactorily solved. 
 A few species of marked character are well 
 known, and their powers of action so well under- 
 stood that they can be readily recognised ; but 
 of the great host of bacteria studied, the large 
 majority have been so slightly experimented upon 
 that their characters are not known, and it is im- 
 possible, therefore, to distinguish many of them 
 apart. We find that each bacteriologist working 
 in any special line commonly keeps a list of the 
 bacteria which he finds, with such data in re- 
 gard to them as he has collected. Such a list is 
 of value to him, but commonly of little value to 
 other bacteriologists from the insufficiency of the 
 data. Thus it happens that a large part of the 
 different species of bacteria described in literature 
 to-day have been found and studied by one in- 
 vestigator alone. By him they have been de- 
 scribed and perhaps named. Quite likely the 
 same species may have been found by two or 
 three other bacteriologists, but owing to the 
 difficulty of comparing results and the incom- 
 pleteness of the descriptions the identity of the 
 species is not discovered, and they are probably 
 described again under different names. The 
 same process may be repeated over and over 
 again, until the same species of bacterium will 
 come to be known by several different names, as 
 it has been studied by different observers.
 
 BACTERIA AS PLANTS. 35 
 
 VARIATION OF BACTERIA. 
 
 This matter is made even more confusing by 
 the fact that any species of bacterium may show 
 more or less variation. At one time in the his- 
 tory of bacteriology, a period lasting for many 
 years, it was the prevalent opinion that there was 
 no constancy among bacteria, but that the same 
 species might assume almost any of the various 
 forms and shapes, and possess various properties. 
 Bacteria were regarded by some as stages in the 
 life history of higher plants. This question as 
 to whether bacteria remain constant in character 
 for any considerable length of time has ever been 
 a prominent one with bacteriologists, and even 
 to-day we hardly know what the final answer will 
 be. It has been demonstrated beyond perad- 
 venture that some species may change their 
 physiological characters. Disease bacteria, for 
 instance, under certain conditions lose their 
 powers of developing disease. Species which sour 
 milk, or others which turn gelatine green, may 
 lose their characters. Now, since it is upon just 
 such physiological characters as these that we 
 must depend in order to separate different species 
 of bacteria from each other, it will be seen that 
 great confusion and uncertainty will result in our 
 attempts to define species. Further, it has been 
 proved that there is sometimes more or less of a 
 metamorphosis in the life history of certain 
 species of bacteria. The same species may form 
 a short rod, or a long thread, or break up into 
 spherical spores, and thus either a short rod, or 
 a thread, or a spherical form may belong to the 
 same species. Other species may be motile at 
 one time and stationary at another, while at a
 
 36 THE STORY OF GERM LIFE. 
 
 third period it is a simple mass of spherical 
 spores. A spherical form, when it lengthens 
 before dividing, appears as a short rod, and a 
 short rod form after dividing may be so short as 
 to appear like a spherical organism. 
 
 With all these reasons for confusion, it is not 
 to be wondered at that no satisfactory classifica- 
 tion of bacteria has been reached, or that differ- 
 ent bacteriologists do not agree as to what consti- 
 tutes a species, or whether two forms are identical 
 or not. But with all the confusion there is slowly 
 being obtained something like system. In spite 
 of the fact that species may vary and show 
 different properties under different conditions, 
 the fundamental constancy of species is every- 
 where recognised to-day as a fact. The members 
 of the same species may show different properties 
 under different conditions, but it is believed that 
 under identical conditions the properties will be 
 constant. It is no more possible to convert one 
 species into another than it is among the higher 
 orders of plants. It is believed that bacteria 
 do form a group of plants by themselves, and 
 are not to be regarded as stages in the history 
 of higher plants. It is believed that, together 
 with a considerable amount of variability and 
 an occasional somewhat long life history with 
 successive stages, there is also an essential con- 
 stancy. A systematic classification has been 
 made which is becoming more or less satisfactory. 
 We are constantly learning more and more of the 
 characters, so that they can be recognised in 
 different places by different observers. It is the 
 conviction of all who work with bacteria that, in 
 spite of the difficulties, it is only a matter of time 
 when we shall have a classification and descrip-
 
 BACTERIA AS PLANTS. 37 
 
 tion of bacteria so complete as to characterize 
 the different species accurately. 
 
 Even with our present incomplete knowledge 
 of what characterizes a species, it is necessary to 
 use some names. Bacteria are commonly given a 
 generic name based upon their microscopic ap- 
 pearance. There are only a few of these names. 
 Micrococcus, Streptococcus, Staphylococcus, Sarcina, 
 Bacterium, Bacillus, Spirillum, are all the names in 
 common use applying to the ordinary bacteria. 
 There are a few others less commonly used. To 
 this generic name a specific name is commonly 
 added, based upon some physiological character. 
 For example, Bacillus typhosus is the name given 
 to the bacillus which causes typhoid fever. Such 
 names are of great use when the species is a com- 
 mon and well-known one, but of doubtful value 
 for less-known species. It frequently happens 
 that a bacteriologist makes a study of the bac- 
 teria found in a certain locality, and obtains thus 
 a long list of species hitherto unknown. In these 
 cases it is common simply to number these spe- 
 cies rather than name them. This method is fre- 
 quently advisable, since the bacteriologist can 
 seldom hunt up all bacteriological literature with 
 sufficient accuracy to determine whether some 
 other bacteriologist may not have found the 
 same species in an entirely different locality. 
 One bacteriologist, for example, finds some sev- 
 enty different species of bacteria in different 
 cheeses. He studies them enough for his own 
 purposes, but not sufficiently to determine whether 
 some other person may not have found the same 
 species perhaps in milk or water. He therefore sim- 
 ply numbers them a method which conveys no 
 suggestion as to whether they may be new species
 
 38 THE STORY OF GERM LIFE. 
 
 or not. This method avoids the giving of separate 
 names to the same species found by different 
 observers, and it is hoped that gradually accumu- 
 lating knowledge will in time group together the 
 forms which are really identical, but which have 
 been described by different observers. 
 
 WHERE BACTERIA ARE FOUND. 
 
 There are no other plants or animals so uni- 
 versally found in Nature as the bacteria. It is 
 this universal presence, together with their great 
 powers of multiplication, which renders them of 
 so much importance in Nature. They exist almost 
 everywhere on the surface of the earth. They 
 are in the soil, especially at its surface. They do 
 not extend to very great depths of soil, however, 
 few existing below four feet of soil. At the sur- 
 face they are very abundant, especially if the soil 
 is moist and full of organic material. The num- 
 ber may range from a few hundred to one hun- 
 dred millions per gramme.* The soil bacteria 
 vary also in species, some twoscore different spe- 
 cies having been described as common in soil. 
 They are in all bodies of water, both at the 
 surface and below it. They are found at con- 
 siderable depths in the ocean. All bodies of fresh 
 water contain them, and all sediments in such 
 bodies of water are filled with bacteria. They 
 are in streams of running water in even greater 
 quantity than in standing water. This is simply 
 because running streams are being constantly 
 supplied with water which has been washing the 
 surface of the country and thus carrying off all 
 
 * One gramme is fifteen grains.
 
 BACTERIA AS PLANTS. 39 
 
 surface accumulations. Lakes or reservoirs, how- 
 ever, by standing quiet allow the bacteria to set- 
 tle to the bottom, and the water thus gets some- 
 what purified. They are in the air, especially in 
 regions of habitation. Their numbers are great- 
 est near the surface of the ground, and decrease 
 in the upper strata of air. Anything which 
 tends to raise dust increases the number of bac- 
 teria in the air greatly, and the dust and emana- 
 tions from the clothes of people crowded in a 
 close room fill the air with bacteria in very great 
 numbers. They are found in excessive abun- 
 dance in every bit of decaying matter wherever it 
 may be. Manure heaps, dead bodies of animals, 
 decaying trees, filth and slime and muck every- 
 where are filled with them, for it is in such places 
 that they find their best nourishment. The bod- 
 ies of animals contain them in the mouth, stom- 
 ach, and intestine in great numbers, and this is, of 
 course, equally true of man. On the surface of 
 the body they cling in great quantity ; attached 
 to the clothes, under the finger nails, among the 
 hairs, in every possible crevice or hiding place in 
 the skin, and in all secretions. They do not, 
 however, occur in the tissues of a healthy indi- 
 vidual, either in the blood, muscle, gland, or any 
 other organ. Secretions, such as milk, urine, etc., 
 always contain them, however, since the bacteria 
 do exist in the ducts of the glands which conduct 
 the secretions to the exterior, and thus, while the 
 bacteria are never in the healthy gland itself, 
 they always succeed in contaminating the secre- 
 tion as it passes to the exterior. Not only higher 
 animals, but the lower animals also have their bod- 
 ies more or less covered with bacteria. Flies have 
 them on their feet, bees among their hairs, etc.
 
 40 THE STORY OF GERM LIFE. 
 
 In short, wherever on the face of Nature there 
 is a lodging place for dust there will be found 
 bacteria. In most of these localities they are 
 dormant, or at least growing only a little. The 
 bacteria clinging to the dry hair can grow but lit- 
 tle, if at all, and those in pure water multiply very 
 little. When dried as dust they are entirely dor- 
 mant. But each individual bacterium or spore 
 has the potential power of multiplication already 
 noticed, and as soon as it by accident falls upon 
 a place where there is food and moisture it will 
 begin to multiply. Everywhere in Nature, then, 
 exists this group of organisms with its almost in- 
 conceivable power of multiplication, but a power 
 held in check by lack of food. Furnish them 
 with food and their potential powers become 
 actual. Such food is provided by the dead bod- 
 ies of animals or plants, or by animal secretions, 
 or from various other sources. The bacteria which 
 are fortunate enough to get furnished with such 
 food material continue to feed upon it until the 
 food supply is exhausted or their growth is 
 checked in some other way. They may be re- 
 garded, therefore, as a constant and universal 
 power usually held in check. With their uni- 
 versal presence and their powers of producing 
 chemical changes in food material, they are ever 
 ready to produce changes in the face of Nature, 
 and to these changes we will now turn.
 
 USE OF BACTERIA IN THE ARTS. 41 
 
 CHAPTER II. 
 
 MISCELLANEOUS USE OF BACTERIA IN THE ARTS. 
 
 THE foods upon which bacteria live are in 
 endless variety, almost every product of animal 
 or vegetable life serving to supply their needs. 
 Some species appear to require somewhat definite 
 kinds of food, and have therefore rather narrow 
 conditions of life, but the majority may live upon 
 a great variety of organic compounds. As they 
 consume the material which serves them as food 
 they produce chemical changes therein. These 
 changes are largely of a nature that the chemist 
 knows as decomposition changes. By this is 
 meant that the bacteria, seizing hold of ingre- 
 dients which constitute their food, break them to 
 pieces chemically. The molecule of the original 
 food matter is split into simpler molecules, and 
 the food is thus changed in its chemical nature. 
 As a result, the compounds which appear in the 
 decomposing solution are commonly simpler than 
 the original food molecules. Such products are 
 in general called decomposition products, or some- 
 times cleavage products. Sometimes, however, the 
 bacteria have, in addition to their power of pull- 
 ing their food to pieces, a further power of build- 
 ing other compounds out of the fragments, thus 
 building up as well as pulling down. But, how- 
 ever they do it, bacteria when growing in any 
 food material have the power of giving rise to 
 numerous products which did not exist in the 
 food mass before. Because of their extraordi- 
 nary powers of reproduction they are capable of 
 producing these changes very rapidly and can
 
 42 THE STORY OF GERM LIFE. 
 
 give rise in a short time to large amounts of the 
 peculiar products of their growth. 
 
 It is to these powers of producing chemical 
 changes in their food that bacteria owe all their 
 importance in the world. Their power of chem- 
 ically destroying the food products is in itself of 
 no little importance, but the products which arise 
 as the result of this series of chemical changes 
 are of an importance in the world which we are 
 only just beginning to appreciate. In our at- 
 tempt to outline the agency which bacteria play 
 in our industries and in natural processes as well, 
 we shall notice that they are sometimes of value 
 simply for their power of producing decomposi- 
 tion ; but their greatest value lies in the fact that 
 they are important agents because of the prod- 
 ucts of their life. 
 
 We may notice, in the first place, that in the 
 arts there are several industries which may prop- 
 erly be classed together as maceration industries, 
 all of which are based upon the decomposition 
 powers of bacteria. Hardly any animal or vege- 
 table substance is able to resist their softening 
 influence, and the artisan relies upon this power 
 in several different directions. 
 
 BENEFITS DERIVED FROM POWERS OF 
 DECOMPOSITION. 
 
 Linen. Linen consists of certain woody fibres 
 of the stem of the flax. The flax stem is not 
 made up entirely of the valuable fibres, but 
 largely of more brittle wood fibres, which are of 
 no use. The valuable fibres are, however, close- 
 ly united with the wood and with each other in 
 such an intimate fashion that it is impossible to
 
 USE OF BACTERIA IN THE ARTS. 43 
 
 separate them by any mechanical means. The 
 whole cellular substance of the stem is bound 
 together by some cementing materials which hold 
 it in a compact mass, probably a salt of calcium 
 and pectinic acid. The art of preparing flax is 
 a process of getting rid of the worthless wood 
 fibres and preserving the valuable, longer, tougher, 
 and more valuable fibres, which are then made 
 into linen. But to separate them it is necessary 
 first to soften the whole tissue. This is always 
 done through the aid of bacteria. The flax stems, 
 after proper preparation, are exposed to the ac- 
 tion of moisture and heat, which soon develops a 
 rapid bacterial growth. Sometimes this is done 
 by simply exposing the flax to the dew and rain 
 and allowing it to lie thus exposed for some time. 
 By another process the stems are completely im- 
 mersed in water and allowed to remain for ten to 
 fourteen days. By a third process the water in 
 which the flax is immersed is heated from 75 to 
 90 F., with the addition of certain chemicals, for 
 some fifty to sixty hours. In all cases the effect 
 is the same. The moisture and the heat cause a 
 growth of bacteria which proceeds with more or 
 less rapidity according to the temperature and 
 other conditions. A putrefactive fermentation is 
 thus set up which softens the gummy substance 
 holding the fibres together. The process is known 
 as "retting," and after it is completed the fibres 
 are easily isolated from each other. A purely 
 mechanical process now easily separates the valu- 
 able fibres from the wood fibres. The whole pro- 
 cess is a typical fermentation. A disagreeable 
 odour arises from the fermenting flax, and the 
 liquid after the fermentation is filled with prod- 
 ucts which make valuable manure. The process
 
 44 THE STORY OF GERM LIFE. 
 
 has not been scientifically studied until very re- 
 cently. The bacillus which produces the " ret- 
 ting " is known now, however, and it has been 
 shown that the " retting " is a process of decom- 
 position of the pectin cement. No method of 
 separating the linen fibres in the flax from the 
 wood fibres has yet been devised which dispenses 
 with the aid of bacteria. 
 
 Jute and Hemp. Almost exactly the same use 
 is made of bacterial action in the manufacture of 
 jute and hemp. The commercial aspect of the 
 jute industry has grown to be a large one, involv- 
 ing many millions of dollars. Like linen, jute is 
 a fibre of the inner bark of a plant, and is mixed 
 in the bark with a mass of other useless fibrous 
 material. As in the case of linen, a fermenta- 
 tion by bacteria is depended upon as a means of 
 softening the material so that the fibres can be 
 disassociated. The process is called " retting," 
 as in the linen manufacture. The details of the 
 process are somewhat different. The jute is com- 
 monly fermented in tanks of stagnant water, al- 
 though sometimes it is allowed to soak in river 
 water for a sufficient length of time to produce 
 the softening. After the fermentation is thus 
 started the jute fibre is separated from the wood, 
 and is of a sufficient flexibility and toughness to 
 be woven into sacking, carpets, curtains, table 
 covers, and other coarse cloth. 
 
 Practically the same method is used in sepa- 
 rating the tough fibres of the hemp. The hemp 
 plant contains some long flexible fibres with others 
 of no value, and bacterial fermentation is relied 
 upon to soften the tissues so that they may be 
 separated. 
 
 Cocoanut fibre, a somewhat similar material, is
 
 USE OF BACTERIA IN THE ARTS. 45 
 
 obtained from the husk of the cocoanut by the 
 same means. The unripened husk is allowed to 
 steep and ferment in water for a long time, six 
 months or a year being required. By this time 
 the husk has become so softened that it can be 
 beaten until the fibres separate and can be re- 
 moved. They are subsequently made into a num- 
 ber of coarse articles, especially valuable for their 
 toughness. Door mats, brushes, ships' fenders, 
 etc., are illustrations of the sort of articles made 
 from them. 
 
 In each of these processes the fermentation 
 must have a tendency to soften the desired fibres 
 as well as the connecting substance. Putrefac- 
 tion attacks all kinds of vegetable tissue, and if 
 this "retting" continues too long the desired 
 fibre is decidedly injured by the softening effect 
 of the fermentation. It is quite probable that, 
 even as commonly carried on, the fermentation 
 has some slight injurious effect upon the fibre, 
 and that if some purely mechanical means could 
 be devised for separating the fibre from the wood 
 it would produce a better material. But such 
 mechanical means has not been devised, and at 
 present a putrefactive fermentation appears to 
 be the only practical method of separating the 
 fibres. 
 
 Sponges. A somewhat similar use is made 
 of bacteria in the commercial preparation of 
 sponges. The sponge of commerce is simply 
 the fibrous skeleton of a marine animal. When 
 it is alive this skeleton is completely filled with 
 the softer parts of the animal, and to fit the 
 sponge for use this softer organic material must 
 be got rid of. It is easily accomplished by rot- 
 ting. The fresh sponges are allowed to stand in 
 4
 
 ^6 THE STORY OF GERM LIFE. 
 
 the warm sun and very rapidly decay. Bacteria 
 make their way into the sponge and thoroughly 
 decompose the soft tissues. After a short putre- 
 faction of this sort the softened organic matter 
 can be easily washed out of the skeleton and 
 leave the clean fibre ready for market. 
 
 Leather preparation. The tanning of leather 
 is a purely chemical process, and in some pro- 
 cesses the whole operation of preparing the 
 leather is a chemical one. In others, however, 
 especially in America, bacteria are brought into 
 action at one stage. The dried hide which comes 
 to the tannery must first have the hair removed 
 together with the outer skin. The hide for this 
 purpose must be moistened and softened. In 
 some tanneries this is done by steeping it in 
 chemicals. In others, however, it is put into 
 water and slightly heated until fermentation 
 arises. The fermentation softens it so that the 
 outer skin can be easily removed with a knife, 
 and the removal of hair is accomplished at the 
 same time. Bacterial putrefaction in the tannery 
 is thus an assistance in preparing the skin for 
 the tanning proper. Even in the subsequent 
 tanning a bacterial fermentation appears to 
 play a part, but little is yet known in regard 
 to it. 
 
 Maceration of skeletons. The making of skele- 
 tons for museums and anatomical instruction in 
 general is no very great industry, and yet it is 
 one of importance. In the making of skeletons 
 the process of maceration is commonly used as 
 an aid. The maceration consists simply in allow- 
 ing the skeleton to soak in water for a day or 
 two after cleaning away the bulk of the muscles. 
 The putrefaction that arises softens the connect-
 
 USE OF BACTERIA IN THE ARTS. 47 
 
 ive tissues so much that the bones may be readily 
 cleaned of flesh. 
 
 Citric acid. Bacterial fermentation is em- 
 ployed also in the ordinary preparation of citric 
 acid. The acid is made chiefly from the juice of 
 the lemon. The juice is pressed from the fruit 
 and then allowed to ferment. The fermentation 
 aids in separating a mucilaginous mass and mak- 
 ing it thus possible to obtain the citric acid in a 
 purer condition. The action is probably similar 
 to the maceration processes described above, al- 
 though it has not as yet been studied by bacteri- 
 ologists. 
 
 BENEFITS DERIVED FROM THE PRODUCTS OF 
 BACTERIAL LIFE. 
 
 While bacteria thus play a part in our indus- 
 tries simply from their power of producing de- 
 composition, it is primarily because of the prod- 
 ucts of their action that they are of value. 
 Wherever bacteria seize hold of organic matter 
 and feed upon it, there are certain to be devel- 
 oped new chemical compounds, resulting largely 
 from decomposition, but partly also from con- 
 structive processes. These new compounds are 
 of great variety. Different species of bacteria 
 do not by any means produce the same com- 
 pounds even when growing in and decomposing 
 the same food material. Moreover, the same 
 species of bacteria may give rise to different 
 products when growing in different food mate- 
 rials. Some of the compounds produced by such 
 processes are poisonous, others are harmless. 
 Some are gaseous, others are liquids. Some 
 have peculiar odours, as may be recognised from
 
 48 THE STORY OF GERM LIFE. 
 
 the smell arising from a bit of decaying meat. 
 Others have peculiar tastes, as may be realized 
 in the gamy taste of meat which is in the incipi- 
 ent stages of putrefaction. By purely empirical 
 means mankind has learned methods of encourag- 
 ing the development of some of these products, and 
 is to-day making practical use of this power, pos- 
 sessed by bacteria, of furnishing desired chemical 
 compounds. Industries involving the investment 
 of hundreds of millions of dollars are founded 
 upon the products of bacterial life, and they have 
 a far more important relation to our everyday 
 life than is commonly imagined. In many cases 
 the artisan who is dependent upon this action of 
 microscopic life is unaware of the fact. His 
 processes are those which experience has taught 
 produce desired results, but, nevertheless, his 
 dependence upon bacteria is none the less funda- 
 mental. 
 
 BACTERIA IN THE FERMENTATIVE INDUSTRIES. 
 
 We may notice, first, several miscellaneous in- 
 stances of the application of bacteria to various 
 fermentative industries where their aid is of more 
 or less value to man. In some of the examples 
 to be mentioned the influence of bacteria is pro- 
 found and fundamental, while in others it is only 
 incidental. The fermentative industries of civili- 
 zation are gigantic in extent, and have come to 
 be an important factor in modern civilized life. 
 The large part of the fermentation is based upon 
 the growth of a class of microscopic plants which 
 we call yeasts. Bacteria and yeasts are both 
 microscopic plants, and perhaps somewhat close- 
 ly related to each other. The botanist finds a
 
 USE OF BACTERIA IN THE ARTS. 49 
 
 difference between them, based upon their method 
 of multiplication, and therefore places them in 
 different classes (Fig. 2, page 19). In their gen- 
 eral power of producing chemical changes in their 
 food products, yeasts agree closely with bacteria, 
 though the kinds of chemical changes are differ- 
 ent. The whole of the great fermentative indus- 
 tries, in which are invested hundreds of millions 
 of dollars, is based upon chemical decompositions 
 produced by microscopic plants. In the great 
 part of commercial fermentations alcohol is the 
 product desired, and alcohol, though it is some- 
 times produced by bacteria, is in commercial 
 quantities produced only by yeasts. Hence it is 
 that, although the fermentations produced by 
 bacteria are more common in Nature than those 
 produced by yeasts and give rise to a much larger 
 number of decomposition products, still their com- 
 mercial aspect is decidedly less important than 
 that of yeasts. Nevertheless, bacteria are not 
 without their importance in the ordinary ferment- 
 ative processes. Although they are of no im- 
 portance as aids in the common fermentative 
 processes, they are not infrequently the cause of 
 much trouble. In the fermentation of malt to 
 produce beer, or grape juice to produce wine, it 
 is the desire of the brewer and vintner to have 
 this fermentation produced by pure yeasts, un- 
 mixed with bacteria. If the yeast is pure the 
 fermentation is uniform and successful. But the 
 brewer and vintner have long known that the 
 fermentation is frequently interfered with by ir- 
 regularities. The troubles which arise have long 
 been known, but the bacteriologist has finally 
 discovered their cause, and in general their rem- 
 edy. The cause of the chief troubles which arise
 
 50 THE STORY OF GERM LIFE. 
 
 in the fermentation is the presence of contami- 
 nating bacteria among the yeasts. These bac- 
 teria have been more or less carefully studied by 
 bacteriologists, and their effect upon the beer or 
 wine determined. Some of them produce acid 
 and render the products sour; others make them 
 bitter ; others, again, produce a slimy material 
 which makes the wine or beer "ropy." Some- 
 thing like a score of bacteria species have been 
 found liable to occur in the fermenting mate- 
 rial and destroy the value of the product of both 
 the wine maker and the beer brewer. The spe- 
 cies of bacteria which infect and injure wine are 
 different from those which infect and injure beer. 
 They are ever present as possibilities in the great 
 alcoholic fermentations. They are dangers which 
 must be guarded against. In former years the 
 troubles from these sources were much greater 
 than they are at present. Since it has been dem- 
 onstrated that the different imperfections in the 
 fermentative process are due to bacterial impuri- 
 ties, commonly in the yeasts which are used to 
 produce the fermentation, methods of avoiding 
 them are readily devised. To-day the vintner 
 has ready command of processes for avoiding 
 the troubles which arise from bacteria, and the 
 brewer is always provided with a microscope to 
 show him the presence or absence of the con- 
 taminating bacteria. While, then, the alcoholic 
 fermentations are not dependent upon bacteria, 
 the proper management of these fermentations 
 requires a knowledge of their habits and char- 
 acters. 
 
 There are certain other fermentative processes 
 of more or less importance in their commercial as- 
 pects, which are directly dependent upon bacte-
 
 USE OF BACTERIA IN THE ARTS. 5 1 
 
 riai action Some of them we should unhesitat- 
 ingly look upon as fermentations, while others 
 would hardly be thought of as belonging to the 
 fermentation industries. 
 
 The commercial importance of the manufac- 
 ture of vinegar, though large, does not, of course, 
 compare in extent with that of the alcoholic fer- 
 mentations. Vinegar is a weak solution of acetic 
 acid, together with various other ingredients 
 which have come from the materials furnishing 
 the acid. In the manufacture of vinegar, alcohol 
 is always used as the source of the acetic acid. 
 The production of acetic acid from alcohol is a 
 simple oxidation. The equation C 2 H 6 O -|- O 2 = 
 C 2 H 4 O 2 +H 8 O shows the chemical change that 
 occurs. This oxidation can be brought about by 
 purely chemical means. While alcohol will not 
 readily unite with oxygen under common condi- 
 tions, if the alcohol is allowed to pass over a bit 
 of platinum sponge the union readily occurs and 
 acetic acid results. This method of acetic-acid 
 production is possible experimentally, but is im- 
 practicable on any large scale. In the ordinary 
 manufacture of vinegar the oxidation is a true 
 fermentation, and brought about by the growth of 
 bacteria. 
 
 In the commercial manufacture of vinegar 
 several different weak alcoholic solutions are 
 used. The most common of these are fermented 
 malt, weak wine, cider, and sometimes a weak so- 
 lution of spirit to which is added sugar and malt. 
 If these solutions are allowed to stand for a time 
 in contact with air, they slowly turn sour by the
 
 52 THE STORY OF GERM LIFE. 
 
 gradual conversion of the alcohol into acetic acid. 
 At the close of the process practically all of the 
 alcohol has disappeared. Ordinarily, however, 
 not all of it has been converted into acetic acid, 
 for the oxidation does not all sf^p at this step. 
 As tffe oxidation goes on, some of the acid is 
 oxidized into carbonic dioxide, which is, of course, 
 dissipated at once into the airj and if the process 
 is allowed to continue unchecked for a long 
 enough period much of the acetic acid will be lost 
 in this way. 
 
 The oxidation of the alcohol in all commer- 
 cial production of vinegar is brought about by 
 the growth of bacteria fflvthe liquid. When the 
 vinegar production is going on properly, there is 
 formed on the top of the liquid a dense felted mass 
 known as the "mother of vinegar." This mass 
 proves to be made of bacteria which have the 
 power of absorbing oxygen from the air, or, at all 
 events, of causing the alcohol to unite with oxy- 
 gen. It was at first thought that a single species 
 of bacterium was thus the cause of the oxidation 
 of alcohol, and this was named Mycoderma aceti. 
 But further study has shown that several have 
 the power, and that even in the commercial man- 
 ufacture of vinegar several species play a part 
 (Fig. 18), although the different species are not yet 
 very thoroughly studied. Each appears to act 
 best under different conditions. Some of them 
 act slowly, and others rapidly, the slow-growing 
 species appearing to produce the larger amount 
 of acid in the end. After the amount of acetic 
 acid reaches a certain percentage, the bacteria are 
 unable to produce more, even though there be al- 
 cohol still left unoxidized. A percentage as high 
 as fourteen per cent, commonly destroys all their
 
 USE OF BACTERIA IN THE ARTS. 
 
 53 
 
 power of growth. The production of the acid is 
 wholly dependent upon the growth of the bacteria, 
 and the secret of the successful vinegar manu- 
 facture is the skilful manipulation of these bac- 
 
 FlG. 18. Bacillus aceticum, the bacterium which is the common 
 cause of the vinegar fermentation. 
 
 teria so as to keep them in the purest condition 
 and to give them the best opportunity for growth. 
 One method of vinegar manufacture which is 
 quite rapid is carried on in a slightly different 
 manner. A tall cylindrical chamber is filled with 
 wood shavings, and a weak solution of alcohol is 
 allowed to trickle slowly through it. The liquid 
 after passing over the shavings comes out after a 
 number of hours well charged with acetic acid. 
 This process at first sight appears to be a purely 
 chemical one, and reminds us of the oxidation 
 which occurs when alcohol is allowed to pass 
 over a platinum sponge. It has been claimed, 
 indeed, that this is a chemical oxidation in which 
 bacteria play no part. But this appears to be an
 
 54 THE STORY OF GERM LIFE. 
 
 error. It is always found necessary in this method 
 to start the process by pouring upon the shavings 
 some warm vinegar. Unless in this way the shav- 
 ings become charged with the vinegar-holding 
 bacteria the alcohol will not undergo oxidation 
 during its passage over them, and after the bac- 
 teria thus introduced have grown enough to coat 
 the shavings thoroughly the acetic-acid produc- 
 tion is much more rapid than at first. If vinegar 
 is allowed to trickle slowly down a suspended 
 string, so that its bacteria may distribute them- 
 selves through the string, and then alcohol be al- 
 lowed to trickle over it in the same way, the oxida- 
 tion takes place and acetic acid is formed. From 
 the accumulation of such facts it has come to be 
 recognised that all processes for the commercial 
 manufacture of vinegar depend upon the action 
 of bacteria. While the oxidation of alcohol into 
 acetic acid may take place by purely chemical 
 means, these processes are not practical on a large 
 scale, and vinegar manufacturers everywhere de- 
 pend upon bacteria as their agents in producing 
 the oxidation. These bacteria, several species in 
 all, feed upon the nitrogenous matter in the fer- 
 menting mass and produce the desired change in 
 the alcohol. 
 
 This vinegar fermentation is subject to cer- 
 tain irregularities, and the vinegar manufacturers 
 can not always depend upon its occurring in a 
 satisfactory manner. Just as in brewing, so here, 
 contaminating bacteria sometimes find their way 
 into the fermenting mass and interfere with its 
 normal course. In particular, the flavour of the 
 vinegar is liable to suffer from such causes. As 
 yet our vinegar manufacturers have not applied 
 to acetic fermentation the same principle which
 
 USE OF BACTERIA IN THE ARTS. 55 
 
 has been so successful in brewing namely, the 
 use, as a starter of the fermentation, of a pure cul- 
 ture of the proper species of bacteria. This has 
 been done experimentally and proves to be feas- 
 ible. In practice, however, vinegar makers find 
 that simpler methods of obtaining a starter by 
 means of which they procure a culture nearly 
 though not absolutely pure are perfectly satis- 
 factory. It is uncertain whether really pure cul- 
 tures will ever be used in this industry. 
 
 LACTIC ACID. 
 
 The manufacture of lactic acid is an industry 
 of less extent than that of acetic acid, and yet it 
 is one which has some considerable commercial 
 importance. Lactic acid is used in no large quan- 
 tity, although it is of some value as a medicine 
 and in the arts. For its production we are wholly 
 dependent upon bacteria. It is this acid which, 
 as we shall see, is produced in the ordinary 
 souring of milk, and a large number of species 
 of bacteria are capable of producing the acid 
 from milk sugar. Any sample of sour milk may 
 therefore always be depended upon to contain 
 plenty of lactic organisms. In its manufacture 
 for commercial purposes milk is sometimes used 
 as a source, but more commonly other substances. 
 Sometimes a mixture of cane sugar and tartaric 
 acid is used. To start the fermentation the mix- 
 ture is inoculated with a mass of sour milk or de- 
 caying cheese, or both, such a mixture always con- 
 taining lactic organisms. To be sure, it also 
 contains many other bacteria which have differ- 
 ent effects, but the acid producers are always so 
 abundant and grow so vigorously that the lactic
 
 56 THE STORY OF GERM LIFE. 
 
 fermentation occurs in spite of all other bacteria. 
 Here also there is a possibility of an improve- 
 ment in the process by the use of pure cultures of 
 lactic organisms. Up to the present, however, 
 there has been no application of such methods. 
 The commercial aspects of the industry are not 
 upon a sufficiently large scale to call for much in 
 this direction. 
 
 At the present time the only method we have 
 for the manufacture of lactic acid is dependent 
 upon bacteria. Chemical processes for its manu- 
 facture are known, but not employed commer- 
 cially. There are several different kinds of lac- 
 tic acid. They differ from each other in the 
 relations of the atoms within their molecule, and 
 in their relation to polarized light, some forms 
 rotating the plane of polarized light to the right, 
 others to the left, while others are inactive in this 
 respect. All the types are produced by fermenta- 
 tion processes, different species of bacteria hav- 
 ing powers of producing the different types. 
 
 BUTYRIC ACID. 
 
 Butyric acid is another acid for which we are 
 chiefly dependent upon bacteria. This acid is of 
 no very great importance, arid its manufacture 
 can hardly be called an industry ; still it is to a 
 certain extent made, and is an article of commerce. 
 It is an acid that can be manufactured by chemical 
 means, but, as in the case of the last two acids, its 
 commercial manufacture is based upon bacterial 
 action. Quite a number of species of bacteria 
 can produce butyric acid, and they produce it from 
 a variety of different sources. Butyric acid is a 
 common ingredient in old milk and in butter, and
 
 THE USE OF BACTERIA IN THE ARTS. 57 
 
 its formation by bacteria was historically one of 
 the first bacterial fermentations to be clearly un- 
 derstood It can be produced also in various 
 sugar and starchy solutions. Glycerine may also 
 undergo a butyric fermentation. The presence 
 of this acid is occasionally troublesome, since it 
 is one of the factors in the rancidity of butter and 
 other similar materials. 
 
 INDIGO PREPARATION. 
 
 The preparation of indigo from the indigo plant 
 is a fermentative process brought about by a spe- 
 cific bacterium. The leaves of the plant are im- 
 mersed in water in a large vat, and a rapid fer- 
 mentation arises. As a result of the fermentation 
 the part of the plant which is the basis of the in- 
 digo is separated from the leaves and dissolved in 
 the water ; and as a second feature of the fer- 
 mentation the soluble material is changed in its 
 chemical nature into indigo proper. As this 
 change occurs the characteristic blue colour is de- 
 veloped, and the material is rendered insoluble in 
 water. It therefore makes its appearance as a 
 blue mass separated from the water, and is then 
 removed as indigo. 
 
 Of the nature of the process we as yet know 
 very little. That it is a fermentation is certain, 
 and it has been proved that it is produced by a 
 definite species of bacterium which occurs on the 
 indigo leaves. If the sterilized leaves are placed 
 in sterile water no fermentation occurs and no 
 indigo is formed. If, however, some of the spe- 
 cific bacteria are added to the mass the fermenta- 
 tion soon begins and the blue colour of the indigo 
 makes its appearance. It is plain, therefore, that
 
 58 THE STORY OF GERM LIFE. 
 
 indigo is a product of bacterial fermentation, and 
 commonly due to a single definite species of bac- 
 terium. Of the details of the formation, however, 
 we as yet know little, and no practical applica- 
 tion of the facts have yet been made. 
 
 BACTERIA IN TOBACCO CURING. 
 
 A fermentative process of quite a different na- 
 ture, but of immense commercial value, is found 
 in the preparation of tobacco. The process by 
 which tobacco is prepared is a long and some- 
 what complicated one, consisting of a number of 
 different stages. The tobacco, after being first 
 dried in a careful manner, is subsequently allowed 
 to absorb moisture from the atmosphere, and is 
 then placed in large heaps to undergo a further 
 change. This process appears to be a fermenta- 
 tion, for the temperature of the mass rises rapidly, 
 and every indication of a fermentative action is 
 seen. The tobacco in these heaps is changed 
 occasionally, the heap being thrown down and 
 built up again in such a way that the portion 
 which was first at the bottom comes to the top, 
 and in this way all parts of the heap may be- 
 come equally affected by the process. After this 
 process the tobacco is sent to the different manu- 
 facturers, who finish the process of curing. The 
 further treatment it receives varies widely ac- 
 cording to the desired product, whether for smok- 
 ing or for snuff, etc. In all cases, however, 
 fermentations play a prominent part. Some- 
 times the leaves are directly inoculated with fer- 
 menting material. In the preparation of snuff 
 the details of the process are more complicated 
 than in the preparation of smoking tobacco. The
 
 THE USE OF BACTERIA IN THE ARTS. 59 
 
 tobacco, after being ground and mixed with cer- 
 tain ingredients, is allowed to undergo a fermen- 
 tation which lasts for weeks, and indeed for 
 months. In the different methods of preparing 
 snuff the fermentations take place in different 
 ways, and sometimes the tobacco is subjected to 
 two or three different fermentative actions. The 
 result of the whole is the slow preparation of the 
 commercial product. It is during the final fer- 
 mentative processes that the peculiar colour and 
 flavour of the snuff are developed, and it is during 
 the fermentation of the leaves of the smoking to- 
 bacco either the original fermentation or the 
 subsequent ones that the special flavours and 
 aromas of tobacco are produced. 
 
 It can not be claimed for a moment that these 
 changes by which the tobacco is cured and finally 
 brought to a marketable condition are due wholly 
 to bacteria. There is no question that chemical 
 and physical phenomena play an important part 
 in them. Nevertheless, from the moment when 
 the tobacco is cut in the fields until the time it is 
 ready for market the curing is very intimately 
 associated with bacteria and fermentative organ- 
 isms in general. Some of these processes are 
 wholly brought about by bacterial life ; in others 
 the micro-organisms aid the process, though they 
 perhaps can not be regarded as the sole agents. 
 
 At the outset the tobacco producer has to 
 contend with a number of micro-organisms which 
 may produce diseases in his tobacco. During the 
 drying process, if the temperature or the amount 
 of moisture or the access of air is not kept in a 
 proper condition, various troubles arise and va- 
 rious diseases make their appearance, which either 
 injure or ruin the value of the product. These
 
 60 THE STORY OF GERM LIFE. 
 
 appear to be produced by micro-organisms of 
 different sorts. During the fermentation which 
 follows the drying the producer has to contend 
 with micro-organisms that are troublesome to him ; 
 for unless the phenomena are properly regulated 
 the fermentation that occurs produces effects 
 upon the tobacco which ruin its character. From 
 the time the tobacco is cut until the final stage 
 in the curing the persons engaged in preparing 
 it for market must be on a constant watch to 
 prevent the growth within it of undesirable or- 
 ganisms. The preparation of tobacco is for this 
 reason a delicate operation, and one that will be 
 very likely to fail unless the greatest care is taken. 
 In the several fermentative processes which 
 occur in the preparation there is no question that 
 micro-organisms aid the tobacco producer and 
 manufacturer. Bacteria produce the first fermen- 
 tation that follows the drying, and it is these or- 
 ganisms too, in large measure, that give rise to 
 all the subsequent fermentations, although seem- 
 ingly in some cases purely chemical processes 
 materially aid. Now the special quality of the 
 tobacco is in part dependent upon the peculiar 
 type of fermentation which occurs in one or an- 
 other of these fermenting actions. It is the fer- 
 mentation that gives rise to the peculiar flavour 
 and to the aroma of the different grades of tobacco. 
 Inasmuch as the various flavours which charac- 
 terize tobacco of different grades are developed, 
 at least to a large extent, during the fermentation 
 processes, it is a natural supposition that the dif- 
 ferent qualities of the tobacco, so far as concerns 
 flavour, are due to the different types of fermen- 
 tation. The number of species of bacteria which 
 are found upon the tobacco leaves in the various
 
 THE USE OF BACTERIA IN THE ARTS. 6 1 
 
 stages of its preparation is quite large, and from 
 what we have already learned it is inevitable that 
 the different kinds of bacteria will produce dif- 
 ferent results in the fermenting process. It 
 would seem natural, therefore, to assume that the 
 different flavours of different grades may not un- 
 likely be due to the fact that the tobacco in the 
 different cases has been fermented under the in- 
 fluence of different kinds of bacteria. 
 
 Nor is this simply a matter of inference. To a 
 certain extent experimental evidence has borne out 
 the conclusion, and has given at least a slight in- 
 dication of practical results in the future. Acting 
 upon the suggestion that the difference between 
 the high grades of tobacco and the poorer grades 
 is due to the character of the bacteria that pro- 
 duce the fermentation, certain bacteriologists 
 have attempted to obtain from a high quality of 
 tobacco the species of bacteria which are infesting 
 it. These bacteria have then been cultivated by 
 bacteriological methods and used in experiments 
 for the fermentation of tobacco. If it is true that 
 the flavour of high grade tobacco is in large meas- 
 ure, or even in part, due to the action of the pe- 
 culiar microbes from the soil where it grows, it 
 ought to be possible to produce similar flavours 
 in the leaves of tobacco grown in other localities, 
 if the fermentation of the leaves is carried on by 
 means of the pure cultures of bacteria obtained 
 from the high grade tobacco. Not very much has 
 been done or is known in this connection as yet. 
 Two bacteriologists have experimented independ- 
 ently in fermenting tobacco leaves by the action 
 of pure cultures of bacteria obtained from such 
 sources. Each of them reports successful experi- 
 ments. Each claims that they have been able to
 
 62 THE STORY OF GERM LIFE. 
 
 improve the quality of tobacco by inoculating the 
 leaves with a pure culture of bacteria obtained 
 from tobacco having high quality in flavour. In 
 addition to this, several other bacteriologists have 
 carried on experiments sufficient to indicate that 
 the flavours of the tobacco and the character of 
 the ripening may be decidedly changed by the use 
 of different species of micro-organisms in the fer- 
 mentations that go on during the curing processes. 
 
 In regard to the whole matter, however, we 
 must recognise that as yet we have very little 
 knowledge. The subject has been under investi- 
 gation for only a short time; and, while consid- 
 erable information has been derived, this infor- 
 mation is not thoroughly understood, and our 
 knowledge in regard to the matter is as yet in 
 rather a chaotic condition. It seems certain, 
 however, that the quality of tobacco is in large 
 measure dependent upon the character of the fer- 
 mentations that occur at different stages of the 
 curing. It seems certain also that these fermen- 
 tations are wholly or chiefly produced by micro- 
 organisms, and that the character of the fermen- 
 tation is in large measure dependent upon the 
 species of micro-organisms that produce it. If 
 these are facts, it would seem not improbable 
 that a further study may produce practical re- 
 sults for this great industry. The study of yeasts 
 and the methods of keeping yeast from contami- 
 nations has revolutionised the brewing industry. 
 Perhaps in this other fermentative industry, which 
 is of such great commercial extent, the use of 
 pure cultures of bacteria may in the future pro- 
 duce as great revolutions in methods as it has in 
 the industry of the alcoholic fermentation. 
 
 It must not, however, be inferred that the dif-
 
 THE USE OF BACTERIA IN THE ARTS. 63 
 
 ferences in grades of tobacco grown in different 
 parts of the world are due solely to variations in 
 the curing processes and to the types of fermen- 
 tation. There are differences in the texture of 
 the leaves, differences in the chemical composi- 
 tion of the tobaccoes, which are due undoubtedly 
 to the soils and the climatic conditions in which 
 they grow, and these, of course, will never be af- 
 fected by changing the character of the ferment- 
 ative processes. It is, however, probable that in 
 so far as the flavours that distinguish the high and 
 low grades of tobacco are due to the character of 
 the fermentative processes, they may be in the fu- 
 ture, at least to a large extent, controlled by the 
 use of pure cultures in curing processes. Seem- 
 ingly, then, there is as great a future in the de- 
 velopment of this fermentative industry as there 
 has been in the past in the development of the 
 fermentative industry associated with brewing 
 and vinting. 
 
 OPIUM. 
 
 Opium for smoking purposes is commonly 
 allowed to undergo a curing process which lasts 
 several months. This appears to be somewhat 
 similar to the curing of tobacco. Apparently it 
 is a fermentation due to the growth of micro- 
 organisms. The organisms in question are not, 
 however, bacteria in this case, but a species of 
 allied fungus. The plant is a mould, and it is 
 claimed that inoculation of the opium with cul- 
 tures of this mould hastens the curing. 
 
 TROUBLESOME FERMENTATIONS. 
 
 Before leaving this branch of the subject it is 
 necessary to notice some of the troublesome fer-
 
 64 THE STORY OF GERM LIFE. 
 
 mentations which are ever interfering with our 
 industries, requiring special methods, or, indeed, 
 sometimes developing special industries to meet 
 them. As agents of decomposition, bacteria will 
 of course be a trouble whenever they get into 
 material which it is desired to preserve. Since 
 they are abundant everywhere, it is necessary to 
 count upon their attacking with certainty any 
 fermentable substance which is exposed to air 
 and water. Hence they are frequently the cause 
 of much trouble. In the fermentative industries 
 they occasionally cause an improper sort of fer- 
 mentation to occur unless care is taken to pre- 
 vent undesired species of bacteria from being 
 present. In vinegar making, improper species of 
 bacteria obtaining access to the solution give 
 rise to undesirable flavours, greatly injuring the 
 product. In tobacco curing it is very common 
 for the wrong species of bacteria to gain access 
 to the tobacco at some stage of the curing and 
 by their growth give rise to various troubles. 
 It is the ubiquitous presence of bacteria which 
 makes it impossible to preserve fruits, meats, or 
 vegetables for any length of time without special 
 methods. This fact in itself has caused the de- 
 velopment of one of our most important indus- 
 tries. Canning meats or fruits consists in noth- 
 ing more than bringing them into a condition in 
 which they will be preserved from attack of these 
 micro-organisms. The method is extremely sim- 
 ple in theory. It is nothing more than heating 
 the material to be preserved to a high tempera- 
 ture and then sealing it hermetically while it is 
 still hot. The heat kills all the bacteria which 
 may chance to be lodged in it, and the hermetical 
 sealing prevents other bacteria from obtaining
 
 THE USE OF BACTERIA IN THE ARTS. 65 
 
 access. Inasmuch as all organic decomposition 
 is produced by bacterial growth, such sterilized 
 and sealed material will be preserved indefinitely 
 when the operation is performed carefully enough. 
 The methods of accomplishing this with sufficient 
 care are somewhat varied in different industries, 
 but they are all fundamentally the same. It is 
 an interesting fact that this method of preserving 
 meats was devised in the last century, before the 
 relation of micro-organisms to fermentation and 
 putrefaction was really suspected. For a long 
 time it had been in practical use while scientists 
 were still disputing whether putrefaction could be 
 avoided by preventing the access of bacteria. The 
 industry has, however, developed wonderfully 
 within the last few years, since the principles 
 underlying it have been understood. This un- 
 derstanding has led to better methods of destroy- 
 ing bacterial life and to proper sealing, and these 
 have of course led to greater success in the pres- 
 ervation, until to-day the canning industries are 
 among those which involve capital reckoned in 
 the millions. 
 
 Occasionally bacteria are of some value in 
 food products. The gamy flavour of meats is 
 nothing more than incipient decomposition. 
 Sauer Kraut is a food mass intentionally allowed 
 to ferment and sour. The value of bacteria in 
 producing butter and cheese flavours is noticed 
 elsewhere. But commonly our aim must be to 
 prevent the growth of bacteria in foods. Foods 
 must be dried or cooked or kept on ice, or some 
 other means adopted for preventing bacterial 
 growth in them. It is their presence that forces 
 us to keep our ice box, thus founding the ice 
 business, as well as that of the manufacture of
 
 66 THE STORY OF GERM LIFE. 
 
 refrigerators. It is their presence, again, that 
 forces us to smoke hams, to salt mackerel, to dry 
 fish or other meats, to keep pork in brine, and to 
 introduce numerous other details in the methods 
 of food preparation and preservation. 
 
 CHAPTER III. 
 
 RELATION OF BACTERIA TO THE DAIRY 
 INDUSTRY. 
 
 DAIRYING is one of the most primitive of our 
 industries. From the very earliest period, ever 
 since man began to keep domestic cattle, he has 
 been familiar with dairying. During these many 
 centuries certain methods of procedure have 
 been developed which produce desired results. 
 These methods, however, have been devised sim- 
 ply from the accumulation of experience, with 
 very little knowledge as to the 'reasons underly- 
 ing them. The methods of past centuries are, 
 however, ceasing to be satisfactory. The ad- 
 vance of our civilization during the last half 
 century has seen a marked expansion in the ex- 
 tent of the dairy industry. With this expansion 
 has appeared the necessity for new methods, and 
 dairymen have for years been looking for them. 
 The last few years have been teaching us that 
 the new methods are to be found along the line 
 of the application of the discoveries of modern 
 bacteriology. We have been learning that the 
 dairyman is more closely related to bacteria and 
 their activities than almost any other class of 
 persons. Modern dairying, apart from the mat-
 
 RELATION OF BACTERIA TO DAIRY INDUSTRY. 67 
 
 ter of keeping the cow, consists largely in trying 
 to prevent bacteria from growing in milk or in 
 stimulating their growth in cream, butter, and 
 cheese. These chief products of the dairy will be 
 considered separately. 
 
 SOURCES OF BACTERIA IN MILK. 
 
 The first fact that claims our attention is, that 
 milk at the time it is secreted from the udder of 
 the healthy cow contains no bacteria. Although 
 bacteria are almost ubiquitous, they are not found 
 in the circulating fluids of healthy animals, and 
 are not secreted by their glands. Milk when 
 first secreted by the milk gland is therefore free 
 from bacteria. It has taken a long time to 
 demonstrate this fact, but it has been finally satis- 
 factorily proved. Secondly, it has been demon- 
 strated that practically all of the normal changes 
 which occur in milk after its secretion are caused 
 by the growth of bacteria. This, too, was long 
 denied, and for quite a number of years after 
 putrefactions and fermentations were generally 
 acknowledged to be caused by the growth of 
 micro-organisms, the changes which occurred in 
 milk were excepted from the rule. The uni- 
 formity with which milk will sour, and the diffi- 
 culty, or seeming impossibility, of preventing this 
 change, led to the belief that the souring of milk 
 was a normal change characteristic of milk, 
 just as clotting is characteristic of blood. This 
 was, however, eventually disproved, and it was 
 finally demonstrated that, beyond a few physi- 
 cal changes connected with evaporation and a 
 slight oxidation of the fat, milk, if kept free 
 from bacteria, will undergo no change. If bac-
 
 68 THE STORY OF GERM LIFE. 
 
 teria are not present, it will remain sweet indefi- 
 nitely. 
 
 But it is impossible to draw milk from the 
 cow in such a manner that it will be free from 
 bacteria except by the use of precautions abso- 
 lutely impracticable in ordinary dairying. As 
 milk is commonly drawn, it is sure to be contami- 
 nated by bacteria, and by the time it has entered 
 the milk pail it contains frequently as many as 
 half a million, or even a million, bacteria in every 
 cubic inch of the milk. This seems almost in- 
 credible, but it has been demonstrated in many 
 cases and is beyond question. Since these bac- 
 teria are not in the secreted milk, they must 
 come from some external sources, and these 
 sources are the following: 
 
 The first in importance is the cow herself; 
 for while her milk when secreted is sterile, and 
 while there are no bacteria in her blood, neverthe- 
 less the cow is the most prolific source of bacte- 
 rial contamination. In the first place, the milk 
 ducts are full of them. After each milking a lit- 
 tle milk is always left in the duct, and this fur- 
 nishes an ideal place for bacteria to grow. Some 
 bacteria from the air or elsewhere are sure to 
 get into these ducts after the milking, and 
 they begin at once to multiply rapidly. By the 
 next milking they become very abundant in the 
 ducts, and the first milk drawn washes most of 
 them at once into the milk pail, where they can 
 continue their growth in the milk. Again, the 
 exterior of the cow's body contains them in 
 abundance. Every hair, every particle of dirt, 
 every bit of dried manure, is a lurking place for 
 millions of bacteria. The hind quarters of a 
 cow are commonly in a condition of much filth,
 
 RELATION OF BACTERIA TO DAIRY INDUSTRY. 69 
 
 for the farmer rarely grooms his cow, and during 
 the milking, by her movements, by the switching 
 of her tail, and by the rubbing she gets from the 
 milker, no inconsiderable amount of this dirt and 
 filth is brushed off and falls into the milk pail. 
 The farmer understands this source of dirt and 
 usually feels it necessary to strain the milk after 
 the milking. But the straining it receives through 
 a coarse cloth, while it will remove the coarser 
 particles of dirt, has no effect upon the bacteria, 
 for these pass through any strainer unimpeded. 
 Again, the milk vessels themselves contain bac- 
 teria, for they are never washed absolutely clean. 
 After the most thorough washing which the milk 
 pail receives from the kitchen, there will always 
 be left many bacteria clinging in the cracks of the 
 tin or in the wood, ready to begin to grow as 
 soon as the milk once more fills the pail. The 
 milker himself contributes to the supply, for he 
 goes to the milking with unclean hands, unclean 
 clothes, and not a few bacteria get from him to 
 his milk pail. Lastly, we find the air of the milk- 
 iig stall furnishing its quota of milk bacteria. 
 This source of bacteria is, however, not so great 
 liS was formerly believed. That the air may con- 
 '.ain many bacteria in its dust is certain, and 
 doubtless these fall in some quantity into the 
 milk, especially if the cattle are allowed to feed 
 upon dusty hay before and during the milking. 
 But unless the air is thus full of dust this source 
 of bacteria is not very great, and compared with 
 the bacteria from the other sources the air bac- 
 teria are unimportant. 
 
 The milk thus gets filled with bacteria, and 
 since it furnishes an excellent food these bacteria 
 begin at once to grow. The milk when drawn is
 
 70 THE STORY OF GERM LIFE. 
 
 warm and at a temperature which especially 
 stimulates bacterial growth. They multiply with 
 great rapidity, and in the course of a few hours 
 increase perhaps a thousandfold. The numbers 
 which may be found after twenty-four hours are 
 sometimes inconceivable ; market milk may con- 
 tain as many as five hundred millions per cubic 
 inch ; and while this is a decidedly extreme num- 
 ber, milk that is a day old will almost always 
 contain many millions in each cubic inch, the 
 number depending upon the age of the milk and 
 its temperature. During this growth the bacteria 
 have, of course, not been without their effect. 
 Recognising as we do that bacteria are agents for 
 chemical change, we are prepared to see the milk 
 undergoing some modifications during this rapid 
 multiplication of bacteria. The changes which 
 these bacteria produce in the milk and its prod- 
 ucts are numerous, and decidedly affect its value. 
 They are both advantageous and disadvantageous 
 to the dairyman. They are nuisances so far as 
 concerns the milk producer, but allies of the but- 
 ter and cheese maker. 
 
 THE EFFECT OF BACTERIA ON MILK. 
 
 The first and most universal change effected 
 in milk is its souring. So universal is this phe- 
 nomenon that it is generally regarded as an in- 
 evitable change which can not be avoided, and, as 
 already pointed out, has in the past been regarded 
 as a normal .property of milk. To-day, however, 
 the phenomenon is well understood. It is due to 
 the action of certain of the milk bacteria upon 
 the milk sugar which converts it into lactic acid, 
 and this acid gives the sour taste and curdles
 
 RELATION OF BACTERIA TO DAIRY INDUSTRY. 71 
 
 the milk. After this acid is produced in small 
 quantity its presence proves deleterious to the 
 growth of the bacteria, and further bacterial 
 growth is checked. After souring, therefore, the 
 milk for some time does not ordinarily undergo 
 any further changes. 
 
 Milk souring has been commonly regarded as 
 a single phenomenon, alike in all cases. When it 
 was first studied by bacteriologists it was thought 
 to be due in all cases to a single species of micro- 
 organism which was discovered to 
 be commonly present and named 
 Bacillus acidi lactici (Fig. 19). This | 
 bacterium has certainly the power jji 
 
 Bacillus acidi lactici (Fig. 19). This 
 
 found to be very common in dai- 
 ries in Europe. As soon as bacte- FlG 
 riologists turned their attention acidi lactici, tt& 
 more closely to the subject it was ofT^miLk" 156 
 found that the spontaneous sour- 
 ing of milk was not always caused by the same 
 species of bacterium. Instead of finding this Ba- 
 cillus acidi lactici always present, they found that 
 quite a number of different species of bacteria 
 have the power of souring milk, and are found in 
 different specimens of soured milk. The number 
 of species of bacteria which have been found to 
 sour milk has increased until something over a 
 hundred are known to have this power. These 
 different species do not affect the milk in the 
 same way. All produce some acid, but they 
 differ in the kind and the amount of acid, and 
 especially in the other changes which are effected 
 at the same time that the milk is soured, so that 
 the resulting soured milk is quite variable. In 
 spite of this variety, however, the most recent
 
 72 THE STORY OF GERM LIFE. 
 
 work tends to show that the majority of cases of 
 spontaneous souring of milk are produced by 
 bacteria which, though somewhat variable, prob- 
 ably constitute a single species, and are identical 
 with the Bacillus acidi lactici (Fig. 19). This spe- 
 cies, found common in the dairies of Europe, ac- 
 cording to recent investigations occurs in this 
 country as well. We may say, then, that while 
 there are many species of bacteria infesting the 
 dairy which can sour the milk, there is one which 
 is more common and more universally found than 
 others, and this is the ordinary cause of milk 
 souring. 
 
 When we study more carefully the effect upon 
 the milk of the different species of bacteria found 
 in the dairy, we find that there is a great variety 
 of changes which they produce when they are al- 
 lowed to grow in milk. The dairyman expe- 
 riences many troubles with his milk. It sometimes 
 curdles without becoming acid. Sometimes it 
 becomes bitter , or acquires an unpleasant " tainted" 
 taste, or, again, a "soapy" taste. Occasionally a 
 dairyman finds his milk becoming slimy, instead of 
 souring and curdling in the normal fashion. At 
 such times, after a number of hours, the milk be- 
 comes so slimy that it can be drawn into long 
 threads. Such an infection proves very trouble- 
 some, for many a time it persists in spite of all 
 attempts made to remedy it. Again, in other 
 cases the milk will turn blue, acquiring about the 
 time it becomes sour a beautiful sky-blue colour. 
 Or it may become red, or occasionally yellow. All 
 of these troubles the dairyman owes to the pres- 
 ence in his milk of unusual species of bacteria 
 which grow there abundantly. 
 
 Bacteriologists have been able to make out
 
 RELATION OF BACTERIA TO DAIRY INDUSTRY. 73 
 
 satisfactorily the connection of all these infec- 
 tions with different species of the bacteria. A 
 large number of species have been found to cur- 
 dle milk without rendering it acid, several render 
 it bitter, and a number produce a 
 " tainted " and one a " soapy " 
 taste. A score or more have been 
 found which have the power of 
 rendering the milk slimy. Two 
 different species at least have the 
 power of turning the milk to sky- FIG. 20. Dairybac- 
 blue colour; two or three pro- redTiik r0dUdng 
 duce red pigments (Fig. 20), and 
 one or two have been found which produce a yel- 
 low colour. In short, it has been determined be- 
 yond question that all these infections, which are 
 more or less troublesome to dairymen, are due 
 to the growth of unusual bacteria in the milk. 
 
 These various infections are all troublesome, 
 and indeed it may be said that, so far as concerns 
 the milk producer and the milk consumer, bac- 
 teria are from beginning to end a source of trou- 
 ble. It is the desire of the milk producer to 
 avoid them as far as possible a desire which is 
 shared also by everyone who has anything to do 
 with milk as milk. Having recognised that the 
 various troubles, which occasionally occur even 
 in the better class of dairies, are due to bacteria, 
 the dairyman is, at least in a measure, prepared 
 to avoid them. The avoiding of these troubles 
 is moderately easy as soon as dairymen recog- 
 nise the source from which the infectious or- 
 ganisms come, and also the fact that low tem- 
 peratures will in all cases remedy the evil to a 
 large extent. With this knowledge in hand the 
 avoidance of all these troubles is only a question
 
 74 THE STORY OF GERM LIFE. 
 
 of care in handling the dairy. It must be recog- 
 nised that most of these troublesome bacteria 
 come from some unusual sources of infection. 
 By unusual sources are meant those which the ex- 
 ercise of care will avoid. It is true that the sour- 
 ing bacteria appear to be so universally distrib- 
 uted that they can not be avoided by any ordinary 
 means. But all other troublesome bacteria ap- 
 pear to be within control. The milkman must 
 remember that the sources of the troubles which 
 are liable to arise in his milk are in some form of 
 filth : either filth on the cow, or dust in the hay 
 which is scattered through the barn, or dirt on 
 cows' udders, or some other unusual and avoid- 
 able source. These sources, from what we have 
 already noticed, will always furnish the milk with 
 bacteria; but under common conditions, and when 
 the cow is kept in conditions of ordinary cleanli- 
 ness, and frequently even when not cleanly, will 
 only furnish bacteria that produce the universal 
 souring. Recognising this, the dairyman at once 
 learns that his remedies for the troublesome in- 
 fections are cleanliness and low temperatures. 
 If he is careful to keep his milk vessels scrupu- 
 lously clean ; if he will keep his cow as cleanly as 
 he does his horse; and if he will use care in and 
 around the barn and dairy, and then apply low 
 temperatures to the milk, he need never be dis- 
 turbed by slimy or tainted milk, or any of these 
 other troubles; or he can remove such infections 
 speedily should they once appear. Pure sweet 
 milk is only a question of sufficient care. But 
 care means labour and expense. As long as we 
 demand cheap milk, so long will we be supplied 
 with milk procured under conditions of filth. But 
 when we learn that cheap milk is poor milk, and
 
 RELATION OF BACTERIA TO DAIRY INDUSTRY. 75 
 
 when we are willing to pay a little more for it, 
 then only may we expect the use of greater care 
 in the handling of the milk, resulting in a purer 
 product. 
 
 Bacteriology has therefore taught us that the 
 whole question of the milk supply in our com- 
 munities is one of avoiding the too rapid growth 
 of bacteria. These organisms are uniformly a 
 nuisance to the milkman. To avoid their evil 
 influence have been designed all the methods of 
 caring for the dairy and the barn, all the methods 
 of distributing milk in ice cars. Moreover, all the 
 special devices connected with the great industry 
 of milk supply have for their foundation the at- 
 tempt to avoid, in the first place, the presence of 
 too great a number of bacteria, and, in the second 
 place, the growth of these bacteria. 
 
 BACTERIA IN BUTTER MAKING. 
 
 Cream ripening. Passing from milk to butter, 
 we find a somewhat different story, inasmuch as 
 here bacteria are direct allies to the dairyman 
 rather than his enemies. Without being aware of 
 it, butter makers have for years been making use 
 of bacteria in their butter making and have been 
 profiting by the products which the bacteria have 
 furnished them. Cream, as it is obtained from 
 milk, will always contain bacteria in large quan- 
 tity, and these bacteria will grow as readily in 
 the cream as they will in the milk. The butter 
 maker seldom churns his cream when it is freshly 
 obtained from the milk. There are, it is true, 
 some places where sweet cream butter is made 
 and is in demand, but in the majority of butter- 
 consuming countries a different quality of butter
 
 76 THE STORY OF GERM LIFE. 
 
 is desired, and the cream is subjected to a process, 
 known as "ripening" or "souring" before it is 
 churned. In ripening, the cream is simply al- 
 lowed to stand in a vat for a period varying 
 from twelve hours to two or three days, accord- 
 ing to circumstances. During this period certain 
 changes take place therein. The bacteria which 
 were in the cream originally, get an opportunity 
 to grow, and by the time the ripening is complete 
 they become extremely numerous. As a result, 
 the character of the cream changes just as the 
 milk is changed under similar circumstances. It 
 becomes somewhat soured; it becomes slightly 
 curdled, and acquires a peculiarly pleasant taste 
 and an aroma which was not present in the origi- 
 nal fresh cream. After this ripening the cream 
 is churned. It is during the ripening that the 
 bacteria produce their effect, for after the churn- 
 ing they are of less importance. Part of them 
 collect in the butter, part of them are washed off 
 from the butter in the buttermilk and the subse- 
 quent processes. Most of the bacteria that are 
 left ifi the butter soon die, not finding there a 
 favourable condition for growth ; some of them, 
 however, live and grow for some time and are 
 prominent agents in the changes by which butter 
 becomes rancid. The butter maker is concerned 
 with the ripening rather than with later processes. 
 The object of the ripening of cream is to render 
 it in a better condition for butter making. The 
 butter maker has learned by long experience that 
 ripened cream churns more rapidly than sweet 
 cream, and that he obtains a larger yield of butter 
 therefrom. The great object of the ripening, 
 however, is to develop in the butter the peculiar 
 flavour and aroma which is characteristic of the
 
 RELATION OF BACTERIA TO DAIRY INDUSTRY. 77 
 
 highest product. Sweet cream butter lacks fla- 
 vour and aroma, having indeed a taste almost 
 identically the same as cream. Butter, however, 
 that is made from ripened cream has a peculiar 
 delicate flavour and aroma which is well known to 
 lovers of butter, and which is developed during 
 the ripening process. 
 
 Bacteriologists have been able to explain with 
 a considerable degree of accuracy the object of 
 this ripening. The process is really a fermenta- 
 tion comparable to the fermentation that takes 
 place in a brewer's malt. The growth of bacteria 
 during the ripening produces chemical changes 
 of a somewhat complicated character, and con- 
 cerns each of the ingredients of the milk. The 
 lactic-acid organisms affect the milk sugar and 
 produce lactic acid ; others act upon the fat, pro- 
 ducing slight changes therein; while others act 
 upon the casein and the albumens of the milk. 
 As a result, various biproducts of decomposition 
 arise, and it is these biproducts of decomposition 
 that make the difference between the ripened and 
 the unripened cream. They render it sour and 
 curdle it, and they also produce the flavours and 
 aromas that characterize it. Products of decom- 
 position are generally looked upon as undesirable 
 for food, and this is equally true of these products 
 that arise in cream if the decomposition is allowed 
 to continue long enough. If the ripening, instead 
 of being stopped at the end of a day or two, is 
 allowed to continue several days, the cream be- 
 comes decayed and the butter made therefrom is 
 decidedly offensive. But under the conditions of 
 ordinary ripening,, when the process is stopped at 
 the right moment, the decomposition products 
 are pleasant rather than unpleasant, and the fla/- 
 G
 
 7 8 THE STORY OF GERM LIFE. 
 
 vours and aromas which they impart to the cream 
 and to the subsequent butter are those that are 
 desired. It is these decomposition products that 
 give the peculiar character to a high quality of 
 butter, and this peculiar quality is a matter that 
 determines the price which the butter maker can 
 obtain for his product. 
 
 But, unfortunately, the butter maker is not al- 
 ways able to depend upon the ripening. While 
 commonly it progresses in a satisfactory manner, 
 sometimes, for no reason that he can assign, the 
 ripening does not progress normally. Instead of 
 developing the pleasant aroma and flavour of the 
 properly ripened cream, the cream develops un- 
 pleasant tastes. It may be bitter or somewhat 
 tainted, and just as sure as these flavours develop 
 in the cream, so sure does the quality of the but- 
 ter suffer. Moreover, it has been learned by ex- 
 perience that some creameries are incapable of 
 obtaining an equally good ripening of their cream. 
 While some of them will obtain favourable results, 
 others, with equal care, will obtain a far less favour- 
 able flavour and aroma in their butter. The rea- 
 son for all this has been explained by modern bacte- 
 riology. In the milk, and consequently in the 
 cream, there are always found many bacteria, but 
 these are not always of the same kinds. There 
 are scores, and probably hundreds, of species of 
 bacteria common in and around our barns and 
 dairies, and the bacteria that are abundant and 
 that grow in different lots of cream will not be 
 always the same. It makes a decided difference 
 in the character of the ripening, and in the conse- 
 quent flavours and aromas, whether one or another 
 species of bacteria has been growing in the cream. 
 Some species are found to produce good results
 
 RELATION OF BACTERIA TO DAIRY INDUSTRY. 79 
 
 with desired flavours, while others, under identical 
 conditions, produce decidedly poor results with 
 undesired flavours (Figs. 21-23). If tne butter 
 maker obtains cream which is filled with a large 
 number of bacteria capable of producing good 
 flavours, then the ripening of his cream will be 
 satisfactory and his butter will be of high quality. 
 If, however, it chances that his cream contains 
 only the species which produce unpleasant fla- 
 vours, then the character of the ripening will be 
 decidedly inferior and the butter will be of a 
 poorer grade. Fortunately the majority of the 
 kinds of bacteria liable to get into the cream 
 from ordinary sources are such as produce either 
 good effects upon the cream or do not materially 
 influence the flavour or aroma. Hence it is that 
 the ripening of cream will commonly produce 
 good results. Bacteriologists have learned that 
 there are some species of bacteria more or less 
 common around our barns which produce unde- 
 sirable effects upon flavour, and should these be- 
 come especially abundant in the cream, then the 
 character of the ripening and the quality of the 
 subsequent butter will suffer. These malign spe- 
 cies of bacteria, however, are not very common in 
 properly kept barns and dairies. Hence the pro- 
 cess that is so widely used, of simply allowing 
 cream to ripen under the influence of any bacte- 
 ria that happen to be in it, ordinarily produces 
 good results. But our butter makers sometimes 
 find, at the times when the cattle change from 
 winter to summer or from summer to winter feed, 
 that the ripening is abnormal. The reason ap- 
 pears to be that the cream has become infested 
 with an abundance of malign species. The ripen- 
 ing that they produce is therefore an undesirable
 
 8o THE STORY OF GERM LIFE. 
 
 one, and the quality of the butter is sure to 
 
 surfer. 
 
 So long as butter was made only in private 
 
 dairies it was a matter of comparatively little 
 
 importance if there was an occasional falling off 
 in quality of this sort. When 
 it was made a few pounds 
 at a time, and only once or 
 twice a week, it was not a 
 very serious matter if a few 
 churnings of butter did suf- 
 fer in quality. But to-day 
 the butter-making industries 
 
 FIG. 2i. Dairy bacterium are becoming more and more 
 ^r^b^eT^s concentrated into large 
 
 species has been used creameries, and It IS a mat- 
 commercially for the rip- ter o f a good dea l more j m _ 
 ening of cream. , . 
 
 portance to discover some 
 
 means by which a uniformly high quality can be 
 insured. If a creamery which makes five hun- 
 dred pounds of butter per day surfers from such 
 an injurious ripening, the quality of its but- 
 ter will fall off to such an extent as to command 
 a lower price, and the creamery suffers material- 
 ly. Perhaps the continuation of such a trouble 
 for two or three weeks would make a difference 
 between financial success and failure in the cream- 
 ery. With our concentration of the butter-mak- 
 ing industries it is becoming thus desirable to 
 discover some means of regulating this process 
 more accurately. 
 
 The remedy of these occasional ill effects in 
 cream ripening has not been within the reach of 
 the butter maker. The butter maker must make 
 butter with the cream that is furnished him, and 
 if that cream is already impregnated with malign
 
 RELATION OF BACTERIA TO DAIRY INDUSTRY. 8 1 
 
 species of bacteria he is helpless. It is true that 
 much can be done to remedy these difficulties by 
 the exercise of especial care in the barns of the 
 patrons of the creamery. If the barns, the cows, 
 the dairies, the milk vessels, etc., are all kept in 
 condition of strict cleanliness, if especial care is 
 taken particularly at the seasons 
 of the year when trouble is likely 
 to arise, and if some attention is 
 paid to the kind of food which the & 
 cattle eat, as a rule the cream will 
 not become infected with injurious FIG. 22. Dairy 
 bacteria. It may be taken as a JSj^JS 
 demonstrated fact that these ma- aroma in butter, 
 lign bacteria come from sources of 
 filth, and the careful avoidance of all such sources 
 of filth will in a very large measure prevent their 
 occurrence in the cream. Such measures as these 
 have been found to be practicable in many cream- 
 eries. Creameries which make the highest priced 
 and the most uniform quality of butter are those 
 in which the greatest care is taken in the barns 
 and dairies to insure cleanliness and in the han- 
 dling of the milk and cream. With such attention 
 a large portion of the trouble which arises in the 
 creameries from malign bacteria may be avoided. 
 But these methods furnish no sure remedy 
 against evils of improper species of bacteria in 
 cream ripening, and do not furnish any sure 
 means of obtaining uniform flavour in butter. 
 Even under the very best conditions the flavour 
 of the butter will vary with the season of the 
 year. Butter made in the winter is inferior to 
 that made in the summer months ; and while this 
 is doubtless due in part to the different food 
 which the cattle have and to the character of the
 
 82 THE STORY OF GERM LIFE. 
 
 cream resulting therefrom, these differences in 
 the flavour of the butter are also in part depend- 
 ent upon the different species of bacteria which 
 are present in the ripening of cream at different 
 seasons. The species of bacteria in June cream 
 are different from those that are commonly pres- 
 ent in January cream, and this is certainly a fac- 
 tor in determining the difference between winter 
 and summer butter. 
 
 USE OF ARTIFICIAL BACTERIA CULTURES FOR 
 CREAM RIPENING. 
 
 Bacteriologists have been for some time en- 
 deavouring to aid butter makers in this direction 
 by furnishing them with the bacteria needful for 
 the best results in cream ripening. The method 
 of doing this is extremely simple in principle, but 
 proves to be somewhat difficult in practice. It is 
 only necessary to obtain the species of bacteria 
 that produce the highest results, and then to fur- 
 nish these in pure culture and in large quantity 
 to the butter makers, to enable them to inocu- 
 late their cream with the species of bacteria 
 which will produce the results that they desire. 
 For this purpose bacteriologists have been for 
 several years searching for the proper species of 
 bacteria to produce the best results, and there 
 have been put upon the market for sale several 
 distinct " pure cultures " for this purpose. These 
 have been obtained by different bacteriologists 
 and dairymen in the northern European countries 
 and also in the United States. These pure cul- 
 tures are furnished to the dairymen in various 
 forms, but they always consist of great quanti- 
 ties of certain kinds of bacteria which experience
 
 RELATION OF BACTERIA TO DAIRY INDUSTRY. 83 
 
 has found to be advantageous for the purpose of 
 cream ripening (Figs. 21-23). 
 
 There have hitherto appeared a number of 
 difficulties in the way of reaching complete suc- 
 cess in these directions. The most prominent 
 arises in devising a method of 
 using pure cultures in the 
 creamery. The cream which 
 the butter makers desire to 
 ripen is, as we have seen, al- 
 ready impregnated with bac- 
 teria, and would ripen in a 
 fashion of its own even if no 
 pure culture of bacteria were FlG - 23. Dairy bacteri- 
 added thereto. Pure cultures SfiStStfi? 
 can not therefore be used as 
 simply as can yeast in bread dough. It is plain 
 that the simple addition of a pure culture to a mass 
 of cream would not produce the desired effects, 
 because the cream would be ripened then, not by 
 the pure culture alone, but by the pure culture 
 plus all of the bacteria that were originally pres- 
 ent. It would, of course, be something of a ques- 
 tion as to whether under these conditions the 
 results would be favourable, and it would seem 
 that this method would not furnish any means of 
 getting rid of bad tastes and flavours which have 
 come from the presence of malign species of bac- 
 teria. It is plainly desirable to get rid of the 
 cream bacteria before the pure culture is added. 
 This can be readily done by heating it to a tem- 
 perature of 69 C. (155 F.) for a short time, this 
 temperature being sufficient to destroy most of 
 the bacteria. The subsequent addition of the 
 pure culture of cream-ripening bacteria will cause 
 the cream to ripen under the influence of the add-
 
 84 THE STORY OF GERM LIFE. 
 
 ed culture alone. This method proves to be suc- 
 cessful, and in the butter-making countries in 
 Europe it is becoming rapidly adopted. 
 
 In this country, however, this process has 
 not as yet become very popular, inasmuch as the 
 heating of the cream is a matter of considerable 
 expense and trouble, and our butter makers have 
 not been very ready to adopt it. For this reason, 
 and also for the purpose of familiarizing butter 
 makers with the use of pure cultures, it has been 
 attempted to produce somewhat similar though 
 less uniform results by the use of pure cultures 
 in cream without previous healing. In the use 
 of pure cultures in this way, the butter maker is 
 directed to add to his cream a large amount of 
 a prepared culture of certain species of bacteria, 
 upon the principle that the addition of such a 
 large number of bacteria to the cream, even 
 though the cream is already inoculated with 
 certain bacteria, will produce a ripening of the 
 cream chiefly influenced by the artificially added 
 culture. The culture thus added, being present 
 in very much greater quantity than the other 
 "wild" species, will have a much greater effect 
 than any of them. This method, of course, can- 
 not insure uniformity. While it may work satis- 
 factorily in many cases, it is very evident that in 
 others, when the cream is already filled with a 
 large number of malign species of bacteria, such 
 an artificial culture would not produce the desired 
 results. This appears to be not only the theo- 
 retical but the actual experience, The addition 
 of such pure cultures in many cases produces 
 favourable results, but it does not always do so, 
 and the result is not uniform. While the use of 
 pure cultures in this way is an advantage over
 
 RELATION OF BACTERIA TO DAIRY INDUSTRY. 85 
 
 the method of simply allowing the cream to ripen 
 normally without such additions, it is a method 
 that is decidedly inferior to that which first 
 pasteurizes the cream and subsequently adds a 
 starter. 
 
 There is still another method of adding bac- 
 teria to cream to insure a more advantageous 
 ripening, which is frequently used, and, being 
 simpler, is in many cases a decided advantage. 
 This method is by the use of what is called a 
 natural starter. A natural starter consists simply 
 of a lot of cream which has been taken from the 
 most favourable source possible that is, from 
 the cleanest and best dairy, or from the herd 
 producing the best quality of cream and allow- 
 ing this cream to stand in a warm place for a 
 couple of days until it becomes sour. The cream 
 will by that time be filled with large numbers of 
 bacteria, and this is then put as a starter into the 
 vat of cream to be ripened. Of course, in the use 
 of this method the butter maker has no control 
 over the kinds of bacteria that will grow in the 
 starter, but it is found, practically, that if the 
 cream is taken from a good source the results 
 are extremely favourable, and there is produced 
 in this way almost always an improvement in the 
 butter. 
 
 The use of pure cultures is still quite new, 
 particularly in this country. In the European 
 butter-making countries they have been used for 
 a longer period and have become very much bet- 
 ter known. What the future may develop along 
 this line it is difficult to say ; but it seems at 
 least probable that as the difficulties in the de- 
 tails are mastered the time will come when start- 
 ers will be used by our butter makers for theif
 
 86 THE STORY OF GERM LIFE. 
 
 cream ripening, just as yeast is used by house- 
 wives for raising bread, or by brewers for fer- 
 menting malt. These starters will probably in 
 time be furnished by bacteriologists. Bacteriol- 
 ogy, in other words, is offering in the near future 
 to our butter makers a method of controlling the 
 ripening of the cream in such a way as to insure 
 the obtaining of a high and uniform quality of 
 butter, so far, at least, as concerns flavour and 
 aroma. 
 
 BACTERIA IN CHEESE. 
 
 Cheese ripening. The third great product of 
 the dairy industry is cheese, and in connection 
 with this product the dairyman is even more de- 
 pendent upon bacteria than he is in the produc- 
 tion of butter. In the manufacture of cheese the 
 casein of the milk is separated from the other 
 products by the use of rennet, and is collected 
 in large masses and pressed, forming the fresh 
 cheese. This cheese is then set aside for sev- 
 eral weeks, and sometimes for months, to under- 
 go a process that is known as ripening. During 
 the ripening there are developed in the cheese the 
 peculiar flavours which are characteristic of the 
 completed product. The taste of freshly made 
 cheese is extremely unlike that of the ripened 
 product. While butter made from unripened 
 cream has a pleasant flavour, and one which is 
 in many places particularly enjoyed, there is no- 
 where a demand for unripened cheese, for the 
 freshly made cheese has a taste that scarce any 
 one regards as pleasant. Indeed, the whole value 
 of the cheese is dependent upon the flavour of 
 the product, and this flavour is developed during 
 the ripening.
 
 RELATION OF BACTERIA TO DAIRY INDUSTRY. 87 
 
 The cheese maker finds in the ripening of his 
 cheese the most difficult part of his manufacture. 
 It is indeed a process over which he has very 
 little control. Even when all conditions seem to 
 be correct, when cheese is made in the most care- 
 ful manner, it not infrequently occurs that the 
 ripening takes place in a manner that is entire- 
 ly abnormal, and the resulting cheese becomes 
 worthless. The cheese maker has been at an en- 
 tire loss to understand these irregularities, nor 
 has he possessed any means of removing them 
 The abnormal ripening that occurs takes on vari- 
 ous types. Sometimes the cheese will become 
 extraordinarily porous, filled with large holes 
 which cause the cheese to swell out of proper 
 shape and become worthless. At other times, 
 various spots of red or blue appear in the manu- 
 factured cheese; while again unpleasant tastes 
 and flavours develop which render the product of 
 no value. Sometimes a considerable portion of 
 the product of the cheese factory undergoes such 
 irregular ripening, and the product for a long 
 time will thus be worthless. If some means 
 could be discovered of removing these irregu- 
 larities it would be a great boon to the cheese 
 manufacturer; and very many attempts have 
 been made in one way or another to furnish the 
 cheese maker with some details in the manufac- 
 ture which will enable him in a measure to con- 
 trol the ripening. 
 
 The ripening of the cheese has been subjected 
 to a large amount of study on the part of bac- 
 teriologists who have been interested in dairy 
 products. That the ripening of cheese is the 
 result of bacterial growth therein appears to be 
 probable from a priori grounds. Like the ripen-
 
 88 THE STORY OF GERM LIFE. 
 
 ing of cream, it is a process that occurs some- 
 what slowly. It is a chemical change which is 
 accompanied by the destruction of proteid mat- 
 ter; it takes place best at certain temperatures, 
 and temperatures which we know are favourable 
 to the growth of micro-organisms, all of which 
 phenomena suggest to us the action of bacteria. 
 Moreover, the flavours and the tastes that arise 
 have a decided resemblance in many cases to the 
 decomposition products of bacteria, strikingly so 
 in Limburger cheese. When we come to study 
 the matter of cheese ripening carefully we learn 
 beyond question that this a priori conclusion is 
 correct. The ripening of any cheese is depend- 
 ent upon several different factors. The method 
 of preparation, the amount of water left in the 
 curd, the temperature of ripening, and other mis- 
 cellaneous factors connected with the mechanical 
 process of cheese manufacture, affect its charac- 
 ter. But, in addition to all these factors, there is 
 undoubtedly another one, and that is the number 
 and the character of the bacteria that chance to 
 be in the curd when the cheese is made. While it 
 is found that cheeses which are treated by different 
 processes will ripen in a different manner, it is also 
 found that two cheeses which have been made 
 under similar conditions and treated in identically 
 the same way may also ripen in a different manner, 
 so that the resulting flavour will vary. The varia- 
 tions between cheeses thus made may be slight 
 or they may be considerable, but variations cer- 
 tainly do occur. Every one knows the great dif- 
 ference in flavours of different cheeses, and these 
 flavours are due in considerable measure to fac- 
 tors other than the simple mechanical process of 
 making the cheese. The general similarity of
 
 RELATION OF BACTERIA TO DAIRY INDUSTRY. 89 
 
 the whole process to a bacterial fermentation 
 leads us to believe at the outset that some of 
 the differences in character are due to different 
 kinds of bacteria that multiply in the cheese and 
 produce decomposition therein. 
 
 When the matter comes to be studied by bac- 
 teriology, the demonstration of this position be- 
 comes easy. That the ripening of cheese is due 
 to growth of bacteria is very easily proved by 
 manufacturing cheeses from milk which is de- 
 prived of bacteria. For instance, cheeses have 
 been made from milk that has been either ster- 
 ilized or pasteurized which processes destroy 
 most of the bacteria therein and, treated other- 
 wise in a normal manner, are set aside to ripen. 
 These cheeses do not ripen, but remain for months 
 with practically the same taste that they had 
 originally. In other experiments the cheese has 
 been treated with a small amount of disinfective, 
 which is sufficient to prevent bacteria from grow- 
 ing, and again ripening is found to be absolutely 
 prevented. Furthermore, if the cheese under or- 
 dinary conditions is studied during the ripening 
 process, it is found that bacteria are growing dur- 
 ing the whole time. These facts all taken to- 
 gether plainly prove that the ripening of cheese 
 is a fermentation due to bacteria. It will be 
 noticed, however, that the conditions in the 
 cheese are not favourable for very rapid bac- 
 terial growth. It is true that there is plenty 
 of food in the cheese for bacterial life, but the 
 cheese is not very moist; it is extremely dense, 
 being subjected in all cases to more or less pres- 
 sure. The penetration of oxygen into the centre 
 of the mass must be extremely slight. The dens- 
 ity, the lack of a great amount of moisture, and
 
 po THE STORY OF GERM LIFE. 
 
 the lack of oxygen furnish conditions in which 
 bacteria will not grow very rapidly. The condi- 
 tions are far less favourable than those of ripen- 
 ing cream, and the bacteria do not grow with 
 anything like the rapidity that they grow in 
 cream. Indeed, the growth of these organisms 
 during the ripening is extremely slow compared 
 to the possibilities of bacterial growth that we 
 have already noticed. Nevertheless, the bacteria 
 do multiply in the cheese, and as the ripening 
 goes on they become more and more abundant, 
 although the number fluctuates, rising and falling 
 under different conditions. 
 
 When the attempt is made to determine the 
 relation of the different kinds of ripening to dif- 
 ferent kinds of bacteria, it has thus far met with 
 extremely little success. That different flavours 
 are due to the ripening produced by different 
 kinds of bacteria would appear to be almost cer- 
 tain when we remember, as we have already no- 
 ticed, the different kinds of decomposition pro- 
 duced by different species of bacteria. It would 
 seem, moreover, that it ought not to be very diffi- 
 cult 'to separate from the ripened cheese the bac- 
 teria which are present, and thus obtain the kind 
 of bacteria necessary to produce the desired ripen- 
 ing. But for some reason this does not prove to 
 be so easy in practice as it seems to be in theory. 
 Many different species of bacteria have been sep- 
 arated from cheeses. One bacteriologist, studying 
 several cheeses, separated about eighty different 
 species therefrom, and others have found perhaps 
 as many more from different sources. More- 
 over, experiments have been made with a consid- 
 erable number of these different kinds of bacteria 
 to determine whether they are capable of produc-
 
 RELATION OF BACTERIA TO DAIRY INDUSTRY. 91 
 
 ing normal ripening. These experiments consist 
 of making cheese out of milk that has been de- 
 prived of its bacteria, and which has been inocu- 
 lated with large quantities of the species in ques- 
 tion. Hitherto these experiments have not been 
 very satisfactory. In some cases the cheese ap- 
 pears to ripen scarcely at all ; in other cases the 
 ripening occurs, but the resulting cheese is of a 
 peculiar character, entirely unlike the cheese that 
 it is desired to imitate. There have been one or 
 two experiments in recent times that give a little 
 more promise of success than the earlier ones, for 
 a few species of bacteria have been used in ripen- 
 ing with what the authors have thought to be 
 promising success. The cheese made from the 
 milk artificially inoculated with these species 
 ripens in a satisfactory manner and gives some 
 of the character desired, though up to the pres- 
 ent time in no case has the typical normal ripen- 
 ing been produced in any of these experiments. 
 
 But these experiments have demonstrated be- 
 yond question that the abnormal ripening which 
 is common in cheese factories is due to the pres- 
 ence of undesirable species of bacteria in the milk. 
 Many of the experiments in making cheeses by 
 means of artificial cultures of bacteria have re- 
 sulted in decidedly abnormal cheeses. Many of 
 the cheeses thus manufactured have shown imper- 
 fections in ripening which are identical with those 
 actually occurring in the cheese factory. Sev- 
 eral different species of bacteria have been found 
 which, when artificially used thus for ripening 
 cheese, will give rise to the porosity and the ab- 
 normal swelling of the cheese already referred to 
 (Fig. 24). Others produced bad tastes and fla- 
 vours, and enough has been done in this line to
 
 92 THE STORY OF GERM LIFE. 
 
 demonstrate beyond peradventure that the ab- 
 normal ripening of cheese is due primarily to the 
 growth of improper species therein. Quite a long 
 list of species of bacteria which produce abnormal 
 ripening have been isolated 
 from cheeses, and have 
 been studied and experi- 
 mented with by bacteriolo- 
 gists. As a result of this 
 study of abnormal ripening, 
 there has been suggested a 
 method of partially con- 
 
 FIG. *4. Dairy bacterium trolling these remedying 
 'swelled" them. The method con- 
 sists simply in testing the 
 fermenting qualities of the milk used. A small 
 sample of milk from different dairies is allowed to 
 stand in the cheese factory by itself until it un- 
 dergoes its normal souring. If the fermentation 
 or souring that thus occurs is of a normal charac- 
 ter, the milk is regarded as proper for cheese 
 making. But if the fermentation that occurs in 
 any particular sample of milk is unusual; if an 
 extraordinary amount of gas bubbles are pro- 
 duced, or if unpleasant smells and tastes arise, 
 the sample is regarded as unfavourable for cheese 
 making, and as likely to produce abnormal ripen- 
 ing in the cheeses. Milk from this source would 
 therefore be excluded from the milk that is to be 
 used in cheese making. This, of course, is a ten- 
 tative and an unsatisfactory method of control- 
 ling the ripening, and yet it is one of some prac- 
 tical value to cheese makers. It is the only 
 method that has yet been suggested of control- 
 ling the ripening. 
 
 Our bacteriologists, of course, are quite con-
 
 RELATION OF BACTERIA TO DAIRY INDUSTRY. 93 
 
 fident that in the future more practical results 
 will be obtained along this line than in the past. 
 If it is true that cheeses are ripened by bacteria; 
 if it is true that different qualities in the cheese 
 are due to the growth of different species of bac- 
 teria during the ripening, it would seem to be 
 possible to obtain the proper kind of bacteria 
 and to furnish them to the cheese maker for arti- 
 ficially inoculating his cheese, just as it has been 
 possible to furnish artificially cultivated yeasts to 
 the brewer, and as it has become possible to fur- 
 nish artificially cultivated bacteria to the butter 
 maker. We must, however, recognise this to be 
 a matter for the future. Up to the present time 
 no practical results along the lines of bacteria 
 have been obtained which our cheese manufac- 
 turers can make use of in the way of controlling 
 with any accuracy this process of cheese ripening. 
 Thus it will be seen that in this last dairy 
 product bacteria play even a more important part 
 than in any of the others. The food value of 
 cheese is dependent upon the casein which is pres- 
 ent. The market price, however, is controlled 
 entirely by the flavour, and this flavour is a prod- 
 uct of bacterial growth. Upon the action of 
 bacteria, then, the cheese maker is absolutely de- 
 pendent ; and when our bacteriologists are able in 
 the future to investigate this matter further, it 
 seems to be at least possible that they may obtain 
 some means of enabling the cheese maker to con- 
 trol the ripening accurately. Not only so, but 
 recognising the great variety in the flavours of 
 cheese, and recognising that different kinds of 
 bacteria undoubtedly produce different kinds of 
 decomposition products, it seems to be at least 
 possible that a time will come when the cheese 
 7
 
 94 THE STORY OF GERM LIFE. 
 
 maker will be able to produce at will any particu- 
 larly desired flavour in his cheese by the addition 
 to it of particular species of bacteria, or particular 
 mixtures of species of bacteria which have been 
 discovered to produce the desired effects. 
 
 CHAPTER IV. 
 
 BACTERIA IN NATURAL PROCESSES. 
 
 AGRICULTURE. 
 
 THUS far, in considering the relations of bac- 
 teria to mankind, we have taken into account only 
 the arts and manufactures, and have found bac- 
 teria playing no unimportant part in many of the 
 industries of our modern civilized life. So im- 
 portant are they that there is no one who is not 
 directly affected by them. There is hardly a mo- 
 ment in our life when we are not using some of 
 the direct or indirect products of bacterial action. 
 We turn now, however, to the consideration of a 
 matter of even more fundamental importance ; 
 for when we come to study bacteria in Nature, 
 we find that there are certain natural processes 
 connected with the life of animals and plants that 
 are fundamentally based upon their powers. Liv- 
 ing Nature appears limitless, for life processes 
 have been going on in the world through count- 
 less centuries with seemingly unimpaired vigour. 
 At the very bottom we find this never-ending ex- 
 hibition of vital power dependent upon certain 
 activities of micro-organisms. So thoroughly is 
 this true that, as we shall find after a short con- 
 sideration, the continuance of life upon the surface
 
 BACTERIA IN NATURAL PROCESSES. 95 
 
 of the world would be impossible if bacterial 
 action were checked for any considerable length 
 of time. The life of the globe is, in short, de- 
 pendent upon these micro-organisms. 
 
 BACTERIA AS SCAVENGERS. 
 
 In the first place, we may notice the value of 
 these organisms simply as scavengers, keeping 
 the surface of the earth in the proper condition 
 for the growth of animals and plants. A large 
 tree in the forest dies and falls to the ground. 
 For a while the tree trunk lies there a massive 
 structure, but in the course of months a slow 
 change takes place in it. The bark becomes sof- 
 tened and falls from the wood. The wood also 
 becomes more or less softened; it is preyed upon 
 then by insect life ; its density decreases more 
 and more, until finally it crumbles into a soft, 
 brownish, powdery mass, and eventually the 
 whole sinks into the soil, is overgrown by mosses 
 and other vegetation, and the tree trunk has dis- 
 appeared from view. In the same way the body 
 of the dead animal undergoes the process of the 
 softening of its tissues by decay. The softer 
 parts of the body rapidly dissipate, and even the 
 bones themselves eventually are covered with the 
 soil and disintegrated, until in time they, too, dis- 
 appear from any visible existence. This whole 
 process is one of decay, and the result is that 
 the solid mass of the body of the tree or of the 
 animal has been decomposed. What has become 
 of it ? The answer holds the secret of Nature's 
 eternal freshness. Part of it has dissipated into 
 the air in the form of gases and water vapour ; 
 part of it has changed its composition and has
 
 96 THE STORY OF GERM LIFE. 
 
 become incorporated into the soil, the final result 
 being that the body of the plant or animal disap- 
 pears as such, and its substance is converted into 
 gaseous form, which is dissipated in the air or into 
 simple compounds which sink into the earth. 
 
 This whole process of decay of organic life is 
 one in which bacteria play the most important 
 part. In the case of the decomposition of the 
 woody matter of the tree trunk, the process is be- 
 gun by the agency of moulds, for this group of 
 organisms alone appears to be capable of attack- 
 ing such hard woody structure. The later part 
 of the decay, however, is largely carried on bv 
 bacterial life. In the decomposition of the ani- 
 mal tissues, bacteria alone are the agents. Thus 
 the process by which organic matter is dissipated 
 into the air or incorporated into the soil is one 
 which is primarily presided over by bacterial 
 life. 
 
 Viewing this matter in a purely mechanical 
 light, the importance of bacteria in thus acting as 
 scavengers can hardly be overestimated. If we 
 think for a moment of the condition of the world 
 were there no such decomposing agents to rid the 
 earth's surface of the dead bodies of animals and 
 plants, we shall see that long since the earth 
 would have been uninhabitable. If the dead 
 bodies of plants and animals of past ages simply 
 accumulated on the surface of the ground with- 
 out any forces to reduce them into simple com- 
 pounds for dissipation, by their very bulk they 
 would have long since completely covered the 
 surface of the earth so as to afford no possible 
 room for further growth of plants and animals. 
 In a purely mechanical way, then, bacteria as de- 
 composition agents are necessary to keep the sur-
 
 BACTERIA IN NATURAL PROCESSES. 97 
 
 face of the earth fresh and unencumbered so that 
 life can continue. 
 
 BACTERIA AS AGENTS IN NATURE'S FOOD 
 CYCLE. 
 
 But the matter by no means ends here. When 
 we come to think of it, it is a matter of consider- 
 able surprise that the surface of the earth has 
 been able to continue producing animals and 
 plants for the many millions of years during 
 which life has been in existence. Plants and ani- 
 mals both require food, animals depending wholly 
 upon plants therefor. Plants, however, equally 
 with animals, require food, and although they ob- 
 tain a considerable portion of their food from the 
 air, yet no inconsiderable part of it is obtained 
 from the soil. The question is forced upon us, 
 therefore, as to why the soil has not long since 
 become exhausted of food. How could the soil 
 continue to support plants year after year for 
 millions of years, and yet remain as fertile as 
 ever? 
 
 The explanation of this phenomenon is in the 
 simple fact that the processes of Nature are such 
 that the same food is used over and over again, 
 first by the plant, then by the animal, and then 
 again by the plant, and there is no necessity for 
 any end of the process so long as the sun fur- 
 nishes energy to keep the circulation continuous. 
 One phase of this transference of food from 
 animal to plant and from plant to animal is 
 familiar to nearly every one. It is a well-known 
 fact that animals in their respiration consume 
 oxygen, but exhale it again in combination with 
 carbon as carbonic dioxide. On the other hand,
 
 98 THE STORY OF GERM LIFE. 
 
 plants in their life consume the carbonic dioxide 
 and exhale the oxygen again as free oxygen. 
 Thus each of these kingdoms makes use of the 
 excreted product of the other, and this process 
 can go on indefinitely, the animals furnishing our 
 atmosphere with plenty of carbonic acid for plant 
 life, and the plants excreting into the atmosphere 
 at the same time an abundant sufficiency of oxy- 
 gen for animal life. The oxygen thus passes in 
 an endless round from animal to plant and from 
 plant to animal. 
 
 A similar cycle is true of all the other foods 
 of animal and plant life, though in regard to the 
 others the operation is more complex and more 
 members are required to complete the chain. 
 The transference of matter through a series of 
 changes by which it is brought from a condition 
 in which it is proper food for plants back again 
 into a condition when it is once more a proper 
 food for plants, is one of the interesting dis- 
 coveries of modern science, and one in which, as 
 we shall see, bacteria play a most important part. 
 This food cycle is illustrated roughly by the 
 accompanying diagram ; but in order to under- 
 stand it, an explanation of the various steps in 
 this cycle is necessary. 
 
 It will be noticed that at the bottom of the 
 circle represented in Fig. 25, at A, are given 
 various ingredients which are found in the soil 
 and which form plant foods. Plant foods, as 
 may be seen there, are obtained partly from the 
 air as carbonic dioxide and water; but another 
 portion comes from the soil. Among the soil 
 ingredients the most prominent are nitrates, 
 which are the forms of nitrogen compounds 
 most easily made use of by plants as a source of
 
 BACTERIA IN NATURAL PROCESSES. 
 
 99 
 
 this important element. It should be stated also 
 that there are other compounds in the soil which 
 
 PRODUCTS OF ANIMAL LIFE 
 
 fRODUC 
 
 E'RCLE BACTERIA. 
 
 AND LEGUMES 
 
 SOIL - NITRATE 
 
 Flo. 25. Diagram illustrating Nature's food cycle. 
 Explained in the text. 
 
 furnish plants with part of their food com- 
 pounds containing potassium, phosphorus, and 
 some other elements. For simplicity's sake, 
 however, these will be left out of consideration. 
 Beginning at the bottom of the cycle (Fig. 25 A), 
 plant life seizes the gases from the air and these 
 foods from the soil, and by means of the energy 
 furnished it by the sun's rays builds these simple 
 chemical compounds into more complex ones. 
 This gives us the second step, as shown in Fig. 
 25 B, the products of plant life. These products
 
 100 THE STORY OF GERM LIFE. 
 
 of plant life consist of such materials as sugar, 
 starches, fats, and proteids, all of which have 
 been manufactured by the plant from the ingre- 
 dients furnished it from the soil and air, and 
 through the agency of the sun's rays. These 
 products of plant life now form foods for the 
 animal kingdom. Starches, fats, and proteids are 
 animal foods, and upon such complex bodies 
 alone can the animal kingdom be fed. Animal 
 life, standing high up in the circle, is not capable 
 of extracting its nutriment from the soil, but must 
 take the more complex foods which have been 
 manufactured by plant life. These complex 
 foods enter now into the animal and take their 
 place in the animal body. By the animal activi- 
 ties, some of the foods are at once decomposed 
 into carbonic acid and water, which, being dis- 
 sipated into the air, are brought back at once 
 into the condition in which they can serve again 
 as plant food. This part of the food is thus 
 brought back again to the bottom of the circle 
 (Fig. 25, dotted lines). But while it is true that 
 animals do thus reduce some of their foods to 
 the simple condition of carbonic acid and water, 
 this is not true of most of the foods which con- 
 tain nitrogen. The nitrogenous foods are as 
 necessary for the life as the carbon foods, and 
 animals do not reduce their nitrogenous foods 
 to the condition in which plants can prey upon 
 them. While plants furnish them with nitroge- 
 nous food, they can not give it back to the plants. 
 Part of the nitrogenous foods animals build into 
 new albumins (Fig. 25 C); but a part of them they 
 reduce at once into a somewhat simpler condition 
 known as urea. Urea is the form in which the 
 nitrogen is commonly excreted from the animal
 
 BACTERIA IN NATURAL PROCESSES. IOI 
 
 body. But urea is not a plant food; for ordinary 
 plants are entirely unable to make use of it. 
 Part of the nitrogen eaten by the animal is stored 
 up in its body, and thus the body of the animal, 
 after it has died, contains these nitrogen com- 
 pounds of high complexity. But plants are not 
 able to use these compounds. A plant can not be 
 fed upon muscle tissue, nor upon fats, nor bones, 
 for these are compounds so complex that the sim- 
 ple plant is unable to use them at all. So far, 
 then, in the food cycle the compounds taken from 
 the soil have been built up into compounds of 
 greater and greater complexity ; they have reached 
 the top of this circle, and no part of them, except 
 part of the carbon and oxygen, has become re- 
 duced again to plant food. In order that this 
 material should again become capable of enter- 
 ing into the life of plants so as to go over the 
 circle again, it is necessary for it to be once 
 more reduced from its highly complex condition 
 into a simpler one. 
 
 Now come into play these decomposition 
 agencies which we have been studying under the 
 head of scavengers. It will be noticed that the 
 next step in the food cycle is taken by the de- 
 composition bacteria. These organisms, exist- 
 ing, as we have already seen, in the air, in the 
 soil, in the water, and always ready to seize hold 
 of any organic substance that may furnish them 
 with food, feed upon the products of animal life, 
 whether they are such products as muscle tissue, 
 or fat, or sugar, or whether they are the excreted 
 products of animal life, such as urea, and produce 
 therein the chemical decomposition changes al- 
 ready noticed. As a result of this chemical 
 decomposition, the complex bodies are broken
 
 102 THE STORY OF GERM LIFE. 
 
 into simpler and simpler compounds, and the 
 final result is a very thorough destruction of the 
 animal body or the material excreted by animal 
 life, and its reduction into forms simple enough 
 for plants to use again as foods. Thus the bac- 
 teria come in as a necessary link to connect the 
 animal body, or the excretion from the animal 
 body, with the soil again, and therefore with that 
 part of the circle in which the material can once 
 more serve as plant food. 
 
 But in the decomposition that thus occurs 
 through the agency of the putrefactive bacteria 
 it very commonly happens that some of the food 
 material is broken down into compounds too sim- 
 ple for use as plant food. As will be seen by a 
 glance at the diagram (Fig. 25 D), a portion of the 
 cleavage products resulting from the destruction 
 of these animal foods takes the form of carbonic- 
 acid gas and water. These ingredients are at 
 once in condition for plant life, as shown by the 
 dotted lines. They pass off into the air, and the 
 green leaves of vegetation everywhere again 
 seize them, assimilate them, and use them as 
 food. Thus it is that the carbon and the oxygen 
 have completed the cycle, and have come back 
 again to the position in the circle where they 
 started. In regard to the nitrogen portion of the 
 food, however, it very commonly happens that the 
 products which arise as the result of the decom- 
 position processes are not yet in proper condition 
 for plant food. They are reduced into a condition 
 actually too simple for the use of plants. As a 
 result of these putrefactive changes, the nitrogen 
 products of animal life are broken frequently 
 into compounds as simple as ammonia (NH 3 ), or 
 into compounds which the chemists speak of as
 
 BACTERIA IN NATURAL PROCESSES. 103 
 
 nitrites (Fig. 25 at D). Now these compounds are 
 not ordinarily within the reach of plant life. The 
 luxuriant vegetation of the globe extracts its ni- 
 trogen from the soil in a form more complex than 
 either of the compounds here mentioned ; for, as 
 we have seen, it is nitrates chiefly that furnish 
 plants with their nitrogen food factor. But ni- 
 trates contain considerable oxygen. Ammonia, 
 which is one of the products of putrefactive de- 
 composition, contains no oxygen, and nitrites, an- 
 other factor, contains less oxygen than nitrates. 
 These bodies are thus too simple for plants to 
 make use of as a source of nitrogen. The chem- 
 ical destruction of the food material which results 
 from the action of the putrefactive bacteria is too 
 thorough, and the nitrogen foods are not yet in 
 condition to be used by plants. 
 
 Now comes in the agency of still another class 
 of micro-organisms, the existence of which has 
 been demonstrated to us during the last few years. 
 In the soil everywhere, espe- 
 cially in fertile soil, is a class 
 of bacteria which has received 
 the name of nitrifying bacteria 
 (Fig. 26). These organisms 
 grow in the soil and feed upon 
 the soil ingredients. In the FIG. 26. Soil bacteria 
 course of their life they have Trification? " 
 somewhat the same action upon 
 the simple nitrogen cleavage products just men- 
 tioned as we have already noticed the vinegar- 
 producing species have upon alcohol, viz., the 
 bringing about a union with oxygen. There are 
 apparently several different kinds of nitrifying 
 bacteria with different powers. Some of them 
 cause an oxidation of the nitrogen products by
 
 104 THE STORY OF GERM LIFE. 
 
 means of which the ammonia is united with oxy. 
 gen and built up into a series of products finally 
 resulting in nitrates (Fig. 26). By the action of 
 other species still higher nitrogen compounds, in- 
 cluding the nitrites, are further oxidized and built 
 up into the form of nitrates. Thus these nitrify- 
 ing organisms form the last link in the chain that 
 binds the animal kingdom to the vegetable king- 
 dom (Fig. 25 at 4). For after the nitrifying or- 
 ganisms have oxidized nitrogen cleavage products, 
 the results of the oxidation in the form of nitrates 
 or nitric acid are left in the soil, and may now be 
 seized upon by the roots of plants, and begin once 
 more their journey around the food cycle. In this 
 way it will be seen that while plants, by building 
 up compounds, form the connecting link between 
 the soil and animal life, bacteria in the other half 
 of the cycle, by reducing them again, give us the 
 connecting link between animal life and the soil. 
 The food cycle would be as incomplete without 
 the agency of bacterial life as it would be with- 
 out the agency of plant life. 
 
 But even yet the food cycle is not complete. 
 Some of the processes of decomposition appear 
 to cause a portion of the nitrogen to fly out of 
 the circle at a tangent. In the process of de- 
 composition which is going on through the 
 agency of micro-organisms, a considerable part 
 of the nitrogen is dissipated into the air in the 
 form of free nitrogen. When a bit of meat de- 
 cays, part of the meat is, indeed, converted into 
 ammonia or other nitrogen compounds, but if the 
 putrefaction is allowed to go on, in the end a 
 considerable portion of it will be broken into 
 still simpler forms, and the nitrogen will finally be 
 dissipated into the air in the form of free nitro-
 
 BACTERIA IN NATURAL PROCESSES. 105 
 
 gen. This dissipation of free nitrogen into the 
 air is going on in the world wherever putrefaction 
 takes place. Wherever decomposition of nitrogen 
 products occurs some free nitrogen is eliminated. 
 Now, this part of the nitrogen has passed beyond 
 the reach of plants, for plants can not extract 
 free nitrogen from the air. In the diagram this is 
 represented as a portion of the material which, 
 through the agency of the decomposition bacte- 
 ria, has been thrown out of the cycle at a tan- 
 gent (Fig. 25 E). It will, of course, be plain 
 from this that the store of nitrogen food must be 
 constantly diminishing. The soil may have been 
 originally supplied with a given quantity of nitro- 
 gen compound, but if the decomposition products 
 are causing considerable quantities of this nitro- 
 gen to be dissipated in the air, it plainly follows 
 that the total amount of nitrogen food upon 
 which the animal and vegetable kingdoms can 
 depend is becoming constantly reduced by such 
 dissipation. 
 
 There are still other methods by which nitro- 
 gen is being lost from the food cycle. First, we 
 may notice that the ordinary processes of vegeta- 
 tion result in a gradual draining of the soil and 
 a throwing of its nitrogen into the ocean. The 
 body of any animal or any plant that chances to 
 fall into a brook or river is eventually carried to 
 the sea, and the products of its decomposition 
 pass into the ocean and are, of course, lost to the 
 soil. Now, while this gradual extraction of ni- 
 trogen from the soil by drainage is a slow one, it 
 is nevertheless a sure one. It is far more rapid 
 in these years of civilized life than in former 
 times, since the products of the soil are given to 
 the city, and then are thrown into its sewage.
 
 to6 THE STORY OF GERM LIFE. 
 
 Our cities, then, with our present system of dis- 
 posing of sewage, are draining from the soil the 
 nitrogen compounds and throwing them away. 
 
 In yet another direction must it be noticed 
 that our nitrogen compounds are being lost to 
 plant life viz., by the use of various nitrogen 
 compounds to form explosives. Gunpowder, ni- 
 tro-glycerine, dynamite, in fact, nearly all the ex- 
 plosives that are used the world over for all sorts 
 of purposes, are nitrogen compounds. When they 
 are exploded the nitrogen of the compound is 
 dissipated into the air in the form of gas, much 
 of it in the form of free nitrogen. The basis 
 from which explosive compounds are made con- 
 tains nitrogen in the form in which it can be used 
 by plants. Saltpetre, for example, is equally 
 good as a fertilizer and as a basis for gunpowder. 
 The products of the explosion are gases no 
 longer capable of use by plants, and thus every 
 explosion of nitrogen compounds aids in this 
 gradual dissipation of nitrogen products, taking 
 them from the store of plant foods and throwing 
 them away. 
 
 All of these agencies contribute to reduce the 
 amount of material circulating in the food cycle 
 of Nature, and thus seem to tend inevitably in 
 the end toward a termination of the processes of 
 life; for as soon as the soil becomes exhausted of 
 its nitrogen compounds, so soon will plant life 
 cease .from lack of nutrition, and the disappear- 
 ance of animal life will follow rapidly. It is this 
 loss of nitrogen in large measure that is forcing 
 our agriculturists to purchase fertilizers. The 
 last fifteen years have shown us, however, that 
 here again we may look upon our friends, the 
 bacteria, as agents for counteracting this dissi-
 
 BACTERIA IN NATURAL PROCESSES. 107 
 
 paring tendency in the general processes of Na- 
 ture. Bacterial life in at least two different ways 
 appears to have the function of reclaiming from 
 the atmosphere more or less of this dissipated 
 free nitrogen. 
 
 In the first place, it has been found in the 
 last few years that soil entirely free from all 
 common plants, but containing certain kinds of 
 bacteria, if allowed to stand in contact with the 
 air, will slowly but surely gain in the amount of 
 nitrogen compounds that it contains. These 
 nitrogen compounds are plainly manufactured by 
 the bacteria in the soil ; for unless the bacteria are 
 present they do not accumulate, and they do ac- 
 cumulate inevitably if the bacteria are present in 
 the proper quantity and the proper species. It 
 appears that, as a rule, this fixation of nitrogen 
 is not performed by any one species of micro- 
 organisms, but by two or three of them acting 
 together. Certain combinations of bacteria have 
 been found which, when inoculated in the soil, 
 will bring about this fixation of nitrogen, but no 
 one of the species is capable of producing this 
 result alone. We do not know to what extent 
 these organisms are distributed in the soil, nor 
 how widely this nitrogen fixation through bacte- 
 rial life is going on. It is only within a short 
 time that it has been demonstrated to exist, but 
 we must look upon bacteria in the soil as one of 
 the factors in reclaiming from the atmosphere the 
 dissipated free nitrogen. 
 
 The second method by which bacteria aid in 
 the reclaiming of this lost nitrogen is by a com- 
 bined action of certain species of bacteria and 
 some of the higher plants. Ordinary green 
 plants, as already noted, are unable to make use
 
 I08 THE STORY OF GERM LIFE. 
 
 of the free nitrogen of the atmosphere. It was 
 found, however, some fifteen years ago that some 
 species of plants, chiefly the great family of 
 legumes, which contains the pea plant, the bean, 
 the clover, etc., are able, when growing in soil 
 that is poor in nitrogen, to obtain nitrogen from 
 some source other than the soil in which they 
 grow. A pea plant in soil that contains no nitro- 
 gen products and watered with water that con- 
 tains no nitrogen, will, after sprouting and growing 
 for a length of time, be found to have accumu- 
 lated a considerable quantity of fixed nitrogen in 
 its tissues. The only source of this nitrogen has 
 been evidently from the air which bathes the 
 leaves of the plant or permeates the soil and 
 bathes its roots. This fact 
 was at first disputed, but sub- 
 sequently demonstrated to be 
 tru e, and was found later to 
 be associated with the com- 
 bined action of these legumes 
 and certain soil bacteria. 
 When a legume thus gains 
 FIG. 2 7 .-Soii bacteria nitrogen from the air, it de- 
 which produce tu- velops upon its roots little 
 bercies on the roots bunches known as root nod- 
 ules or root tubercles. The 
 nodules are sometimes the size of the head of a 
 pin, and sometimes much larger than this, occa- 
 sionally reaching the size of a large pea, or even 
 larger. Upon microscopic examination they 
 are found to be little nests of bacteria. In some 
 way the soil organisms (Fig. 27) make their way 
 into the roots of the sprouting plant, and find- 
 ing there congenial environment, develop in con- 
 siderable quantities and produce root tubercles
 
 BACTERIA IN NATURAL PROCESSES. 109 
 
 in the root. Now, by some entirely unknown 
 process, the legume and the bacteria growing to- 
 gether succeed in extracting the nitrogen from 
 the atmosphere which permeates the soil, and fix- 
 ing this nitrogen in the tubercles and the roots in 
 the form of nitrogen compounds. The result is 
 that, after a proper period of growth, the amount 
 of fixed nitrogen in the plant is found to have 
 very decidedly increased (Fig. 25 E.). 
 
 This, of course, furnishes a starting point for 
 the reclaiming of the lost atmospheric nitrogen. 
 The legume continues to live its usual life, per- 
 haps increasing the store of nitrogen in its roots 
 and stems and leaves during the whole of its 
 normal growth. Subsequently, after having fin- 
 ished its ordinary life, the plant will die, and then 
 the roots and stems and leaves, falling upon the 
 ground and becoming buried, will be seized upon 
 by the decomposition bacteria already men- 
 tioned. The nitrogen which has thus become 
 fixed in their tissues will undergo the destructive 
 changes already described. This will result 
 eventually in the production of nitrates. Thus 
 some of the lost nitrogen is restored again to the 
 soil in the form of nitrates, and may now start 
 on its route once more around the cycle of food. 
 
 It will be seen, then, that the food cycle is a 
 complete one. Beginning with the mineral in- 
 gredients in the soil, the food matter may start 
 on its circulation from the soil to the plant, from 
 the plant to the animal, from the animal to the 
 bacterium, and from the bacterium through a 
 series of other bacteria back again to the soil in 
 the condition in which it started. If, perchance, 
 in this progress around the circle some of the 
 nitrogen is thrown off at a tangent, this, too,
 
 110 THE STORY OF GERM LIFE. 
 
 is brought back again to the circle through 
 the agency of bacterial life. And so the food 
 material of animals and plants continues in this 
 never-ceasing circulation. It is the sunlight that 
 furnishes the energy for the motion. It is the 
 sunlight that forces the food around the circle 
 and keeps up the endless change; and so long as 
 the sun continues to shine upon the earth there 
 seems to be no reason why the process should 
 ever cease. It is this repeated circulation that 
 has made the continuation of life possible for the 
 millions and millions of years of the earth's his- 
 tory. It is this continued circulation that makes 
 life possible still, and it is only this fact that the 
 food is thus capable of ever circulating from ani- 
 mal to plant and from plant to animal that makes 
 it possible for the living world to continue its 
 existence. But, as we have seen, one half of this 
 great circle of food change is dependent upon 
 bacterial life. Without the bacterial life the ani- 
 mal body and the animal excretion could never 
 be brought back again within the reach of the 
 plant; and thus, were it not for the action of 
 these micro-organisms the food cycle would be 
 incomplete and life could not continue indefi- 
 nitely upon the surface of the earth. At the 
 very foundation, the continuation of the present 
 condition of Nature and the existence of life 
 during the past history of the world has been 
 fundamentally based upon the ubiquitous pres- 
 ence of bacteria and upon their continual action 
 in connection with both destructive and con- 
 structive processes.
 
 BACTERIA IN NATURAL PROCESSES. Ill 
 RELATION OF BACTERIA TO AGRICULTURE. 
 
 We have already noticed that bacteria play 
 an important part in some of the agricultural in- 
 dustries, particularly in the dairy. From the 
 consideration of the matters just discussed, it is 
 manifest that these organisms must have an even 
 more intimate relation to the farmer's occupation. 
 At the foundation, farming consists in the culti- 
 vation of plants and animals, and we have al- 
 ready seen how essential are the bacteria in the 
 continuance of animal and plant life. But aside 
 from these theoretical considerations, a little 
 study shows that in a very practical manner the 
 farmer is ever making use of bacteria, as a rule, 
 quite unconsciously, but none the less positively. 
 
 SPROUTING OF SEEDS. 
 
 Even in the sprouting of seeds after they are 
 sown in the soil bacterial life has its influence. 
 When seeds are placed in moist soil they germi- 
 nate under the influence of heat. The rich albu- 
 minous material in the seeds furnishes excellent 
 food, and inasmuch as bacteria abound in the 
 soil, it is inevitable that they should grow in and 
 feed upon the seed. If the moisture is excessive 
 and the heat considerable, they very frequently 
 grow so rapidly in the seed as to destroy its life 
 as a seedling. The seed rots in the ground as a 
 result. This does not commonly occur, however, 
 in ordinary soil. But even here bacteria do grow 
 in the seed, though not so abundantly as to pro- 
 duce any injury. Indeed, it has been claimed 
 that their presence in the seed in small quantities 
 is a necessity for the proper sprouting of the
 
 112 THE STORY OF GERM LIFE. 
 
 seed. It has been claimed that their growth tends 
 to soften the food material in the seed, so that 
 the young seedling can more readily absorb it for 
 its own food, and that without such a softening 
 the seed remains too hard for the plant to use. 
 This may well be doubted, however, for seeds 
 can apparently sprout well enough without the 
 aid of bacteria. But, nevertheless, bacteria do 
 grow in the seed during its germination, and thus 
 do aid the plant in the softening of the food ma- 
 terial. We can not regard them as essential to 
 seed germination. It may well be claimed that 
 they ordinarily play at least an incidental part in 
 this fundamental life process, although it is un- 
 certain whether the growth of seedlings is to any 
 considerable extent aided thereby. 
 
 THE SILO. 
 
 In the management of a silo the farmer has 
 undoubtedly another great bacteriological prob- 
 lem. In the attempt to preserve his summer- 
 grown food for the winter use of his animals, 
 he is hindered by the activity of common bac- 
 teria. If the food is kept moist, it is sure to 
 undergo decomposition and be ruined in a short 
 time as animal food. The farmer finds it neces- 
 sary, therefore, to dry some kinds of foods, like 
 hay. While he can thus preserve some foods, 
 others can not be so treated. Much of the rank 
 growth of the farm, like cornstalks, is good food 
 while it is fresh, but is of little value when dried. 
 The farmer has from experience and observation 
 discovered a method of managing bacterial 
 growth which enables him to avoid their ordinary 
 evil effects. This is by the use of the silo. The
 
 BACTERIA IN NATURAL PROCESSES. 113 
 
 silo is a large, heavily built box, which is open 
 only at the top. In the silo the green food is 
 packed tightly, and when full all access of air is 
 excluded, except at its surface. Under these 
 conditions the food remains moist, but neverthe- 
 less does not undergo its ordinary fermentations 
 and putrefactions, and may be preserved for 
 months without being ruined. The food in such 
 a silo may be taken out months after it is packed, 
 and will still be found to be in good condition foi 
 food. It is true that it has changed its charac- 
 ter somewhat, but it is not decayed, and is eagerly 
 eaten by cattle. 
 
 We are yet very ignorant of the nature of the 
 changes which occur in the food while in the silo. 
 The food is not preserved from fermentation. 
 When the silo is packed slowly, a very decided 
 fermentation occurs by which the mass is raised 
 to a high temperature (140 F. to 160 F.). 
 This heating is produced by certain species of 
 bacteria which grow readily even at this high 
 temperature. The fermentation uses up the air 
 in the silo to a certain extent and produces a 
 settling of the material which still further ex- 
 cludes air. The first fermentation soon ceases, 
 and afterward only slow changes occur. Certain 
 acid-producing bacteria after a little begin to 
 grow slowly, and in time the silage is rendered 
 somewhat sour by the production of acetic acid. 
 But the exclusion of air, the close packing, and 
 the small amount of moisture appear to prevent 
 the growth of the common putrefactive bacteria, 
 and the silage remains good for a long time. In 
 other methods of filling the silo, the food is very 
 quickly packed and densely crowded together so 
 as to exclude as much air as possible from the
 
 114 THE STORY OF GERM LIFE. 
 
 beginning. Under these conditions the lack of 
 moisture and air prevents fermentative action 
 very largely. Only certain acid-producing organ- 
 isms grow, and these very slowly. The essential 
 result in either case is that the common putrefac- 
 tive bacteria are prevented from growing, proba- 
 bly by lack of sufficient oxygen and moisture, 
 and thus the decay is prevented. The closely 
 packed food offers just the same unfavourable 
 condition for the growth of common putrefactive 
 bacteria that we have already seen offered by the 
 hard-pressed cheese, and the bacteria growth is 
 in the same way held in check. Our knowledge 
 of the matter is as yet very slight, but we do 
 know enough to understand that the successful 
 management of a silo is dependent upon the 
 manipulation of bacteria. 
 
 THE FERTILITY OF THE SOIL. 
 
 The farmer's sole duty is to extract food 
 from the soil. This he does either directly by 
 raising crops, or indirectly by raising animals 
 which feed upon the products of the soil. In 
 either case the fertility of the soil is the funda- 
 mental factor in his success. This fertility is a 
 gift to him from the bacteria. 
 
 Even in the first formation of soil he is in a 
 measure dependent upon bacteria. Soil, as is well 
 known, is produced in large part by the crum- 
 bling of the rocks into powder. This crumbling 
 we generally call weathering, and regard it as due 
 to the effect of moisture and -cold upon the rocks, 
 together with the oxidizing action of the air. 
 Doubtless this is true, and the weathering action 
 is largely a physical and chemical one. Never-
 
 BACTERIA IN NATURAL PROCESSES. 115 
 
 theless, in this fundamental process of rock disin- 
 tegration bacterial action plays a part, though 
 perhaps a small one. Some species of bacteria, 
 as we have seen, can live upon very simple foods, 
 finding in free nitrogen and carbonates sufficient- 
 ly highly complex material for their life. These 
 organisms appear to grow on the bare surface of 
 rocks, assimilating nitrogen from the air, and car- 
 bon from some widely diffused carbonates or from 
 the COa in the air. Their secreted products of 
 an acid nature help to soften the rocks, and thus 
 aid in performing the first step in weathering. 
 
 The soil is not, however, all made up of dis- 
 integrated rocks. It contains, besides, various 
 ingredients which combine to make it fertile. 
 Among these are various sulphates which form 
 important parts of plant foods. These sulphates 
 appear to be formed, in part, at least, by bacterial 
 agency. The decomposition of proteids gives 
 rise, among other things, to hydrogen sulphide 
 (HS). This gas, which is of common occurrence 
 in the atmosphere, is oxidized by bacterial growth 
 into sulphuric acid, and this is the basis of part 
 of the soil sulphates. The deposition of iron 
 phosphates and iron silicates is probably also in 
 a measure aided by bacterial action. All of these 
 processes are factors in the formation of soil. 
 Beyond much question the rock disintegration 
 which occurs everywhere in Nature is chiefly the 
 result of physical and chemical changes, but there 
 is reason for believing that the physical and chem- 
 ical processes are, to a slight extent at least, as- 
 sisted by bacterial life. 
 
 A more important factor of soil fertility is its 
 nitrogen content, without which it is complete- 
 ly barren. The origin of these nitrogen ingre-
 
 Il6 THE STORY OF GERM LIFE. 
 
 dients has been more or less of a puzzle. Fertile 
 soil everywhere contains nitrates and other nitro- 
 gen compounds, and in certain parts of the world 
 there are large accumulations of these compounds, 
 like the nitrate beds of Chili. That they have 
 come ultimately from the free atmospheric nitro- 
 gen seems certain, and various attempts have been 
 made to explain a method of this nitrogen fixa- 
 tion. It has been suggested that electrical dis- 
 charges in the air may form nitric acid, which 
 would readily then unite with soil ingredients to 
 form nitrates. There is little reason, however, 
 for believing this to be a very important factor. 
 But in the soil bacteria we find undoubtedly an 
 efficient agency in this nitrogen fixation. As al- 
 ready seen, the bacteria are able to seize the free 
 atmospheric nitrogen, converting it into nitrites 
 and nitrates. We have also learned that they 
 can act in connection with legumes and some 
 other plants, enabling them to fix atmospheric ni- 
 trogen and store it in their roots. By these two 
 means the nitrogen ingredient in the soil is pre- 
 vented from becoming exhausted by the processes 
 of dissipation constantly going on. Further, by 
 some such agency must we imagine the original 
 nitrogen soil ingredient to have been derived. 
 Such an organic agency is the only one yet dis- 
 cerned which appears to have been efficient in 
 furnishing virgin soil with its nitrates, and we 
 must therefore look upon bacteria as essential to 
 the original fertility of the soil. 
 
 But in another direction still does the farmer 
 depend directly upon bacteria. The most impor- 
 tant factor in the fertility of the soil is the part 
 of it called humus. This humus is very complex, 
 and never alike in different soils. It contains ni-
 
 BACTERIA IN NATURAL PROCESSES. 117 
 
 trogen compounds in abundance, together with 
 sulphates, phosphates, sugar, and many other sub- 
 stances. It is this which makes the garden soil 
 different from sand, or the rich soil different from 
 the sterile soil. If the soil is cultivated year after 
 year, its food ingredients are slowly but surely 
 exhausted. Something is taken from the humus 
 each year, and unless this be replaced the soil 
 ceases to be able to support life. To keep up a 
 constant yield from the soil the farmer under- 
 stands that he must apply fertilizers more or less 
 constantly. 
 
 This application of fertilizers is simply feed- 
 ing the crops. Some of these fertilizers the farm- 
 er purchases, and knows little or nothing as to 
 their origin. The most common method of feed- 
 ing the crops is, however, by the use of ordinary 
 barnyard manure. The reason why this material 
 contains plant food we can understand, since it 
 is made of the undigested part of food, together 
 with all the urea and other excretions of animals, 
 and contains, therefore, besides various minerals, 
 all of the nitrogenous waste of animal life. These 
 secretions are not at first fit for plant food. The 
 farmer has learned by experience that such excre- 
 tions, before they are of any use on his fields, 
 must undergo a process of slow change, which 
 is sometimes called ripening. Fresh manure is 
 sometimes used on the fields, but it is only made 
 use of by the plants after the ripening process 
 has occurred. Fresh animal excretions are of 
 little or no value as a fertilizer. The farmer, 
 therefore, commonly allows it to remain in heaps 
 for some time, and it undergoes a slow change, 
 which gradually converts it into a condition in 
 which it can be used by plants. This ripening is
 
 Il8 THE STORY OF GERM LIFE. 
 
 readily explained by the facts already considered. 
 The fresh animal secretions consist of various 
 highly complex compounds of nitrogen, and the 
 ripening is a process of their decomposition. The 
 proteids are broken to pieces, and their nitrogen 
 elements reduced to the form of nitrates, leucin, 
 etc., or even to ammonia or free nitrogen. Fur- 
 ther, a second process occurs, the process of 
 oxidation of these nitrogen compounds already 
 noticed, and the ammonia and nitrites resulting 
 from the decomposition are built into nitrates. 
 In short, in this ripening manure the processes 
 noticed in the first part of this chapter are taking 
 place, by which the complex nitrogenous bodies 
 are first reduced and then oxidized to form plant 
 food. The ripening of manure is both an ana- 
 lytical and a synthetical process. By the analy- 
 sis, proteids and other bodies are broken into very 
 simple compounds, some of them, indeed, being 
 dissipated into the air, but other portions are re- 
 tained and then oxidized, and these latter become 
 the real fertilizing materials. Through the agency 
 of bacteria the compost heap thus becomes the 
 great source of plant food to the farmer. Into 
 this compost heap he throws garbage, straw, vege- 
 table and animal substances in general, or any 
 organic refuse which may be at hand. The vari- 
 ous bacteria seize it all, and cause the decomposi- 
 tion which converts it into plant food again. The 
 rotting of the compost heap is thus a gigantic 
 cultivation of bacteria. 
 
 This knowledge of the ripening process is fur- 
 ther teaching the farmer how to prevent waste. 
 In the ordinary decomposition of the compost 
 heap not an inconsiderable portion of the nitro- 
 gen is lost in the air by dissipation as ammonia
 
 BACTERIA IN NATURAL PROCESSES. 119 
 
 or free nitrogen. Even his nitrates may be thus 
 lost by bacterial action. This portion is lost to 
 the farmer completely, and he can only hope to 
 replace it either by purchasing nitrates in the 
 form of commercial fertilizers, or by reclaiming it 
 from the air by the use of the bacterial agencies 
 already noticed. With the knowledge now at his 
 command he is learning to prevent this waste. 
 In the decomposition one large factor of loss is 
 the ammonia, which, being a gas, is readily dis- 
 sipated into the air. Knowing this common re- 
 sult of bacterial action, the scientist has told the 
 farmer that, by adding certain common chemic- 
 als to his decomposing manure heap, chemicals 
 which will readily unite with ammonia, he may 
 retain most of the nitrogen in this heap in the 
 form of ammonia salts, which, once formed, no 
 longer show a tendency to dissipate into the air. 
 Ordinary gypsum, or superphosphates, or plaster 
 will readily unite with ammonia, and these added 
 to the manure heap largely counteract the tend- 
 ency of the nitrogen to waste, thus enabling the 
 farmer to put back into his soil most of the nitro- 
 gen which was extracted from it by his crops 
 and then used by his stock. His vegetable crops 
 raise the nitrates into proteids. His animals feed 
 upon the proteids, and perform his work or fur- 
 nish him with milk. Then his bacteria stock 
 take the excreted or refuse nitrogen, and in his 
 manure heap turn it back again into nitrates 
 ready to begin the circle once more. This might 
 go on almost indefinitely wpre it not for two 
 facts : the farmer sends nitrogenous material off 
 his farm in the milk or grains or other nitro- 
 genous products which he sells, and the de- 
 composition processes, as we have seen, dissi-
 
 120 THE STORY OF GERM LIFE. 
 
 pate some of the nitrogen into the air as free ni- 
 trogen. 
 
 To meet this emergency and loss the farmer 
 has another method of enriching the soil, again 
 depending upon bacteria. This is the so-called 
 green manuring. Here certain plants which seize 
 nitrogen from the air are cultivated upon the field 
 to be fertilized, and, instead of harvesting a 
 crop, it is ploughed into the soil. Or perhaps 
 the tops may be harvested, the rest being 
 ploughed into the soil. The vegetable material 
 thus ploughed in lies over a season and enriches 
 the soil. Here the bacteria of the soil come into 
 play in several directions. First, if the crop 
 sowed be a legume, the soil bacteria assist it to 
 seize the nitrogen from the air. The only plants 
 which are of use in this green manuring are those 
 which can, through the agency of bacteria, obtain 
 nitrogen from the air and store it in their roots. 
 Second, after the crop is ploughed into the soil 
 various decomposing bacteria seize upon it, pulling 
 the compounds to pieces. The carbon is largely 
 dissipated into the air as carbonic dioxide, where 
 the next generation of plants can get hold of it. 
 The minerals and the nitrogen remain in the soil. 
 The nitrogenous portions go through the same 
 series of decomposition and synthetical changes 
 already described, and thus eventually the nitro- 
 gen seized from the air by the combined action 
 of the legumes and the bacteria is converted into 
 nitrates, and will serve for food for the next set 
 of plants grown on the same soil. Here is thus a 
 practical method of using the nitrogen assimila- 
 tion powers of bacteria, and reclaiming nitrogen 
 from the air to replace that which has been lost. 
 
 Thus it is that the farmer's nitrogen problem
 
 BACTERIA IN NATURAL PROCESSES. 121 
 
 of the fertile soil appears to resolve itself into a 
 proper handling of bacteria. These organisms 
 have stocked his soil in the first place. They 
 convert all of his compost heap wastes into simple 
 bodies, some of which are changed into plant 
 foods, while others are at the same time lost. 
 Lastly, they may be made to reclaim this lost 
 nitrogen, and the farmer, so soon as he has 
 requisite knowledge of these facts, will be able 
 to keep within his control the supply of this im- 
 portant element. The continued fertility of the 
 soil is thus a gift from the bacteria. 
 
 BACTERIA AS SOURCES OF TROUBLE TO THE 
 FARMER. 
 
 While the topics already considered comprise 
 the most important factors in agricultural bacte- 
 riology, the farmer's relations to bacteria do 
 not end here. These organisms come incidentally 
 into his life in many ways. They are not always 
 his aids as they are in most of the instances thus 
 far cited. They produce disease in his cattle, as 
 will be noticed in the next chapter. Bacteria are 
 agents of decomposition, and they are just as 
 likely to decompose material which the farmer 
 wishes to preserve as they are to decompose ma- 
 terial which the farmer desires to undergo the 
 process of decay. They are as ready to attack 
 his fruits and vegetables as to ripen his cream. 
 The skin of fruits and vegetables is a moderately 
 good protection of the interior from the attack 
 of bacteria; but if the skin be broken in any 
 place, bacteria get in and cause decay, and to 
 prevent it the farmer uses a cold cellar. The 
 bacteria prevent the farmer from preserving
 
 122 THE STORY OF GERM LIFE. 
 
 meats for any length of time unless he checks 
 their growth in some way. They get into the 
 eggs of his fowls and ruin them. Their trouble- 
 some nature in the dairy in preventing the keep- 
 ing of milk has already been noticed. If he 
 plants his seeds in very moist, damp weather, 
 the soil bacteria cause too rapid a decomposition 
 of the seeds and they rot in the ground instead 
 of sprouting. They produce disagreeable odours, 
 and are the cause of most of the peculiar smells, 
 good and bad, around the barn. They attack 
 the organic matter which gets into his well or 
 brook or pond, decomposing it, filling the water 
 with disagreeable and perhaps poisonous products 
 which render it unfit to drink. They not only aid 
 in the decay of the fallen tree in his forests, but 
 in the same way attack the timber which he 
 wishes to preserve, especially if it is kept in a 
 moist condition. Thus they contribute largely 
 to the gradual destruction of wooden structures. 
 It is therefore the presence of these organisms 
 which forces him to dry his hay, to smoke his 
 hams, to corn his beef, to keep his fruits and 
 vegetables cool and prevent skin bruises, to ice 
 his dairy, to protect his timber from rain, to use 
 stone instead of wooden foundations for build- 
 ings, etc. In general, when the farmer desires 
 to get rid of any organic refuse, he depends upon 
 bacteria, for they are his sole agents (aside from 
 fire) for the final destruction of organic matter. 
 When he wishes to convert waste organic refuse 
 into fertilizing material, he uses the bacteria of 
 his compost heap. On the other hand, whenever 
 he desires to preserve organic material, the 
 bacteria are the enemies against which he must 
 carefully guard.
 
 BACTERIA IN NATURAL PROCESSES. 123 
 
 Thus the farmer's life from year's end to year's 
 end is in most intimate association with bacteria. 
 Upon them he depends to insure the continued 
 fertility of his soil and the constant continued 
 production of good crops. Upon them he de- 
 pends to turn into plant food all the organic ref- 
 use from his house or from his barn. Upon 
 them he depends to replenish his stock of nitrogen. 
 It is these organisms which furnish his dairy with 
 its butter flavours and with the taste of its cheese. 
 But, on the other hand, against them he must be 
 constantly alert. All his food products must be 
 protected from their ravages. A successful farm- 
 er's life, then, largely resolves itself into a skilful 
 management of bacterial activity. To aid them 
 in destroying or decomposing everything which he 
 does not desire to preserve, and to prevent their 
 destroying the organic material which he wishes to 
 keep for future use, is the object of a considerable 
 portion of farm labour ; and the most successful 
 farmer to-day, and we believe the most successful 
 farmer of the future, is the one who most intelli- 
 gently and skilfully manipulates these gigantic 
 forces furnished him by the growth of his micro- 
 scopical allies. 
 
 RELATION OF BACTERIA TO COAL. 
 
 Another one of Nature's processes in which 
 bacteria have played an important part is in the 
 formation of coal. It is unnecessary to emphasize 
 the importance of coal in modern civilization. 
 Aside from its use as fuel, upon which civilization 
 is dependent, coal is a source of an endless variety 
 of valuable products. It is the source of our 
 illuminating gas, and ammonia is one of the prod-
 
 124 THE STORY OF GERM LIFE. 
 
 ucts of the gas manufacture. From the coal 
 also comes coal tar, the material from which such 
 a long series of valuable materials, as aniline 
 colours, carbolic acid, etc., is derived. The list of 
 products which we owe to coal is very long, and 
 the value of this material is hardly to be over- 
 rated. In the preparation of these ingredients 
 from coal bacteria do not play any part. Most 
 of them are derived by means of distillation. But 
 when asked for the agents which have given us 
 the coal of the coal beds, we shall find that here, 
 too, we owe a great debt to bacteria. 
 
 Coal, as is well known, has come from the ac- 
 cumulation of the luxuriant vegetable growth of 
 the past geological ages. It has therefore been 
 directly furnished us by the vegetation of the 
 green plants of the past, and, in general, it repre- 
 sents so much carbonic dioxide which these 
 plants have extracted from the atmosphere. But 
 while the green plants have been the active 
 agents in producing this assimilation, bacteria 
 have played an important part in coal manufac- 
 ture in two different directions. The first ap- 
 pears to be in furnishing these plants with 
 nitrogen. Without a store of fixed nitrogen in 
 the soil these carboniferous plants could not have 
 grown. This matter has already been considered. 
 We have no very absolute knowledge as to the 
 agency of bacteria in furnishing nitrogen for this 
 vegetation in past ages, but there is every reason 
 to believe that in the past, as in the present, the 
 chief source of organic nitrogen has been from 
 the atmosphere and derived from the atmos- 
 phere through the agency of bacteria. In the 
 absence of any other known factor we may be 
 pretty safe in the assumption that bacteria played
 
 BACTERIA IN NATURAL PROCESSES. 125 
 
 an important part in this nitrogen fixation, and 
 that bacteria must therefore be regarded as the 
 agents which have furnished us the nitrogen 
 stored in the coal. 
 
 But in a later stage of coal formation bacteria 
 have contributed more directly to the formation of 
 coal. Coal is not simply accumulated vegetation. 
 The coal of our coal beds is very different in its 
 chemical composition from the wood of the trees. 
 It contains a much higher percentage of carbon 
 and a lower percentage of hydrogen and oxygen 
 than ordinary vegetable substances. The conver- 
 sion of the vegetation of the carboniferous ages 
 into coal was accompanied by a gradual loss of 
 hydrogen and a consequent increase in the per- 
 centage of carbon. It is this change that has 
 added to the density of the substance and makes 
 the greater value of coal as fuel. There is little 
 doubt now as to the method by which this woody 
 material of the past has been converted into coal. 
 The same process appears to be going on in a 
 similar manner to-day in the peat beds of various 
 northern countries. The fallen vegetation, trees, 
 trunks, branches, and leaves, accumulate in 
 masses, and, when the conditions of moisture and 
 temperature are right, begin to undergo a fer- 
 mentation. Ordinarily this action of bacteria, 
 as already noticed, produces an almost complete 
 though slow oxidation of the carbon, and results 
 in the total decay of the vegetable matter. But 
 if the vegetable mass be covered by water and 
 mud under proper conditions of moisture and tem- 
 perature, a different kind of fermentation arises 
 which does not produce such complete decay. 
 The covering of water prevents the access of 
 oxygen to the fermenting mass, an oxidation of
 
 126 THE STORY OF GERM LIFE. 
 
 the carbon is largely prevented, and the vegetable 
 matter slowly changes its character. Under the 
 influence of this slow fermentation, aided, proba- 
 bly by pressure, the mass becomes more and more 
 solid and condensed, its woody character becomes 
 less and less distinct, and there is a gradual loss 
 of the hydrogen and the oxygen. Doubtless 
 there is a loss of carbon also, for there is an evo- 
 lution of marsh gas which contains carbon. But 
 in this slow fermentation taking place under the 
 water in peat bogs and marshes the carbon loss 
 is relatively small ; the woody material does not 
 become completely oxidized, as it does in free 
 operations of decay. The loss of hydrogen and 
 oxygen from the mass is greater than that of 
 carbon, and the percentage of carbon therefore in- 
 creases. This is not the ordinary kind of fermen- 
 tation that goes on in vegetable accumulations. 
 It requires special conditions and possibly special 
 kinds of fermenting organisms. Peat is not 
 formed in all climates. In warm regions, or 
 where the woody matter is freely exposed to the 
 air, the fermentation of vegetable matter is more 
 complete, and it is entirely destroyed by oxida- 
 tion. It is only in colder regions and when cov- 
 ered with water that the destruction of the organic 
 matter stops short of decay. But such incom- 
 plete fermentation is still going on in many parts 
 of the world, and by its means vegetable ac- 
 cumulations are being converted into peat. 
 
 This formation of peat appears to be a first 
 step in the formation of denser coal. By a con- 
 tinuation of the same processes the mass becomes 
 still more dense and solid. As we pass from the 
 top to the bottom of such an accumulation of 
 peat, we find it becoming denser and denser, and
 
 BACTERIA IN NATURAL PROCESSES. 127 
 
 at the bottom it is commonly of a hard consist- 
 ence, brownish in colour, and with only slight 
 traces of the original woody structure. Such 
 material is called lignite. It contains a higher 
 percentage of carbon than peat, but a lower per- 
 centage than coal, and is plainly a step in coal for- 
 mation. But the process goes on, the hydrogen 
 and oxygen loss continuing until there is finally 
 produced true coal. 
 
 If this is the correct understanding of the for- 
 mation of coal, we see that we have plainly a pro- 
 cess in which bacterial life has had a large and 
 important share. We are, of course, densely 
 ignorant of the exact processes going on. We 
 know nothing positively as to the kind of micro- 
 organisms which produce this slow, peculiar fer- 
 mentation. As yet, the fermentation going on in 
 the formation of the peat has not been studied 
 by the bacteriologists, and we do not know from 
 direct experiment that it is a matter of bacterial 
 action. It has been commonly regarded as sim- 
 ply a slow chemical change, but its general simi- 
 larity to other fermentative processes is so great 
 that we can have little hesitation in attributing it 
 to micro-organisms, and doubtless to some forms 
 of plants allied to bacteria. There is no reason 
 for doubting that bacteria existed in the geologi- 
 cal ages with essentially the same powers as 
 they now possess, and to some forms of bacteria 
 which grow in the absence of oxygen can we 
 probably attribute the slow change which has 
 produced coal. Here, then, is another great 
 source of wealth in Nature for which we are de- 
 pendent upon bacteria. While, of course, water 
 and pressure were very essential factors in the 
 deposition of coal, it was a peculiar kind of fer-
 
 128 THE STORY OF GERM LIFE. 
 
 mentation occurring in the vegetation that 
 brought about the chemical changes in it which 
 resulted in its transformation into coal. The vege- 
 tation of the carboniferous age was dependent 
 upon the nitrogen fixed by the bacteria, and to 
 these organisms also do we owe the fact that this 
 vegetation was stored for us in the rocks. 
 
 CHAPTER V. 
 
 PARASITIC BACTERIA AND THEIR RELATION TO 
 DISEASE. 
 
 PERHAPS the most universally known fact in 
 regard to bacteria is that they are the cause of 
 disease. It is this fact that has made them ob- 
 jects of such wide interest. This is the side of 
 the subject that first attracted attention, has been 
 most studied, and in regard to which there has 
 been the greatest accumulation of evidence. So 
 persistently has the relation of bacteria to disease 
 been discussed and emphasized that the majority 
 of readers are hardly able to disassociate the two. 
 To most people the very word bacteria is almost 
 equivalent to disease, and the thought of swallow- 
 ing microbes in drinking water or milk is decid- 
 edly repugnant and alarming. In the public mind 
 it is only necessary to demonstrate that an article 
 holds bacteria to throw it under condemnation. 
 
 We have already seen that bacteria are to be 
 regarded as agents for good, and that from their 
 fundamental relation to plant life they must be 
 looked upon as our friends rather than as our 
 enemies. It is true that there is another side to
 
 PARASITIC BACTERIA. 129 
 
 the story which relates to the parasitic species. 
 These parasitic forms may do us direct or indi- 
 rect injury. But the species of bacteria which are 
 capable of doing us any injury, \.\\t pathogenic bac- 
 teria, are really very few compared to the great 
 host of species which are harmless. A small 
 number of species, perhaps a score or two, are 
 pathogenic, while a much larger number, amount- 
 ing to hundreds and perhaps thousands of species, 
 are perfectly harmless. This latter class do no in- 
 jury even though swallowed by man in thousands. 
 They are not parasitic, and are unable to grow in 
 the body of man. Their presence is entirely con- 
 sistent with the most perfect health, and, indeed, 
 there are some reasons for believing that they 
 are sometimes directly beneficial to health. It is 
 entirely unjust to condemn all bacteria because a 
 few chance to produce mischief. Bacteria in gen- 
 eral are agents for good rather than ill. 
 
 There are, however, some species which cause 
 mankind much trouble by interfering in one way 
 or another with the normal processes of life. 
 These pathogenic bacteria, or disease germs, do 
 not all act alike, but bring about injury to man in 
 a number of different ways. We may recognise 
 two different classes among them, which, how- 
 ever, we shall see are connected by intermediate 
 types. These two classes are, first, the patho- 
 genic bacteria, which are not strictly parasitic but 
 live free in Nature; and, second, those which live 
 as true parasites in the bodies of man or other ani- 
 mals. To understand the real relation of these 
 two classes, we must first notice the method by 
 which bacteria in general produce disease.
 
 130 THE STORY OF GERM LIFE. 
 
 METHOD BY WHICH BACTERIA PRODUCE 
 DISEASE. 
 
 Since it was first clearly recognised that cer- 
 tain species of bacteria have the power of pro- 
 ducing disease, the question as to how they do 
 so has ever been a prominent one. Even if they 
 do grow in the body, why should their presence 
 give rise to the symptoms characterizing dis- 
 ease ? Various answers to this question have 
 been given in the past. It has been suggested 
 that in their growth they consume the food of 
 the body and thus exhaust it ; that they produce 
 .an oxidation of the body tissues, or that they 
 produce a reduction of these tissues, or that 
 they mechanically interfere with the circulation. 
 None of these suggestions have proved of much 
 value. Another view was early advanced, and has 
 stood the test of time. This claim is that the 
 bacteria while growing in the body produce poi- 
 sons, and these poisons then have a direct action 
 on the body. We have already noticed that bac- 
 teria during their growth in any medium produce 
 a large number of biprodiicts of decomposition. 
 We noticed also that among these biproducts 
 there are some which have a poisonous nature ; 
 so poisonous are they that when inoculated into 
 the body of an animal they may produce poison 
 ing and death. We have only to suppose that the 
 pathogenic bacteria, when growing as parasites in 
 man, produce such poisons, and we have at once 
 an explanation of the method by which they give 
 rise to disease. 
 
 This explanation of germ disease is more than 
 simple theory. It has been in many cases clearly 
 demonstrated. It has been found that the bac-
 
 PARASITIC BACTERIA. 131 
 
 teria which cause diphtheria, tetanus, typhoid,, 
 tuberculosis, and many other diseases, produce, 
 even when growing in common culture media, 
 poisons which are of a very violent nature. These 
 poisons when inoculated into the bodies of ani- 
 mals give rise to much the same symptoms as 
 the bacteria do themselves when growing as para- 
 sites in the animals. The chief difference in the 
 results from inoculating an animal with the poison 
 and with the living bacteria is in the rapidity of 
 the action. When the poison is injected the poi- 
 soning symptoms are almost immediately seen ; but 
 when the living bacteria are inoculated the effect 
 is only seen after several days or longer, not, in 
 short, until the inoculated bacteria have had time 
 enough to grow in the body and produce the poi- 
 son in quantity. It has not by any means been 
 shown that all pathogenic germs produce their 
 effect in this way, but it has been proved to be 
 the real method in quite a number of cases, and 
 is extremely probable in others. While some 
 bacteria perhaps produce results by a different 
 method, we must recognise the production of poi- 
 sons as at all events the common direct cause of 
 the symptoms of disease. This explanation will 
 enable us more clearly to understand the relation 
 of different bacteria to disease. 
 
 PATHOGENIC GERMS WHICH ARE NOT STRICTLY 
 PARASITIC. 
 
 Recognising that bacteria may produce poi- 
 sons, we readily see that it is not always neces- 
 sary that they should be parasites in order to 
 produce trouble. In their ordinary growth in 
 Nature such bacteria will produce no trouble.
 
 132 THE STORY OF GERM LIFE. 
 
 The poisons will be produced in decaying mate- 
 rial but will seldom be taken into the human 
 body. These poisons, produced in the first 
 stages of putrefaction, are oxidized by further 
 stages of decomposition into harmless products. 
 But should it happen that some of these bacteria 
 obtained a chance to grow vigorously for a while 
 in organic products that are subsequently swal- 
 lowed as man's food, it is plain that evil results 
 might follow. If such food is swallowed by man 
 after the bacteria have produced their poisonous 
 bodies, it will tend to produce an immediate poi- 
 soning of his system. The effect may be sudden 
 and severe if considerable quantity of the poison- 
 ous material is swallowed, or slight but protracted 
 if small quantities are repeatedly consumed in 
 food. Such instances are not uncommon. Well- 
 known examples are cases of ice-cream poison- 
 ing, poisoning from eating cheese or from drink- 
 ing milk, or in not a few instances from eating 
 fish or meats within which bacteria have had 
 opportunity for growth. In all these cases the 
 poison is swallowed in quantity sufficient to give 
 rise quickly to severe symptoms, sometimes re- 
 sulting fatally, and at other times passing off as 
 soon as the body succeeds in throwing off the 
 poisons. In other cases still, however, the 
 amount of poison swallowed may be very slight, 
 too slight to produce much effect unless the same 
 be consumed repeatedly. All such trouble may 
 be attributed to fermented or partly decayed 
 food. It is difficult to distinguish such instances 
 from others produced in a slightly different way, 
 as follows : 
 
 It may happen that the bacteria which grow 
 in food products continue to grow in the food
 
 PARASITIC BACTERIA. 133 
 
 even after it is swallowed and has passed into 
 the stomach or intestines. This appears particu- 
 larly true of milk bacteria. Under these condi- 
 tions the bacteria are not in any proper sense 
 parasitic, since they are simply living in and 
 feeding upon the same food which they consume 
 outside the body, and are not feeding upon the 
 tissues of man. The poisons which they produce 
 will continue to be developed as long as the bac- 
 teria continue to grow, whether in a milk pail or 
 a human stomach. If now the poisons are ab- 
 sorbed by the body, they may produce a mild or 
 severe disease which will be more or less lasting, 
 continuing perhaps as long as the same food and 
 the same bacteria are supplied to the individual. 
 The most important disease of this class appears 
 to be the dreaded cholera infantum, so common 
 among infants who feed upon cow's milk in warm 
 weather. It is easy to understand the nature of 
 this disease when we remember the great number 
 of bacteria in milk, especially in hot weather, 
 and when we remember that the delicate organ- 
 ism of the infant will be thrown at once into 
 disorder by slight amounts of poison which would 
 have no appreciable effect upon the stronger 
 adult. We can easily understand, further, how 
 the disease readily yields to treatment if care 
 is taken to sterilize the milk given to the pa- 
 tient. 
 
 We do not know to-day the extent of the 
 troubles which are produced by bacteria of this 
 sort. They will, of course, be chiefly connected 
 with our food products, and commonly, though 
 not always, will affect the digestive functions. It 
 is probable that many of the cases of summer 
 diarrhoea are produced by some such cause, and
 
 134 THE STORY OF GERM LIFE. 
 
 if they could be traced to their source would be 
 found to be produced by bacterial poisons swal- 
 lowed with food or drink, or by similar poisons 
 produced by bacteria growing in such food after 
 it is swallowed by the individual. In hot weather, 
 when bacteria are so abundant everywhere and 
 growing so rapidly, it is impossible to avoid such 
 dangers completely without exercising over all 
 food a guard which would be decidedly oppress- 
 ive. It is well to bear in mind, however, that 
 the most common and most dangerous source of 
 such poisons is milk or its products, and for this 
 reason one should hesitate to drink milk in hot 
 weather unless it is either quite fresh or has been 
 boiled to destroy its bacteria. 
 
 PATHOGENIC BACTERIA WHICH ARE TRUE 
 PARASITES. 
 
 This class of pathogenic bacteria includes 
 those which actually invade the body and feed 
 upon its tissues instead of living simply upon 
 swallowed food. It is difficult, however, to draw 
 
 any sharp line sep- 
 arating the two 
 classes. The bac- 
 teria which cause 
 diphtheria (Fig. 
 28 )> for instance, 
 do not really in- 
 
 FlG. ^.-Diphtheria bacillus. vade the body. 
 
 They grow in the 
 
 throat, attached to its walls, and are confined to 
 this external location or to the superficial tissues: 
 This bacillus is, in short, only found in the mouth 
 and throat, and is practically confined to the so-*
 
 PARASITIC BACTERIA. 135 
 
 called false membranes. It never enters any of 
 the tissues of the body, although attached to the 
 mucous membrane. It grows vigorously in this 
 membrane, and there secretes or in some way 
 produces extremely violent 
 poisons. These poisons 
 are then absorbed by the 
 body and give rise to the 
 general symptoms of the 
 disease. Much the same is 
 true of the bacillus which 
 causes tetanus or lockjaw YIG. ^.-Tetanus bacillus, 
 (Fig. 29). This bacillus is 
 
 commonly inoculated into the flesh of the victim 
 by a wound made with some object which has 
 been lying upon the earth where the bacillus 
 lives. The bacillus grows readily after being in- 
 oculated, but it is localized at the point of the 
 wound, without invading the tissue to any extent. 
 It produces, however, during its growth several 
 poisons which have been separated and studied. 
 Among them are some of the most violent poi- 
 sons of which we have any knowledge. While 
 the bacillus grows in the tissues around the 
 wound it secretes these poisons, which are then 
 absorbed by the body generally. Their poison- 
 ing effects produce the violent symptoms of the 
 disease. Of much the same nature is Asiatic 
 cholera. This is caused by a bacillus which is 
 able to grow rapidly in the intestines, feeding 
 perhaps in part on the food in the intestines and 
 perhaps in part upon the body secretions. To 
 a slight extent also it appears to be able to in- 
 vade the tissues of the body, for the bacilli are 
 found in the walls of the intestines. But it is 
 not a proper parasite, and the fatal disease it
 
 136 THE STORY OF GERM LIFE. 
 
 produces is the result of the absorption of the 
 poisons secreted in the intestines. 
 
 It is but a step from this to the true parasites. 
 Typhoid fever, for example, is a disease produced 
 by bacteria which grow in the intestines, but 
 which also invade the tissues 
 more extensively than the 
 cholera germs (Fig. 30). They 
 do not invade the body gen- 
 erally, however, but become 
 somewhat localized in special 
 glands like the liver, the 
 spleen, etc. Even here they 
 do not appear to find a very 
 favourable condition, for they 
 do not grow extensively in 
 these places. They are likely 
 to be found in the spleen in 
 small groups or centres, but 
 stained, showing the not generally distributed 
 cSres^b staged tnrou g h it: - Wherever they 
 toshowthe'flageiTa! grow they produce poison, 
 which has been called typho 
 toxine, and it is this poison chiefly which gives 
 rise to the fever. 
 
 Quite a considerable number of the patho- 
 genic germs are, like the typhoid bacillus, more 
 or less confined to special places. Instead of 
 distributing themselves through the body after 
 they find entrance, they are restricted to special 
 organs. The most common example of a para- 
 site of this sort is the tuberculosis bacillus, the 
 cause of consumption, scrofula, white swelling, 
 lupus, etc. (Fig. 31). Although this bacillus is 
 very common and is able to attack almost any 
 organ in the body, it is usually very restricted in
 
 PARASITIC BACTERIA. 
 
 137 
 
 growth. It may become localized in a small 
 gland, a single joint, a small spot in the lungs, or 
 in the glands of the mesentery, the other parts 
 of the body remaining free from infection. Not 
 infrequently the whole trouble is thus confined 
 
 flG. 31. Tuberculosis bacillus: a, As seen in lung tissue ; b, 
 More magnified ; c, As sometimes seen in sputum of con- 
 sumptive patients. 
 
 to such a small locality that nothing serious re- 
 sults. But in other instances the bacilli may after 
 a time slowly or rapidly distribute themselves 
 from these centres, attacking more and more of 
 the body until perhaps fatal results follow in the 
 end. This disease is therefore commonly of very 
 slow progress. 
 
 Again, we have still other parasites which are 
 not thus confined, but which, as soon as they 
 enter the body, produce a general infection, at- 
 tacking the blood and perhaps nearly all tissues 
 simultaneously. The most typical example of 
 this sort is anthrax or malignant pustule, a disease 
 fortunately rare in man (Fig. 32). Here the 
 bacilli multiply in the blood, and very soon a 
 general and fatal infection of the whole body 
 arises, resulting from the abundance of the ba-
 
 THE STORY OF GERM LIFE. 
 
 cilli everywhere. Some of the obscure diseases 
 known as blood poisoning appear to be of the same 
 general nature, 
 these diseases re- 
 sulting from a very 
 general invasion of 
 the whole body by 
 certain pathogenic 
 bacteria. 
 
 In general, then, 
 we see that the so- 
 called germ diseas- 
 es result from the 
 
 FIG. v.-Antkrax bacillus (splenic aCt j n , U P n . the 
 
 fever). body of poisons 
 
 produced by bac- 
 terial growth. Differences in the nature of these 
 poisons produce differences in the character of 
 the disease, and differences in the parasitic pow- 
 ers of the different species of bacteria produce 
 wide differences in the course of the diseases and 
 their relation to external phenomena. 
 
 WHAT DISEASES ARE DUE TO BACTERIA? 
 
 It is, of course, an extremely important matter 
 to determine to what extent human diseases are 
 caused by bacteria. It is not easy, nor indeed 
 possible, to do this to-day with accuracy. It is 
 no easy matter to prove that any particular dis- 
 ease is caused by bacteria. To do this it is neces- 
 sary to find some particular bacterium present in 
 all cases of the disease ; to find some method of 
 getting it to grow outside the body in culture 
 media; to demonstrate its absence in healthy ani- 
 mals, or healthy human individuals if it be a hu-
 
 PARASITIC BACTERIA, 
 
 139 
 
 man disease ; and, finally, to reproduce the disease 
 in healthy animals by inoculating them with the 
 bacterium. All of these steps of proof present 
 difficulties, but especially the last one. In the 
 study of animals it is comparatively easy to re- 
 produce a disease by inoculation. But experi- 
 ments upon man are commonly impossible, and 
 in the case of human diseases it is frequently 
 very difficult or impossible to obtain the final 
 test of the matter. After finding a specific bac- 
 terium associated with a disease, it is usually pos- 
 sible to experiment with it further upon animals 
 only. But some human diseases do not attack 
 animals, and in the case of diseases that may be 
 given to animals it is frequently uncertain wheth- 
 er the disease produced in the animal by such in- 
 oculation is identical with the human disease in 
 question, owing to the difference of symptoms in 
 the different animals. As a consequence, the proof 
 of the germ nature of different diseases varies all 
 the way from absolute demonstration to mere 
 suspicion. To give a complete and correct list 
 of the diseases caused by bacteria, or to give a 
 list of the bacteria species pathogenic to man, is 
 therefore at present impossible. 
 
 The difficulty of giving such a list is rendered 
 greater from the fact that we have in recent years 
 learned that the same species of pathogenic bac- 
 terium may produce different results under differ- 
 ent conditions. When the subject of germ dis- 
 ease was first studied and the connection between 
 bacteria and disease was first demonstrated, it 
 was thought that each particular species of 
 pathogenic bacteria produced a single definite 
 disease ; and conversely, each germ disease was 
 supposed to have its own definite species of bac-
 
 140 THE STORY OF GERM LIFE. 
 
 terium as its cause. Recent study has shown, 
 however, that this is not wholly true. It is true 
 that some diseases do have such a definite rela- 
 tion to definite bacteria. The anthrax germ, for 
 example, will always produce anthrax, no matter 
 where or how it is inoculated into the body. So, 
 also, in quite a number of other cases distinct 
 specific bacteria are associated with distinct dis- 
 eases. But, on the other hand, there are some 
 pathogenic bacteria which are not so definite in 
 their action, and produce different results in ac- 
 cordance with circumstances, the effect varying 
 both with the organ attacked and with the condi- 
 tion of the individual. For instance, a consider- 
 able number of different types of blood poison- 
 ing, septiccemia, pycemia, gangrene, inflammation of 
 wounds, or formation of pus from slight skin 
 wounds indeed, a host of miscellaneous trou- 
 bles, ranging all the way from a slight pus forma- 
 tion to a violent and severe blood poisoning all 
 appear to be caused by bacteria, and it is impos- 
 sible to make out any definite species associated 
 with the different types of these troubles. There 
 are three common forms of so-called pus cocci, 
 and these are found almost indiscriminately with 
 various types of inflammatory troubles. More- 
 over, these species of bacteria are found with al- 
 most absolute constancy in and around the body, 
 even in health. They are on the clothing, on the 
 skin, in the mouth and alimentary canal. Here 
 they exist, commonly doing no harm. They have, 
 however, the power of doing injury if by chance 
 they get into wounds. But their power of doing 
 injury varies both with the condition of the indi- 
 vidual and with variations in the bacteria them- 
 selves. If the individual is in a good condition
 
 PARASITIC BACTERIA. 141 
 
 of health these bacteria have little power of in- 
 juring him even when they do get into such 
 wounds, while at times of feeble vitality they 
 may do much more injury, and take the occasion 
 of any little cut or bruise to enter under the skin 
 and give rise to inflammation and pus. Some 
 people will develop slight abscesses or slight in- 
 flammations whenever the skin is bruised, while 
 with others such bruises or cuts heal at once 
 without trouble. Both are doubtless subject to 
 the same chance of infection, but the one resists, 
 while the other does not. In common parlance, 
 we say that such a tendency to abscesses indi- 
 cates a bad condition of the blood a phrase 
 which means nothing. Further, we find that the 
 same species of bacterium may have varying 
 powers of producing disease at different times. 
 Some species are universal inhabitants of the 
 alimentary canal and are ordinarily harmless, 
 while under other conditions of unknown char- 
 acter they invade the tissues and give rise to a 
 serious and perhaps fatal disease. We may thus 
 recognise some bacteria which may be compared 
 to foreign invaders, while others are domestic 
 enemies. The former, like the typhoid bacillus, 
 always produce trouble when they succeed in 
 entering the body and finding a foothold. The 
 latter, like the normal intestinal bacilli, are al- 
 ways present but commonly harmless, only under 
 special conditions becoming troublesome. All 
 this shows that there are other factors in deter- 
 mining the course of a disease, or even the exist- 
 ence of a disease, than the simple presence of a 
 peculiar species of pathogenic bacterium. 
 
 From the facts just stated it will be evident 
 that any list of germ diseases will be rather un- 
 10
 
 142 THE STORY OF GERM LIFE. 
 
 certain. Still, the studies of the last twenty years 
 or more have disclosed some definite relations of 
 bacteria and disease, and a list of the diseases 
 more or less definitely associated with distinct 
 species of bacteria is of interest. Such a list, 
 including only well-known diseases, is as follows : 
 
 Name of disease. Name of bacterium producing the disease. 
 
 Anthrax (Malignant pustule). Bacillus anthracis. 
 
 Cholera. 
 Croupous pneumonia. 
 Diphtheria. 
 Glanders. 
 Gonorrhoea. 
 Influenza. 
 Leprosy. 
 Relapsing fever. 
 Tetanus (lockjaw). 
 Tuberculosis (including con- 
 sumption, scrofula, etc.) 
 Typhoid fever. 
 
 Spirillum cholera asiatica. 
 Micrococcus pneumonia croufoseE. 
 Bacillus diphtheria. 
 Bacillus mallei. 
 Micrococcus gonorrhoea. 
 Bacillus of influenza. 
 Bacillus lepra. 
 Spirillum Obermeieri. 
 Bacillus tetani. 
 
 Bacillus tuberculosis. 
 Bacillus typhi abdominalis. 
 
 Various wound infections, including ^/fc^/mia, 
 
 pyaemia, acute abscesses, ulcers, erysipelas, etc., are pro- 
 duced by a few forms of micrococci, resembling 
 each other in many points but differing slightly. 
 They are found almost indiscriminately in any of 
 these wound infections, and none of them appears 
 to have any definite relation to any special form 
 of disease unless it be the micrococcus of erysip- 
 elas. The common pus micrococci are grouped 
 under three species, Staphylococcus pyogenes aureus, 
 Staphylococcus pyogenes, and Streptococcus pyogenes. 
 These three are the most common, but others are 
 occasionally found. 
 
 In addition to these, which may be regarded as 
 demonstrated, the following diseases are with 
 more or less certainty regarded as caused by dis- 
 tinct specific bacteria : Bronchitis, endocarditis,
 
 PARASITIC BACTERIA. 143 
 
 measles, whooping-cough, peritonitis, pneumonia, 
 syphilis. 
 
 Still another list might be given of diseases 
 whose general nature indicates that they are 
 caused by bacteria, but in connection with which 
 no distinct bacterium has yet been found. As 
 might be expected also, a larger list of animal 
 diseases has been demonstrated to be caused by 
 these organisms. In addition, quite a number 
 of species of bacteria have been found in such 
 material as faeces, putrefying blood, etc., which 
 have been shown by experiment to be capable of 
 producing diseases in animals, but in regard to 
 which we have no evidence that they ever do 
 produce actual disease under any normal con- 
 ditions. These may contribute, perhaps, to the 
 troubles arising from poisonous foods, but can 
 not be regarded as disease germs proper. 
 
 VARIABILITY OF PATHOGENIC POWERS. 
 
 As has already been stated, our ideas of the 
 relation of bacteria to disease have undergone 
 quite a change since they were first formulated, 
 and we recognise other factors influencing dis- 
 ease besides the actual presence of the bac- 
 terium. These we may briefly consider under 
 two heads, viz., variation in the bacterium, and 
 variation in the susceptibility of the individual. 
 The first will require only a brief consideration. 
 
 That the same species of pathogenic bacteria 
 at different times varies in its powers to produce 
 disease has long been known. Various con- 
 ditions are known to affect thus the virulence of 
 bacteria. The bacillus which is supposed to give 
 rise to pneumonia loses its power to produce the
 
 144 THE STORY OF GERM LIFE. 
 
 disease after having been cultivated for a short 
 time in ordinary culture media in the laboratory. 
 This is easily understood upon the suggestion 
 that it is a parasitic bacillus and does not thrive 
 except under parasitic conditions. Its patho- 
 genic powers can sometimes be restored by pass- 
 ing it again through some susceptible animal. 
 One of the most violent pathogenic bacteria is 
 that which produces anthrax, but this loses its 
 pathogenic powers if it is cultivated for a con- 
 siderable period at a high temperature. The 
 micrococcus which causes fowl cholera loses its 
 power if it be cultivated in common culture media, 
 care being taken to allow several days to elapse 
 between the successive inoculations into new 
 culture flasks. Most pathogenic bacteria can 
 in some way be so treated as to suffer a dimi- 
 nution or complete loss of their powers of pro- 
 ducing a fatal disease. On the other hand, other 
 conditions will cause an increase in the virulence 
 of a pathogenic germ. The virus which produces 
 hydrophobia is increased in violence if it is 
 inoculated into a rabbit and subsequently taken 
 from the rabbit for further inoculation. The 
 fowl cholera micrococcus, which has been weak- 
 ened as just mentioned, may be restored to its 
 original violence by inoculating it into a small 
 bird, like a sparrow, and inoculating a second 
 bird from this. A few such inoculations will 
 make it as active as ever. These variations 
 doubtless exist among the species in Nature as 
 well as in artificial cultures. The bacteria 
 which produce the various wound infections and 
 abscesses, etc., appear to vary under normal con- 
 ditions from a type capable of producing violent 
 and fatal blood poisoning to a type producing
 
 PARASITIC BACTERIA. 145 
 
 only a simple abscess, or even to a type that is 
 entirely innocuous. It is this factor, doubtless, 
 which in a large measure determines the severity 
 of any epidemic of a bacterial contagious dis- 
 ease. 
 
 SUSCEPTIBILITY OF THE INDIVIDUAL. 
 
 The very great modification of our early 
 views has affected our ideas as to the power 
 which individuals have of resisting the invasion 
 of pathogenic bacteria. It has from the first 
 been understood that some individuals are more 
 susceptible to disease than others, and in attempt- 
 ing to determine the significance of this fact 
 many valuable and interesting discoveries have 
 been made. After the exposure to the disease 
 there follows a period of some length in which 
 there are no discernible effects. This is followed 
 by the onset of the disease and its development 
 to a crisis, and, if this be passed, by a recovery. 
 The general course of a germ disease is divided 
 into three stages: the stage of incubation, the 
 development of the disease, and the recovery. The 
 susceptibility of the body to a disease may be 
 best considered under the three heads of Inva- 
 sion, Resistance, Recovery. 
 
 Means of Invasion. In order that a germ dis- 
 ease should arise in an individual, it is first ne- 
 cessary that the special bacterium which causes 
 the disease should get into the body. There 
 are several channels through which bacteria can 
 thus find entrance ; these are through the 
 mouth, through the nose, through the skin, and 
 occasionally through excretory ducts. Those 
 which come through the mouth come with the
 
 146 THE STORY OF GERM LIFE. 
 
 food or drink which we swallow ; those which 
 enter through the nose must be traced to the air; 
 and those which enter through the skin come in 
 most cases through contact with some infected 
 object, such as direct contact with the body of 
 an infected person or his clothing or some objects 
 he has handled, etc. Occasionally, perhaps, the 
 bacteria may get into the skin from the air, but 
 this is certainly uncommon and confined to a few 
 diseases. There are here two facts of the utmost 
 importance for every one to understand: first, 
 that the chance of disease bacteria being carried 
 to us through the air is very slight and confined 
 to a few diseases, such as smallpox, tuberculo- 
 sis, scarlet fever; etc., and, secondly, that the un- 
 injured skin and the uninjured mucous membrane 
 also is almost a sure protection against the in- 
 vasion of the bacteria. If the skin is whole, 
 without bruises or cuts, bacteria can seldom, if 
 ever, find passage through it. These two facts 
 are of the utmost importance, since of all sources 
 of infection we have the least power to guard 
 against infection through the air, and since of all 
 means of entrance we can guard the skin with 
 the greatest difficulty. We can easily render 
 food free from pathogenic bacteria by heating it. 
 The material we drink can similarly be rendered 
 harmless, but we can not by any known means 
 avoid breathing air, nor is there any known 
 method of disinfecting the air, and it is impos- 
 sible for those who have anything to do with 
 sick persons to avoid entirely having contact 
 either with the patient or with infected clothing 
 or utensils. 
 
 From the facts here given it will be seen that 
 the individual's susceptibility to disease produced
 
 PARASITIC BACTERIA. 147 
 
 by parasitic bacteria will depend upon his habits 
 of cleanliness, his care in handling infectious 
 material, or care in cleansing the hands after such 
 handling, upon his habit of eating food cooked 
 or raw, and upon the condition of his skin and 
 mucous membranes, since any kind of bruises 
 wjll increase susceptibility. Slight ailments, 
 such as colds, which inflame the mucous mem- 
 brane, will decrease its resisting power and ren- 
 der the individual more susceptible to the entrance 
 of any pathogenic germs should they happen to 
 be present. Sores in the mouth or decayed teeth 
 may in the same way be prominent factors in- the 
 individual's susceptibility. Thus quite a number 
 of purely physical factors may contribute to an 
 individual's susceptibility. 
 
 Resisting Power of the Body. Even after the 
 bacteria get into the body it is by no means cer- 
 tain that they will give rise to disease, for they 
 have now a battle to fight before they can be sure 
 of holding their own. It is now, indeed, that the 
 actual conflict between the powers of the body 
 and these microscopic invaders begins. After 
 they have found entrance into the body the bac- 
 teria have arrayed against them strong resisting 
 forces of the human organism, endeavouring to 
 destroy and expel them. Many of them are rapid- 
 ly killed, and sometimes they are all destroyed 
 without being able to gain a foothold. In such 
 cases, of course, no trouble results. In other 
 cases the body fails to overcome the powers of 
 the invaders and they eventually multiply rapidly. 
 In this struggle the success of the invaders is not 
 necessarily a matter of numbers. They are sim- 
 ply struggling to gain a position in the body, where 
 they can feed and grow. A few individuals may
 
 148 THE STORY OF GERM LIFE. 
 
 be entirely sufficient to seize such a foothold, and 
 then these by multiplying may soon become in- 
 definitely numerous. To protect itself, therefore, 
 the human body must destroy every individual 
 bacterium, or at least render them all incapa- 
 ble of growth. Their marvellous reproductive 
 powers give the bacteria an advantage in the bat- 
 tle. On the other hand, it takes time even for 
 these rapidly multiplying beings to become suf- 
 ficiently numerous to do injury. There is thus an 
 interval after their penetration into the body 
 when these invaders are weak in numbers. Dur- 
 ing this interval the period of incubation the 
 body may organize a resistance sufficient to ex- 
 pel them. 
 
 We do not as yet thoroughly understand the 
 forces which the human organism is able to array 
 against these invading foes. Some of its meth- 
 ods of defence are, however, already intelligible 
 to us, and we know enough, at all events, to give 
 us an idea of the intensity of the conflict that is 
 going on, and of the vigorous and powerful forces 
 which the human organism is able to bring against 
 its invading enemies. 
 
 In the first place, we notice that a majority of 
 bacteria are utterly unable to grow in the human 
 body even if they do find entrance. There are 
 known to bacteriologists to-day many hundreds, 
 even thousands of species, but the vast majority 
 of these find in the human tissues conditions so 
 hostile to their life that they are utterly unable to 
 grow therein. Human flesh or human blood will 
 furnish excellent food for them if the individual 
 be dead, but living human flesh and blood in some 
 way exerts a repressing influence upon them which 
 is fatal to the growth of a vast majority of spe-
 
 PARASITIC BACTERIA. 149 
 
 cies. Some few species, however, are not thus 
 destroyed by the hostile agencies of the tissues 
 of the animal, but are capable of growing and 
 multiplying in the living body. These alone are 
 what constitute the pathogenic bacteria, since, of 
 course, these are the only bacteria which can pro- 
 duce disease by growing in the tissues of an ani- 
 mal. The fact that the vast majority of bacteria 
 can not grow in the living organism shows clearly 
 enough that there are some conditions existing in 
 the living tissue hostile to bacterial life. There 
 can be little doubt, moreover, that it is these same 
 hostile conditions, which enable the body to resist 
 the attack of the pathogenic species in cases 
 where resistance is successfully made. 
 
 What are the forces arrayed against these in- 
 vaders ? The essential nature of the battle ap- 
 pears to be a production of poisons and counter 
 poisons. It appears to be an undoubted fact that 
 the first step in repelling these bacteria is to flood 
 them with certain poisons which check their 
 growth. In the blood and lymph of man and 
 other animals there are present certain products 
 which have a direct deleterious influence upon the 
 growth of micro-organisms. The existence of 
 these poisons is undoubted, many an experiment 
 having directly attested to their presence in the 
 blood of animals. Of their nature we know very 
 little, but of their repressing influence upon bac- 
 terial growth we are sure. They have been named 
 alexines, and they are produced in the living tis- 
 sue, although as to the method of their pro- 
 duction we are in ignorance. By the aid of 
 these poisons the body is able to prevent the 
 growth of the vast majority of bacteria which 
 get into its tissues. Ordinary micro-organisms
 
 150 THE STORY OF GERM LIFE. 
 
 are killed at once, for these alexines act as anti- 
 septics, and common bacteria can no more grow 
 in the living body than they could in a solution 
 containing other poisons. Thus the body has a 
 perfect protection against the majority of bac- 
 teria. The great host of species which are found 
 in water, milk, air, in our mouths or clinging to 
 our skin, and which are almost omnipresent in 
 Nature, are capable of growing well enough in or- 
 dinary lifeless organic foods ; but just as soon as 
 they succeed in finding entrance into living human 
 tissue their growth is checked at once by these 
 antiseptic agents which are poured upon them. 
 Such bacteria are therefore not pathogenic germs, 
 and not sources of trouble to human health. 
 
 There are, on the other hand, a few species of 
 bacteria which may be able to retain their lodg- 
 ment in the body in spite of this attempt of the 
 individual to get rid of them. These, of course, 
 constitute the pathogenic species, or so-called 
 " disease germs." Only such species as can over- 
 come this first resistance can be disease germs, 
 for they alone can retain their foothold in the 
 body. 
 
 But how do these species overcome the poi- 
 sons which kill the other harmless bacteria ? 
 They, as well as the harmless forms, find these 
 alexines injurious to their growth, but in some 
 way they are able to counteract the poisons. In 
 this general discussion of poisons we are dealing 
 with a subject which is somewhat obscure, but 
 apparently the pathogenic bacteria are able to 
 overcome the alexines of the body by producing 
 in their turn certain other products which neu- 
 tralize the alexines, thus annulling their action. 
 These pathogenic bacteria, when they get into
 
 PARASITIC BACTERIA. 151 
 
 the body, give rise at once to a group of bodies 
 which have been named lysines. These lysines 
 are as mysterious to us as the alexines, but they 
 neutralize the effect of the alexines and thus 
 overcome the resistance the body offers to bac- 
 terial growth. The invaders can now multiply 
 rapidly enough to get a lasting foothold in the 
 body and then soon produce the abnormal symp- 
 toms which we call disease. Pathogenic bacteria 
 thus differ from the non-pathogenic bacteria 
 primarily in this power of secreting products 
 which can neutralize the ordinary effects of the 
 alexines, and so overcome the body's normal re- 
 sistance to their parasitic life. 
 
 Even if the bacteria do thus overcome the 
 alexines the battle is not yet over, for the indi- 
 vidual has another method of defence which is 
 now brought into activity to check the growth of 
 the invading organisms. This second method of 
 resistance is by means of a series of active cells 
 found in the blood, known as white blood-cor- 
 puscles (Fig. 33 a, fr). They are minute bits of 
 protoplasm present in the blood and lymph in 
 large quantities. They are active cells, capable 
 of locomotion and able to crawl out of the blood- 
 vessels. Not infrequently they are found to take 
 into their bodies small objects with which they 
 come in contact. One of their duties is thus to en- 
 gulf minute irritating bodies which may be in the 
 tissues, and to carry them away for excretion. 
 They thus act as scavengers. These corpuscles 
 certainly have some agency in warding off the at- 
 tacks of pathogenic bacteria. Very commonly 
 they collect in great numbers in the region of 
 the body where invading bacteria are found. Such 
 invading bacteria exert upon them a strong attrac-
 
 
 THE STORY OF GERM LIFE. 
 
 Pie. 33. White blood corpuscles and other phagocytes : a, A sta- 
 tionary form ; b, Motile form ; c, Phagocyte with a bacterium 
 half engulfed ; d, Phagocytes containing bacteria either dead 
 or alive ; e, Phagocyte loaded with bacteria.
 
 PARASITIC BACTERIA. 153 
 
 tion, and the corpuscles leave the blood-vessels 
 and sometimes form a solid phalanx completely 
 surrounding the invading germs. Their collec- 
 tion at these points may make itself seen exter- 
 nally by the phenomenon we call inflammation. 
 
 There is no question that the corpuscles en- 
 gage in conflict with the bacteria when they thus 
 surround them. There has been not a little dis- 
 pute, however, as to the method by which they 
 carry on the conflict. It has been held by some 
 that the corpuscles actually take the bacteria into 
 their bodies, swallow them, as it were, and subse- 
 quently digest them (Fig. 33 c, d, e). This idea 
 gave rise to the theory of phagocytosis, and the 
 corpuscles were consequently named phagocytes. 
 The study of several years has, however, made it 
 probable that this is not the ordinary method by 
 which the corpuscles destroy the bacteria. Ac- 
 cording to our present knowledge the method is 
 a chemical one. These cells, when they thus col- 
 lect in quantities around the invaders, appear to 
 secrete from their own bodies certain injurious 
 products which act upon the bacteria much as do 
 the alexines already mentioned. These new bod- 
 ies have a decidedly injurious effect upon the 
 multiplying bacteria ; they rapidly check their 
 growth, and, acting in union with the alexines, 
 may perhaps entirely destroy them. 
 
 After the bacteria are thus killed, the white 
 blood-corpuscles may load themselves with their 
 dead bodies and carry them away (Fig. 33 d, e). 
 Sometimes they pass back into the blood stream 
 and carry the bacteria to various parts of the 
 body for elimination. Not infrequently the white 
 corpuscles die in the contest, and then may ac- 
 cumulate in the form of pus and make their way
 
 1 54 THE STORY OF GERM LIFE. 
 
 through the skin to be discharged directly. The 
 battle between these phagocytes and the bacteria 
 goes on vigorously. If in the end the phagocytes 
 prove too strong for the invaders, the bacteria 
 are gradually all destroyed, and the attack is re- 
 pelled. Under these circumstances the individual 
 commonly knows nothing of the matter. This 
 conflict has taken place entirely without any con- 
 sciousness on his part, and he may not even know 
 that he has been exposed to the attack of the 
 bacteria. In other cases the bacteria prove too 
 strong for the phagocytes. They multiply too 
 rapidly, and sometimes they produce secretions 
 which actually drive the phagocytes away. Com- 
 monly, as already noticed, the corpuscles are at- 
 tracted to the point of invasion, but in some cases, 
 when a particularly deadly and vigorous species 
 of bacteria invades the body, the secretions pro- 
 duced by them are so powerful as actually to 
 drive the corpuscles away. Under these circum- 
 stances the invading hosts have a chance to mul- 
 tiply unimpeded, to distribute themselves over the 
 body, and the disease rapidly follows as the result 
 of their poisoning action on the body tissues. 
 
 It is plain, then, that the human body is not 
 helpless in the presence of the bacteria of disease, 
 but that it is supplied with powerful resistant 
 forces. It must not be supposed, however, that 
 the outline of the action of these forces just given 
 is anything like a complete account of the matter; 
 nor must it be inferred that the resistance is in all 
 respects exactly as outlined. The subject has only 
 recently been an object of investigation, and we are 
 as yet in the dark in regard to many of the facts. 
 The future may require us to modify to some ex- 
 tent even the brief outline which has been given.
 
 PARASITIC BACTERIA. 155 
 
 But while we recognise this uncertainty in the de- 
 tails, we may be assured of the general facts. 
 The living body has some very efficacious resist- 
 ant forces which prevent most bacteria from 
 growing within its tissues, and which in large 
 measure may be relied upon to drive out the true 
 pathogenic bacteria. These resistant forces are 
 in part associated with the productions of body 
 poisons, and are in part associated with the active 
 powers of special cells which have been called 
 phagocytes. The origin of the poisons and the 
 exact method of action of the phagocytes we may 
 well leave to the future to explain. 
 
 These resisting powers of the body will vary 
 with conditions. It is evident that they are 
 natural powers, and they will doubtless vary with 
 the general condition of vigour of the individual. 
 Robust health, a body whose powers are strong, 
 well nourished, and vigorous, will plainly furnish 
 the conditions for the greatest resistance to bac- 
 terial diseases. One whose bodily activities are 
 weakened by poor nutrition can offer less resist- 
 ance. The question whether one shall suffer 
 from a germ disease is not simply the question 
 whether he shall be exposed, or even the question 
 whether the bacteria shall find entrance into his 
 body. It is equally dependent upon whether he 
 has the bodily vigour to produce alexinesin proper 
 quantity, or to summon the phagocytes in suffi- 
 cient abundance and vigour to ward off the attack. 
 We may do much to prevent disease by sanitation, 
 which aids in protecting the individual from at- 
 tack ; but we must not forget that the other half 
 of the battle is of equal importance, and hence 
 we must do all we can to strengthen the resist- 
 ing forces of the organism.
 
 156 THE STORY OF GERM LIFE. 
 
 RECOVERY FROM GERM DISEASES. 
 
 These resisting forces are not always sufficient 
 to drive off the invaders. The organisms may 
 retain their hold in the body for a time and 
 eventually break down the resistance. After this 
 they may multiply unimpeded and take entire 
 possession of the body. As they become more 
 numerous their poisonous products increase and 
 begin to produce direct poisoning effects on the 
 body. The incubation period is over and the dis- 
 ease comes on. The disease now runs its course. 
 It becomes commonly more and more severe until 
 a crisis is reached. Then, unless the poisoning is 
 so severe that death occurs, the effects pass away 
 and recovery takes place. 
 
 But why should not a germ disease be always 
 fatal ? If the bacteria thus take possession of the 
 body and can grow there, why do they not always 
 continue to multiply until they produce sufficient 
 poison to destroy the life of the individual ? 
 Such fatal results do, of course, occur, but in by 
 far the larger proportion of cases recovery finally 
 takes place. 
 
 Plainly, the body must have another set of 
 resisting forces which is concerned in the final 
 recovery. Although weakened by the poisoning 
 and suffering from the disease, it does not yield 
 the battle, but somewhat slowly organizes a new 
 attack upon the invaders. For a time the multi- 
 plying bacteria have an unimpeded course and 
 grow rapidly ; but finally their further increase is 
 checked, their vigour impaired, and after this they 
 diminish in numbers and are finally expelled from 
 the body entirely. Of the nature of this new re- 
 sistance but little is yet known. We notice, in
 
 PARASITIC BACTERIA. 15 
 
 the first place, that commonly after such a recov- 
 ery the individual has decidedly increased resist- 
 ance to the disease. This increased resistance 
 may be very lasting, and may be so considerable 
 as to give almost complete immunity from the 
 disease for many years, or for life. One attack 
 of scarlet fever gives the individual great immu- 
 nity for the future. On the other hand, the re- 
 sistance thus derived may be very temporary, as 
 in the case of diphtheria. But a certain amount 
 of resistance appears to be always acquired. 
 This power of resisting the activities of the para- 
 sites seems to be increased during the progress 
 of the disease, and, if it becomes sufficient, it 
 finally drives off the bacteria before they have 
 produced death. After this, recovery takes place. 
 To what this newly acquired resisting power is 
 due is by no means clear to bacteriologists, al- 
 though certain factors are already known. It 
 appears beyond question that in the case of cer- 
 tain diseases the cells of the body after a time 
 produce substances which serve as antidotes to 
 the poisons produced by the bacteria during their 
 growth in the body antitoxines. In the case of 
 diphtheria, for instance, the germs growing in the 
 throat produce poisons which are absorbed by the 
 body and give rise 'to the symptoms of the dis- 
 ease; but after a time the body cells react, and 
 themselves produce a counter toxic body which 
 neutralizes the poisonous effect of the diphtheria 
 poison. This substance has been isolated from 
 the blood of animals that have recovered from an 
 attack of diphtheria, and has been called diphthe- 
 ria antitoxine. But even with this knowledge the 
 recovery is not fully explained. This antitoxine 
 neutralizes the effects of the diphtheria toxine, 
 11
 
 158 THE STORY OF GERM LIFE. 
 
 and then the body develops strength to drive off 
 the bacteria which have obtained lodgment in the 
 throat. How they accomplish this latter achieve- 
 ment we do not know as yet. The antitoxine 
 developed simply neutralizes the effects of the 
 toxine. Some other force must be at work to get 
 rid of the bacteria, a force which can only exert 
 itself after the poisoning effect of the poison is 
 neutralized. In these cases, then, the recovery is 
 due, first, to the development in the body of the 
 natural antidotes to the toxic poisons, and, second, 
 to some other unknown force which drives off the 
 parasites. 
 
 These facts are certainly surprising. If one 
 had been asked to suggest the least likely theory 
 to explain recovery from disease, he could hardly 
 have found one more unlikely than that the body 
 cells developed during the disease an antidote to 
 the poison which the disease bacteria were pro- 
 ducing. Nevertheless, it is beyond question that 
 such antidotes are formed during the course of 
 the germ diseases. It has not yet been shown in 
 all diseases, and it would be entirely too much to 
 claim that this is the method of recovery in all 
 cases. We may say, however, in regard to bacte- 
 rial diseases in general, that after the bacteria en- 
 ter the body at some weak point they have first a 
 battle to fight with the resisting powers of the body, 
 which appear to be partly biological and partly 
 chemical. These resisting powers are in many 
 cases entirely sufficient to prevent the bacteria 
 from obtaining a foothold. If the invading host 
 overcome the resisting powers, then they begin 
 to multiply rapidly, and take possession of the 
 body or some part of it. They continue to grow 
 until either the individual dies or something oc-
 
 PARASITIC BACTERIA. 159 
 
 curs to check their growth. After the individual 
 develops the renewed powers of checking their 
 growth, recovery takes place, and the individual 
 is then, because of these renewed powers of re- 
 sistance, immune from a second attack of the dis- 
 ease for a variable length of time. 
 
 This, in the merest outline, represents the rela- 
 tion of bacterial parasites to the human body. 
 But while this is a fair general expression of the 
 matter, it must be recognised that different dis- 
 eases differ much in their relations, and no general 
 outline will apply to all. They differ in their 
 method of attack and in the point of attack. Not 
 only do they produce different kinds of poisons 
 giving rise to different symptoms of poisoning ; 
 not only do they produce different results in dif- 
 ferent animals ; not only do the different patho- 
 genic species differ much in their power to de- 
 velop serious disease, but the different species are 
 very particular as to what species of animal they 
 attack. Some of them can live as parasites in 
 man alone; some can live as parasites upon man 
 and the mouse and a few other animals; some 
 can live in various animals but not in man ; some 
 appear to be able to live in the field mouse, but 
 not in the common mouse ; some live in the horse; 
 some in birds, but not in warm-blooded mammals ; 
 while others, again, can live almost equally well 
 in the tissues of a long list of animals. Those 
 which can live as parasites upon man are, of 
 course, especially related to human disease, and 
 are of particular interest to the physician, while 
 those which live in animals are in a similar way 
 of interest to veterinarians. 
 
 Thus we see that parasitic bacteria show the 
 widest variations. They differ in point of attack,
 
 160 THE STORY OF GERM LIFE. 
 
 in method of attack, and in the part ot the body 
 which they seize upon as a nucleus for growth. 
 They differ in violence and in the character of the 
 poisons they produce, as well as in their power of 
 overcoming the resisting powers of the body. 
 They differ at different times in their powers of 
 producing disease. In short, they show such a 
 large number of different methods of action that 
 no general statements can be made which will ap- 
 ply universally, and no one method of guarding 
 against them or in driving them off can be hoped 
 to apply to any extended list of diseases. 
 
 DISEASES CAUSED BY OTHER ORGANISMS THAN 
 BACTERIA. 
 
 Although the purpose of this work is to deal 
 primarily with the bacterial world, it would hardly 
 be fitting to leave the subject without some refer- 
 ence to diseases caused by organisms which do 
 not belong to the group of bacteria. While most 
 of the so-called germ diseases are caused by the 
 bacteria which we have been studying in the 
 previous chapters, there are some whose inciting 
 cause is to be found among organisms belonging 
 to other groups. Some of these are plants of a 
 higher organization than bacteria, but others are 
 undoubtedly microscopic animals. Their life 
 habits are somewhat different from those of 
 bacteria, and hence the course of the diseases is 
 commonly different. Of the diseases thus pro- 
 duced by microscopic animals or by higher plants, 
 one or two are of importance enough to deserve 
 special mention here. 
 
 Malaria. The most important of these dis- 
 eases is malaria in its various forms, and known
 
 PARASITIC BACTERIA. 
 
 161 
 
 under various names chills and fever, autumnal 
 fever, etc. This disease, so common almost 
 everywhere, has been studied by physicians and 
 scientists for a long time, and many have been 
 the causes assigned to it. At one time it was 
 thought to be the result of the growth of a bacte- 
 rium, and a distinct bacillus was described as pro- 
 ducing it. It has finally been shown, however, 
 to be caused by a microscopic organism belong- 
 ing to the group of unicellular animals, and some- 
 
 FlG. 34. Malarial organism : Figs, a to g show the growth of 
 the parasite within the blood corpuscle ; o is the organism in 
 all cases ; s, the spores. Fig. i is the so-called cresentic body 
 which develops through Fig. 2, into the flagellate form, shown 
 at 3. The significance of i, 2, and 3 are not known. 
 
 what closely related to the well-known amoeba. 
 This organism is shown in Fig. 34. The whole 
 history of the malarial organism is not yet known. 
 The following statements comprise the most im- 
 portant facts known in regard to it, and its rela- 
 tion to the disease in man. 
 
 Undoubtedly the malarial germ has some 
 home outside the human body, but it is not yet 
 very definitely known what this external home is; 
 nor do we know from what source the human para-
 
 162 THE STORY OF GERM LIFE. 
 
 site is derived. It appears probable that water 
 serves in some cases as its means of transference 
 to man, and air in other cases. From some ex- 
 ternal source it gains access to man and finds 
 its way into the blood. Here it attacks the 
 red blood-corpuscles, each malarial organism 
 making its way into a single one (Fig. 34 a). 
 Here it now grows, increasing in size at the 
 expense of the substance of the corpuscle 
 (Fig. 34 a-f). As it becomes larger it becomes 
 granular, and soon shows a tendency to separate 
 into a number of irregular masses (Fig. 34 /). 
 Finally it breaks up into many minute bodies 
 called spores (Fig. 34^). These bodies break out 
 of the corpuscle and for a time live a free life in 
 the blood (Fig. 34 ti). After a time they make 
 their way into other red blood-corpuscles, develop 
 into new malarial amoeboid parasites, and repeat 
 the growth and sporulation. This process can ap- 
 parently be repeated many times without check. 
 
 These organisms are thus to be regarded as 
 parasites of the red corpuscles. It is, of course, 
 easy to believe that an extensive parasitism and 
 destruction of the corpuscles would be disastrous 
 to the health of the individual, and the severity 
 of the disease will depend upon the extent of the 
 parasitism. Corresponding to this life history of 
 the organism, the disease malaria is commonly 
 characterized by a decided intermittency, periods 
 of chill and fever alternating with periods of in- 
 termission in which these symptoms are abated. 
 The paroxysms of the disease, characterized by 
 the chill, occur at the time that the spores are 
 escaping from the blood-corpuscles and floating 
 in the blood. After they have again found their 
 way into a blood-corpuscle the fever diminishes,
 
 PARASITIC BACTERIA. 163 
 
 and during their growth in the corpuscle until 
 the next sporulation the individual has a rest 
 from the more severe symptoms. 
 
 There appears to be more than one variety of 
 the malarial organism, the different types differ- 
 ing in the length of time it takes for their growth 
 and sporulation. There is one variety, the most 
 common one, which requires two days for its 
 growth, thus giving rise to the paroxysm of the 
 disease about once in forty-eight hours ; another 
 variety appears to require three days for its 
 growth ; while still another variety appears to be 
 decidedly irregular in its period of growth and 
 sporulation. These facts readily explain some of 
 the variations in the disease. Certain other ir- 
 regularities appear to be due to a different cause. 
 More than one brood of parasites may be in the 
 blood of the individual at the same time, one 
 producing sporulation at one time and another at 
 a different time. Such a simultaneous growth of 
 two independent broods may plainly produce al- 
 most any kind of modification in the regularity of 
 the disease. 
 
 The malarial organism appears to be very 
 sensitive to quinine, a very small quantity being 
 sufficient to kill it. Upon this point depends the 
 value of quinine as a medicine. If the drug be 
 present in the blood at the time when the spores 
 are set free from the blood-corpuscle, they are 
 rapidly killed by it before they have a chance to 
 enter another corpuscle. During their growth in 
 the corpuscle they are far less sensitive to qui- 
 nine than when they exist in the free condition as 
 spores, and at this time the drug has little effect. 
 
 The malarial organism is an animal, and can 
 not be cultivated in the laboratory by any arti-
 
 1 64 THE STORY OF GERM LIFE. 
 
 ficial method yet devised. Its whole history is 
 therefore not known. It doubtless has some 
 home outside the blood of animals, and very 
 likely it may pass through other stages of a meta- 
 morphosis in the bodies of other animals. Most 
 parasitic animals have two or more hosts upon 
 which they live, alternating from one to the other, 
 and that such is the case with the malarial para- 
 site is at least probable. But as yet bacteriolo- 
 gists have been unable to discover anything very 
 definite in regard to the matter. Until we can 
 learn something in regard to its life outside the 
 blood of man we can do little in the way of devis- 
 ing methods to avoid it. 
 
 Malaria differs from most germ diseases in the 
 fact that the organisms which produce it are not 
 eliminated from the body in any way. In most 
 germ diseases the germs are discharged from the 
 patient by secretions or excretions of some kind, 
 and from these excretions may readily find their 
 way into other individuals. The malarial organ- 
 ism is not discharged from the body in any way, 
 and hence is not contagious. If the parasite does 
 pass part of its history in some other animal 
 than man, there must be some means by which it 
 passes from man to its other host. It has been 
 suggested that some of the insects which feed 
 upon human blood may serve as the second host 
 and become inoculated when feeding upon such 
 blood. This has been demonstrated with start- 
 ling success in regard to the mosquito (Anopheles), 
 some investigators going so far as to say that this 
 is the only way in which the disease can be com- 
 municated. 
 
 Several other microscopic animals occur as 
 parasites upon man, and some of them are so 
 definitely associated with certain diseases as to
 
 COMBATING PARASITIC BACTERIA. 165 
 
 lead to the belief that they are the cause of these 
 diseases. The only one of very common occur- 
 rence is a species known as Amoeba coli, which is 
 found in cases of dysentery. In a certain type 
 of dysentery this organism is so universally found 
 that there is little doubt that it is in some very 
 intimate way associated with the cause of the dis- 
 ease. Definite proof of the matter is, however, 
 as yet wanting. 
 
 On the side of plants, we find that several 
 plants of a higher organization than bacteria may 
 become parasitic upon the body of man and pro- 
 duce various types of disease. These plants be- 
 long mostly to the same group as the moulds, 
 and they are especially apt to attack the skin. 
 They grow in the skin, particularly under the hair, 
 and may send their threadlike branches into some 
 of the subdermal tissues. This produces irrita- 
 tion and inflammation of the skin, resulting in 
 trouble, and making sores difficult to heal. So 
 long as the plant continues to grow, the sores, of 
 course, can not be healed, and when the organ- 
 isms get into the skin under the hair it is fre- 
 quently difficult to destroy them. Among the 
 diseases thus caused are ringworm, thrush, alopecia, 
 etc. 
 
 CHAPTER VI. 
 
 METHODS OF COMBATING PARASITIC BACTERIA. 
 
 THE chief advantage of knowing the cause of 
 disease is that it gives us a vantage ground from 
 which we may hope to find means of avoiding its 
 evils. The study of medicine in the past history
 
 1 66 THE STORY OF GERM LIFE. 
 
 of the world has been almost purely empirical, 
 with a very little of scientific basis. Great hopes 
 are now entertained that these new facts will place 
 this matter upon a more strictly scientific foun- 
 dation. Certainly in the past twenty-five years, 
 since bacteriology has been studied, more has 
 been done to solve problems connected with dis- 
 ease than ever before. This new knowledge has 
 been particularly directed toward means of avoid- 
 ing disease. Bacteriology has thus far borne 
 fruit largely in the line of preventive medicine, 
 although to a certain extent also along the line 
 of curative medicine. This chapter will be de- 
 voted to considering how the study of bacteriol- 
 ogy has contributed directly and indirectly to 
 our power of combating disease. 
 
 PREVENTIVE MEDICINE. 
 
 In the study of medicine in the past centuries 
 the only aim has been to discover methods of 
 curing disease ; at the present time a large and 
 increasing amount of study is devoted to the 
 methods of preventing disease. Preventive medi- 
 cine is a development of the last few years, and 
 is based almost wholly upon our knowledge of 
 bacteria. This subject is yearly becoming of 
 more importance. Forewarned is forearmed, and 
 it has been found that to know the cause of a 
 disease is a long step toward avoiding it. As 
 some of our contagious and epidemic diseases 
 have been studied in the light of bacteriological 
 knowledge, it has been found possible to deter- 
 mine not only their cause, but also how infection 
 is brought about, and consequently how conta- 
 gion may be avoided. Some of the results which
 
 COMBATING PARASITIC BACTERIA. 167 
 
 have grown up so slowly as to be hardly appre- 
 ciated are really great triumphs. For instance, 
 the study of bacteriology first led us to suspect, 
 and then demonstrated, that tuberculosis is a 
 contagious disease, and from the time that this 
 was thus proved there has been a slow, but, it is 
 hoped, a sure decline in this disease. Bacterio- 
 logical study has shown that the source of chol- 
 era infection in cases of raging epidemics is, in 
 large part at least, our drinking water ; and since 
 this has been known, although cholera has twice 
 invaded Europe, and has been widely distributed, 
 it has not obtained any strong foothold or given 
 rise to any serious epidemic except in a few cases 
 where its ravages can be traced to recognised 
 carelessness. It is very significant to compare 
 the history of the cholera epidemics of the past 
 few years with those of earlier dates. In the epi- 
 demics of earlier years the cholera swept ruth- 
 lessly through communities without check. In 
 the last few years, although it has repeatedly 
 knocked at the doors of many European cities, it 
 has been commonly confined to isolated cases, 
 except in a few instances where these facts con- 
 cerning the relation to drinking water were ig- 
 nored. 
 
 The study of preventive medicine is yet in its 
 infancy, but it has already accomplished much. 
 It has developed modern systems of sanitation, 
 has guided us in the building of hospitals, given 
 rules for the management of the sick-room which 
 largely prevent contagion from patient to nurse; 
 it has told us what diseases are contagious, and in 
 what way ; it has told us what sources of conta- 
 gion should be suspected and guarded against, 
 and has thus done very much to prevent the
 
 j68 THE STORY OF GERM LIFE. 
 
 spread of disease. Its value is seen in the fact that 
 there has been a constant decrease in the death 
 rate since modern ideas of sanitation began to 
 have any influence, and in the fact that our 
 general epidemics are less severe than in former 
 years, as well as in the fact that more people 
 escape the diseases which were in former times 
 almost universal. 
 
 The study of preventive medicine takes into 
 view several factors, all connected with the 
 method and means of contagion. They are the 
 following : 
 
 The Source of Infectious Material. It has been 
 learned that for most diseases the infectious ma- 
 terial comes from individuals suffering with the 
 disease, and that except in a few cases, like ma- 
 laria, we must always look to individuals suffering 
 from disease for all sources of contagion. It is 
 found that pathogenic bacteria are in all these 
 cases eliminated from the patient in some way, 
 either from the alimentary canal or from skin se- 
 cretions or otherwise, and that any nurse with 
 common sense can have no difficulty in deter- 
 mining in what way the infectious material is 
 eliminated from her patients. When this fact is 
 known and taken into consideration it is a com- 
 paratively easy matter to devise valuable precau- 
 tions against distribution of such material. It is 
 thus of no small importance to remember that the 
 simple presence of bacteria in food or drink is of 
 no significance unless these bacteria have come 
 from some source of disease infection. 
 
 The Method of Distribution. The bacteria must 
 next get from the original source of the disease to 
 the new susceptible individual. Bacteria have no 
 independent powers of distribution unless they
 
 COMBATING PARASITIC BACTERIA. 169 
 
 be immersed in liquids, and therefore their pas- 
 sage from individual to individual must be a pas- 
 sive one. They are readily transferred, however, 
 by a number of different means, and the study of 
 these means is aiding much in checking contagion 
 Study along this line has shown that the means 
 by which bacteria are carried are several. First 
 we may notice food as a distributor. Food may 
 become contaminated by infectious material in 
 many ways; for example, by contact with sewage, 
 or with polluted water, or even with eating uten- 
 sils which have been used by patients. Water is 
 also likely to be contaminated with infectious 
 material, and is a fertile source for distributing 
 typhoid and cholera. Milk may become contam- 
 inated in a variety of ways, and be a source of dis- 
 tributing the bacteria which produce typhoid 
 fever, tuberculosis, diphtheria, scarlet fever, and 
 a few other less common diseases. Again, in- 
 fected clothing, bedding, or eating utensils may 
 be taken from a patient and be used by another 
 individual without proper cleansing. Direct con- 
 tact, or contact with infected animals, furnishes 
 another method. Insects sometimes carry the 
 bacteria from person to person, and in some dis- 
 eases (tuberculosis, and perhaps scarlet fever and 
 smallpox) we must look to the air as a distribu- 
 tor of the infectious material. Knowledge of 
 these facts is helping to account for multitudes 
 of mysterious cases of infection, especially when 
 we combine them with the known sources of con- 
 tagious matter. 
 
 Means of Invasion. Bacteriology has shown us 
 that different species of parasitic bacteria have 
 different means of entering the body, and that 
 each must enter the proper place in order to get
 
 170 THE STORY OF GERM LIFE. 
 
 a foothold. After we learn that typhoid infec- 
 tious material must enter the mouth in order to 
 produce the disease; that tuberculosis may find 
 entrance through the nose in breathing, while 
 types of blood poisoning enter only through 
 wounds or broken skin, we learn at once funda- 
 mental facts as to the proper methods of meeting 
 these dangers. We learn that with some diseases 
 care exercised to prevent the swallowing of infec- 
 tious material is sufficient to prevent contagion, 
 while with others this is entirely insufficient. 
 When all these facts are understood it is almost 
 always perfectly possible to avoid contagion ; and 
 as these facts become more and more widely known 
 direct contagion is sure to become less frequent. 
 
 Above all, it is telling us what becomes of the 
 pathogenic bacteria after being eliminated from 
 the body of the patient; how they may exist for 
 a long time still active ; how they may lurk in 
 filth or water dormant but alive, or how they may 
 even multiply there. Preventive medicine is tell- 
 ing us how to destroy those thus lying in wait for 
 a chance of infection, by discovering disinfect- 
 ants and telling us especially where and when to 
 use them. It has already taught us how to crush 
 out certain forms of epidemics by the proper 
 means of destroying bacteria, and is lessening 
 the dangers from contagious diseases. In short, 
 the study of bacteriology has brought us into a 
 condition where we are no longer helpless in the 
 presence of a raging epidemic. We no longer sit 
 in helpless dismay, as did our ancestors, when an 
 epidemic enters a community, but, knowing their 
 causes and sources, set about at once to remove 
 them. As a result, severe epidemics are becoming 
 comparatively short-lived.
 
 COMBATING PARASITIC BACTERIA. 171 
 
 BACTERIA IN SURGERY. 
 
 In no line of preventive medicine has bacteri- 
 ology been of so much value and so striking in 
 its results as in surgery. Ever since surgery has 
 been practised surgeons have had two difficulties 
 to contend with. The first has been the shock 
 resulting from the operation. This is dependent 
 upon the extent of the operation, and must always 
 be a part of a surgical operation. The second 
 has been secondary effects following the operation. 
 After the operation, even though it was success- 
 ful, there were almost sure to arise secondary 
 complications known as surgical fever, inflamma- 
 tion, blood poisoning, gangrene, etc., which fre- 
 quently resulted fatally. These secondary com- 
 plications were commonly much more serious 
 than the shock of the operation, and it used to be 
 the common occurrence for the patient to recover 
 entirely from the shock, but yield to the fevers 
 which followed. They appeared to be entirely 
 unavoidable, and were indeed regarded as neces- 
 sary parts of the healing of the wound. Too fre- 
 quently it appeared that the greater the care taken 
 with the patient the more likely he was to suffer 
 from some of these troubles. The soldier who 
 was treated on the battlefield and nursed in an 
 improvised field hospital would frequently re- 
 cover, while the soldier who had the fortune to 
 be taken into the regular hospital, where greater 
 care was possible, succumbed to hospital gangrene. 
 All these facts were clearly recognised, but the 
 surgeon, through ignorance of their cause, was 
 helpless in the presence of these inflammatory 
 troubles, and felt it always necessary to take them 
 into consideration.
 
 172 THE STORY OF GERM LIFE. 
 
 The demonstration that putrefaction and de- 
 cay were caused by bacteria, and the early proof 
 that the silkworm disease was produced by a 
 micro-organism, led to the suggestion that the in- 
 flammatory diseases accompanying wounds were 
 similarly caused. There are many striking sim- 
 ilarities between these troubles and putrefaction, 
 and the suggestion was an obvious one. At first, 
 however, and for quite a number of years, it was 
 impossible to demonstrate the theory by finding 
 the distinct species of micro-organisms which pro- 
 duced the troubles. We have already seen that 
 there are several different species of bacteria which 
 are associated with this general class of diseases, 
 but that no specific one has any particular relation 
 to a definite type of inflammation. This fact made 
 discoveries in this connection a slow matter from 
 the microscopical standpoint. But long before 
 this demonstration was finally reached the theory 
 had received practical application in the form of 
 what has developed into antiseptic or aseptic 
 surgery. 
 
 Antiseptic surgery is based simply upon the 
 attempt to prevent the entrance of bacteria into 
 the surgical wound. It is assumed that if these 
 organisms are kept from the wound the healing 
 will take place without the secondary fevers and 
 inflammations which occur if they do get a chance 
 to grow in the wound. The theory met with de- 
 cided opposition at first, but accumulating facts 
 demonstrated its value, and to-day its methods 
 have been adopted everywhere in the civilized 
 world. As the evidence has been accumulating, 
 surgeons have learned many important facts, fore- 
 most among which is a knowledge of the common 
 sources from which the infection of wounds oc-
 
 COMBATING PARASITIC BACTERIA. 173 
 
 curs. At first it was thought that the air was the 
 great source of infection, but the air bacteria have 
 been found to be usually harmless. It has ap- 
 peared that the more common sources are the 
 surgeon's instruments, or his hands, or the cloth- 
 ing or sponges which are allowed to come in con- 
 tact with the wounds. It has also appeared that 
 the bacteria which produce this class of troubles 
 are common species, existing everywhere and uni- 
 versally present around the body, clinging to the 
 clothing or skin, and always on hand to enter the 
 wound if occasion offers. They are always pres- 
 ent, but commonly harmless. They are not for- 
 eign invaders like the more violent pathogenic 
 species, such as those of Asiatic cholera, but may 
 be compared to domestic enemies at hand. It is 
 these ever-present bacteria which the surgeon 
 must guard against. The methods by which he 
 does this need not detain us here. They consist 
 essentially in bacteriological cleanliness. The 
 operation is performed with sterilized instruments 
 under most exacting conditions of cleanliness. 
 
 The result has been a complete revolution in 
 surgery. As the methods have become better 
 understood and more thoroughly adopted, the in- 
 stances of secondary troubles following surgical 
 wounds have become less and less frequent until 
 they have practically disappeared in all simple 
 cases. To-day the surgeon recognises that when 
 inflammatory troubles of this sort follow simple 
 surgical wounds it is a testimony to his careless- 
 ness. The skilful surgeon has learned that with 
 the precautions which he is able to take to-day 
 he has to fear only the direct effect of the shock 
 of the wound and its subsequent direct influence; 
 but secondary surgical fevers, blood poisoning, 
 12
 
 174 THE STORY OF GERM LIFE. 
 
 and surgical gangrene need not be taken into con- 
 sideration at all. Indeed, the modern surgeon 
 hardly knows what surgical gangrene is, and bac- 
 teriologists have had practically no chance to 
 study it. Secondary infections have largely dis- 
 appeared, and the surgeon is concerned simply 
 with the effect of the wound itself, and the power 
 of the body to withstand the shock and subse- 
 quently heal the wound. 
 
 With these secondary troubles no longer to 
 disturb him, the surgeon has become more and 
 more bold. Operations formerly not dreamed of 
 are now performed without hesitation. In former 
 years an operation which opened the abdominal 
 cavity was not thought possible, or at least it was 
 so nearly certain to result fatally that it was re- 
 sorted to only on the last extremity; while to-day 
 such operations are hardly regarded as serious. 
 Even brain surgery is becoming more and more 
 common. Possibly our surgeons are passing too 
 far to the other extreme, and, feeling their power of 
 performing so many operations without inconven- 
 ience or danger, they are using the knife in cases 
 where it would be better to leave Nature to her- 
 self for her own healing. But, be this as it may, 
 it is impossible to estimate the amount of suffer- 
 ing prevented and the number of lives saved by 
 the mastery of the secondary inflammatory trou- 
 bles which used to follow surgical wounds. 
 
 Preventive medicine, then, has for its object 
 the prevention rather than the cure of disease. 
 By showing the causes of disease and telling us 
 where and how they are contracted, it is telling 
 us how they may to a large extent be avoided. 
 Unlike practical medicine, this subject is one 
 which has a direct relation to the general public.
 
 COMBATING PARASITIC BACTERIA. 175 
 
 While it may be best that the knowledge of cura- 
 tive methods be confined largely to the medical 
 profession, it is eminently desirable that a knowl- 
 edge of all the facts bearing upon preventive 
 medicine should be distributed as widely as pos- 
 sible. One person can not satisfactorily apply 
 his knowledge of preventive medicine if his 
 neighbour is ignorant of or careless of the facts. 
 We can not hope to achieve the possibilities lying 
 along this line until there is a very wide distribu- 
 tion of knowledge. Every epidemic that sweeps 
 through our communities is a testimony to the 
 crying need of education in regard to such sim- 
 ple facts as the source of infectious material, the 
 methods of its distribution, and the means of ren- 
 dering it harmless. 
 
 PREVENTION IN INOCULATION. 
 
 It has long been recognised that in most cases 
 recovery from one attack of a contagious disease 
 renders an individual more or less immune against 
 a second attack. It is unusual for an individual 
 to have the same contagious disease twice. This 
 belief is certainly based upon fact, although the 
 immunity thus acquired is subject to wide varia- 
 tions. There are some diseases in which there is 
 little reason for thinking that any immunity is ac- 
 quired, as in the case of tuberculosis, while there 
 are others in which the immunity is very great 
 and very lasting, as in the case of scarlet fever. 
 Moreover, the immunity differs with individuals. 
 While some persons appear to acquire a lasting 
 immunity by recovery from a single attack, others 
 will yield to a second attack very readily. But 
 in spite of this the fact of such acquired immu-
 
 176 THE STORY OF GERM LIFE. 
 
 nity is beyond question. Apparently all infec- 
 tious diseases from which a real recovery takes 
 place are followed by a certain amount of pro- 
 tection from a second attack ; but with some dis- 
 eases the immunity is very fleeting, while with 
 others it is more lasting. Diseases which pro- 
 duce a general infection of the whole system are, 
 as a rule, more likely to give rise to a lasting 
 immunity than those which affect only small 
 parts. Tuberculosis, which, as already noticed, 
 is commonly quite localized in the body, has lit- 
 tle power of conveying immunity, while a disease 
 like scarlet fever, which affects the whole system, 
 conveys a more lasting protection. 
 
 Such immunity has long been known, and in 
 the earlier years was sometimes voluntarily ac- 
 quired ; even to-day we find some individuals 
 making use of the principle. It appears that a 
 mild attack of such diseases produces immunity 
 equally well with a severe attack, and acting 
 upon this fact mothers have not infrequently 
 intentionally exposed their children to certain 
 diseases at seasons when they are mild, in or- 
 der to have the disease " over with " and their 
 children protected in the future. Even the more 
 severe diseases have at times been thus vol- 
 untarily acquired. In China it has sometimes 
 been the custom thus to acquire smallpox. Such 
 methods are decidedly heroic, and of course to be 
 heartily condemned. But the principle that a 
 mild type of the disease conveys protection has 
 been made use of in a more logical and defensible 
 way. 
 
 The first instance of this principle was in vac- 
 cination against smallpox, now practised for more 
 than a century. Cowpox is doubtless closely re-
 
 COMBATING PARASITIC BACTERIA. 177 
 
 lated to smallpox, and an attack of the former 
 conveys a certain amount of protection against 
 the latter. It was easy, therefore, to inoculate 
 man with some of the infectious material from 
 cowpox, and thus give him some protection 
 against the more serious smallpox. This was a 
 purely empirical discovery, and vaccination was 
 practised long before the principle underlying it 
 was understood, and long before the germ nature 
 of disease was recognised. The principle was re- 
 vived again, however, by Pasteur, and this time 
 with a logical thought as to its value. While 
 working upon anthrax among animals, he learned 
 that here, as in other diseases, recovery, when it 
 occurred, conveyed immunity. This led him to 
 ask if it were not possible to devise a method of 
 giving to animals a mild form of the disease and 
 thus protect them from the more severe type. 
 The problem of giving a mild type of this extraor- 
 dinarily severe disease was not an easy one. It 
 could not be done, of course, by inoculating the 
 animals with a small number of the bacteria, for 
 their power of multiplication would soon make 
 them indefinitely numerous. It was necessary 
 in some way to diminish their violence. Pas- 
 teur succeeded in doing this by causing them to 
 grow in culture fluids for a time at a high tem- 
 perature. This treatment diminished their vio- 
 lence so much that they could be inoculated into 
 cattle, where they produced only the mildest type 
 of indisposition, from which the animals speedily 
 recovered. But even this mild type of the dis- 
 ease was triumphantly demonstrated to protect 
 the animals from the most severe form of an- 
 thrax. The discovery was naturally hailed as a 
 most remarkable one, and one which promised
 
 178 THE STORY OF GERM LIFE. 
 
 great things in the future. If it was thus possi- 
 ble, by direct laboratory methods, to find a 
 means of inoculating against a serious disease 
 like anthrax, why could not the same principle be 
 .applied to human diseases ? The enthusiasts be- 
 gan at once to look forward to a time when all 
 diseases should be thus conquered. 
 
 But the principle has not borne the fruit at 
 first expected. There is little doubt that it might 
 be applied to quite a number of human diseases 
 if a serious attempt should be made. But several 
 objections arise against its wide application. In the 
 first place, the inoculation thus necessary is really 
 a serious matter. Even vaccination, as is well 
 known, sometimes, through faulty methods, re- 
 sults fatally, and it is a very serious thing to 
 experiment upon human beings with anything so 
 powerful for ill as pathogenic bacteria. The seri- 
 ousness of the disease smallpox, its extraordinary 
 contagiousness, and the comparatively mild results 
 of vaccination, have made us willing to undergo 
 vaccination at times of epidemics to avoid the 
 somewhat great probability of taking the disease. 
 But mankind is unwilling to undergo such an op- 
 eration, even though mild, for the purpose of 
 avoiding other less severe diseases, or diseases 
 which are less likely to be taken. We are un- 
 willing to be inoculated against mild diseases, 
 or against the more severe ones which are 
 uncommon. For instance, a method has been 
 devised for rendering animals immune against 
 lockjaw, which would probably apply equally 
 well to man. But mankind in general will never 
 adopt it, since the danger from lockjaw is so 
 small. Inoculation must then be reserved for 
 diseases which are so severe and so common, or
 
 COMBATING PARASITIC BACTERIA. 179, 
 
 which occur in periodical epidemics of so great 
 severity, as to make people in general willing to 
 submit to inoculation as a protection. A further 
 objection arises from the fact that the immunity- 
 acquired is not necessarily lasting. The cattle 
 inoculated against anthrax retain their protective- 
 powers for only a few months. How long similar 
 immunity might be retained in other cases we can 
 not say, but plainly this fact would effectually 
 prevent this method of protecting mankind from 
 being used except in special cases. It is out of 
 the question to think of constant and repeated 
 inoculations against various diseases. 
 
 As a result, the principle of inoculation as an 
 aid in preventive medicine has not proved of very 
 much value. The only other human disease in 
 which it has been attempted seriously is Asiatic 
 cholera. This disease in times of epidemics is so- 
 severe and the chance of infection is so great as 
 to justify such inoculation. Several bacteriolo- 
 gists have in the last few years been trying to 
 discover a harmless method of inoculating against 
 this disease. Apparently they have succeeded,, 
 for experiments in India, the home of the chol- 
 era, have been as successful as could be antici- 
 pated. Bacteriological science has now in its 
 possession a means of inoculation against chol- 
 era which is perhaps as efficacious as vaccination 
 is against smallpox. Whether it will ever be used 
 to any extent is doubtful, since, as already pointed 
 out, we are in a position to avoid cholera epidemics 
 by other means. If we can protect our commu- 
 nities by guarding the water supply, it is not 
 likely that the method of inoculation will ever be 
 widely used. 
 
 Another instance of the application of pre-
 
 180 THE STORY OF GERM LIFE. 
 
 ventive inoculation has been made, but one based 
 upon a different principle. Hydrophobia is cer- 
 tainly one of the most horrible of diseases, al- 
 though comparatively rare. Its rarity would ef- 
 fectually prevent mankind from submitting to 
 a general inoculation against it, but its severity 
 would make one who had been exposed to it 
 by the bite of a rabid animal ready to submit 
 to almost any treatment that promised to ward 
 off the disease. In the attempt to discover a 
 means of inoculating against this disease it was 
 necessary, therefore, to find a method that could 
 be applied after the time of exposure i. e., after 
 the individual had been bitten by the rabid ani- 
 mal. Fortunately, the disease has a long period 
 of incubation, and one that has proved long 
 enough for the purpose. A method of inocula- 
 tion against this disease has been devised by Pas- 
 teur, which can be applied after the individual 
 has been bitten by the rabid animal. Apparently, 
 however, this preventive inoculation is dependent 
 upon a different principle from vaccination or in- 
 oculation against anthrax. It does not appear to 
 give rise to a mild form of the disease, thus pro- 
 tecting the individual, but rather to an acquired 
 tolerance of the chemical poisons produced by 
 the disease. It is a well-known physiological fact 
 that the body can become accustomed to tolerate 
 poisons if inured to them by successively larger 
 and larger doses. It is by this power, apparently, 
 that the inoculation against hydrophobia produces 
 its effect. Material containing the hydrophobia 
 poison (taken from the spinal cord of a rabbit 
 dead with the disease) is injected into the indi- 
 vidual after he has been bitten by a rabid animal. 
 The poisonous material in the first injection is
 
 COMBATING PARASITIC BACTERIA. 181 
 
 very weak, but is followed later by a more powerful 
 inoculation. The result is that after a short time 
 the individual has acquired the power of resisting 
 the hydrophobia poisons. Before the incubation 
 period of the original infectious matter from the 
 bite of the rabid animal has passed, the inoculated 
 individual has so thoroughly acquired a tolerance 
 of the poison that he successfully resists the attack 
 of the infection. This method of inoculation thus 
 neutralizes the effects of the disease by anticipat- 
 ing them. 
 
 The method of treatment of hydrophobia met 
 with extraordinarily violent opposition. For sev- 
 eral years it was regarded as a mistake. But the 
 constantly accumulating statistics from the Pas- 
 teur Institute have been so overwhelmingly on 
 one side as to quiet opposition and bring about a 
 general conviction that the method is a success. 
 
 The method of preventive inoculation has not 
 been extensively applied to human diseases in ad- 
 dition to those mentioned. In a few cases a similar 
 method has been used to guard against diphtheria. 
 Among animals, experiment has shown that such 
 methods can quite easily be obtained, and doubt- 
 less the same would be true of mankind if it was 
 thought practical or feasible to apply them. But, 
 for reasons mentioned, this feature of preventive 
 medicine will always remain rather unimportant, 
 and will be confined to a few of the more violent 
 diseases. 
 
 It may be well to raise the question as to why 
 a single attack with recovery conveys immunity. 
 This question is really a part of the one already 
 discussed as to the method by which the body 
 cures disease. We have seen that this is in part 
 due to the development of chemical substances
 
 1 82 THE STORY OF GERM LIFE. 
 
 which either neutralize the poisons or act as 
 germicide upon the bacteria, or both, and perhaps 
 due in part to an active destruction of bacteria 
 by cellular activity (phagocytosis). There is little 
 reason to doubt that it is the same set of activi- 
 ties which renders the animal immune. The forces 
 which drive off the invading bacteria in one case 
 are still present to prevent a second attack of the 
 same species of bacterium. The length of time 
 during which these forces are active and sufficient 
 to cope with any new invaders determines the 
 length of time during which the immunity lasts. 
 Until, therefore, we can answer with more exact- 
 ness just how cure is brought about in case of 
 disease, we shall be unable to explain the method 
 of immunity. 
 
 LIMITS OF PREVENTIVE MEDICINE. 
 
 With all the advance in preventive medicine 
 we can not hope to avoid disease entirely. We 
 are discovering that the sources of disease are on 
 all sides of us, and so omnipresent that to avoid 
 them completely is impossible. If we were to 
 apply to our lives all the safeguards which bac- 
 teriology has taught us should be applied in order 
 to avoid the different diseases, we would surround 
 ourselves with conditions which would make life 
 intolerable. It would be oppressive enough for 
 us to eat no food except when it is hot, to drink 
 no water except when boiled, and to drink no 
 milk except after sterilization ; but these would 
 not satisfy the necessary conditions for avoiding 
 disease. To meet all dangers, we should handle 
 nothing which has not been sterilized, or should 
 follow the handling by immediately sterilizing the
 
 COMBATING PARASITIC BACTERIA. 183; 
 
 hands; we should wear only disinfected clothes; 
 we should never put our fingers in our mouths 
 or touch, our food with them ; we should cease 
 to ride in public conveyances, and, indeed, 
 should cease to breathe common air. Absolute 
 prevention of the chance of infection is impos- 
 sible. The most that preventive medicine can 
 hope for is to point out the most common and 
 prolific sources of infection, and thus enable 
 civilized man to avoid some of his most common 
 troubles. It becomes a question, therefore, where 
 we will best draw the line in the employment of 
 safeguards. Shall we drink none except sterilized 
 milk, and no water unless boiled ? or shall we put 
 these occasional sources of danger in the same 
 category with bicycle and railroad accidents, dan- 
 gers which can be avoided by not using the bicycle 
 or riding on the rail, but in regard to which the 
 remedy is too oppressive for application ? 
 
 Indeed, when viewed in a broad philosophical 
 light it may not be the best course for mankind 
 to shun all dangers. Strength in the organism 
 comes from the use rather than the disuse of our 
 powers. It is certain that the general health and 
 vigour of mankind is to be developed by meeting 
 rather than by shunning dangers. Resistance to 
 disease means bodily vigour, and this is to be de- 
 veloped in mankind by the application of the 
 principle of natural selection. In accordance 
 with this principle, disease will gradually remove 
 the individuals of weak resisting powers, leaving 
 those of greater vigour. Parasitic bacteria are 
 thus a means of preventing the continued life of 
 the weaker members of the community, and so 
 tend to strengthen mankind. By preventive med- 
 icine many a weak individual who would other-
 
 1 84 THE STORY OF GERM LIFE. 
 
 wise succumb earlier in the struggle is enabled to 
 live a few years longer. Whatever be our humani- 
 tarian feeling for the individual, we can not fail 
 to admit that this survival of the weak is of no 
 benefit to the race so far as the development of 
 physical nature is concerned. Indeed, if we were 
 to take into consideration simply the physical 
 nature of man we should be obliged to recom- 
 mend a system such as the ancient Spartans de- 
 veloped, of exposing to death all weakly individ- 
 uals, that only the strong might live to become 
 the fathers of future generations. In this light, 
 of course, parasitic diseases would be an assist- 
 ance rather than a detriment to the human race. 
 Of course such principles will never again be 
 dominant among men, and our conscience tells us 
 to do all we can to help the weak. We shall 
 doubtless do all possible to develop preventive 
 medicine in order to guard the weak against para- 
 sitic organisms. But it is at all events well for us 
 to remember that we can never hope to develop the 
 strength of the human race by shunning evil, but 
 rather by combating it, and the power of the 
 human race to resist the invasions of these or- 
 ganisms will never be developed by the line of 
 action which guards us from attack. Here, as in 
 other directions, the principles of modern humanity 
 have, together with their undoubted favourable 
 influence upon mankind, certain tendencies toward 
 weakness. While we shall still do our utmost to 
 develop preventive medicine in a proper way, it 
 may be well for us to remember these facts when 
 we come to the practical question of determining 
 where to draw the limits of the application of 
 methods for preventing infectious diseases.
 
 COMBATING PARASITIC BACTERIA. 185 
 
 CURATIVE MEDICINE. 
 
 Bacteriology has hitherto contributed less to 
 curative than to preventive medicine. Neverthe- 
 less, its contributions to curative medicine have 
 not been unimportant, and there is promise of 
 much more in the future. It is, of course, unsafe 
 to make predictions for the future, but the accom- 
 plishments of the last few years give much hope 
 as to further results. 
 
 It was at first thought that a knowledge of 
 the specific bacteria which cause a disease would 
 give a ready means of finding specific drugs for 
 the cure of such disease. If a definite species of 
 bacterium causes a disease and we can cultivate 
 the organism in the laboratory, it is easy to find 
 some drugs which will be fatal to its growth, and 
 these same drugs, it would seem, should be valu- 
 able as medicines in these diseases. This hope 
 has, however, proved largely illusive. It is very 
 easy to find some drug which proves fatal to the 
 specific germs while growing in the culture media 
 of the laboratory, but commonly these are of little 
 or no use when applied as medicines. In the first 
 place, such substances are usually very deadly poi- 
 sons. Corrosive sublimate is a substance which 
 destroys all pathogenic germs with great rapidity, 
 but it is a deadly poison, and can not be used as a 
 drug in sufficient quantity to destroy the parasitic 
 bacteria in the body without at the same time 
 producing poisonous effects on the body itself. 
 It is evident that for any drug to be of value in 
 thus destroying bacteria it must have some spe-
 
 1 86 THE STORY OF GERM LIFE. 
 
 cially strong action upon the bacteria. Its germi- 
 cide action on the bacteria should be so strong 
 that a dose which would be fatal or very injurious 
 to them would be too small to have a deleterious 
 influence on the body of the individual. It has 
 not proved an easy task to discover drugs which 
 will have any value as germicides when used in 
 quantities so small as to produce no injurious 
 effect on the body. 
 
 A second difficulty is in getting the drug to 
 produce its effect at the right point. A few 
 diseases, as we have noticed, are produced by 
 bacteria which distribute themselves almost 
 indiscriminately over the body ; but the majority 
 are somewhat definitely localized in special 
 points. Tuberculosis may attack a single gland 
 or a single lobe of the lung. Typhoid germ is 
 localized in the intestines, liver, spleen, etc. 
 Even if it were possible to find some drug which 
 would have a very specific effect upon the tuber- 
 culosis bacillus, it is plain that it would be a very 
 questionable method of procedure to introduce 
 this into the whole system simply that it might 
 have an effect upon a very small isolated gland. 
 Sometimes such a bacterial affection may be local- 
 ized in places where it can be specially treated, as 
 in the case of an attack on a dermal gland, and in 
 these cases some of the germicides have proved to 
 be of much value. Indeed, the use of various dis- 
 infectants connected with abscesses and super- 
 ficial infections has proved of much value. To 
 this extent, in disinfecting wounds and as a local 
 application, the development of our knowledge 
 of disinfectants has given no little aid to curative 
 medicine. 
 
 Very little success, however, has resulted in the
 
 COMBATING PARASITIC BACTERIA. 187 
 
 attempt to find specific drugs for specific diseases, 
 and it is at least doubtful whether many such will 
 ever be found. The nearest approach to it is qui- 
 nine as a specific poison for malarial troubles. 
 Malarious diseases are not, however, produced by 
 bacteria but by a microscopic organism of a very 
 different nature, thought to be an animal rather 
 than a plant. Besides this there has been little 
 or no success in discovering specifics in the form 
 of drugs which can be given as medicines or inocu- 
 lated with the hope of destroying special kinds of 
 pathogenic bacteria without injury to the body. 
 While it is unwise to make predictions as to future 
 discoveries, there seems at present little hope for 
 a development of curative medicine along these 
 lines. 
 
 VIS MEDICATRIX NATURAE. 
 
 The study of bacterial diseases as they pro- 
 gress in the body has emphasized above all things 
 the fact that diseases are eventually cured by a 
 natural rather than by an artificial process. If a 
 pathogenic bacterium succeeds in passing the 
 outer safeguards and entering the body, and if it 
 then succeeds in overcoming the forces of resist- 
 ance which we have already noticed, it will begin 
 to multiply and produce mischief. This multi- 
 plication now goes on for a time unchecked, and 
 there is little reason to expect that we can ever 
 do much toward checking it by means of drugs. 
 But after a little, conditions arise which are hos- 
 tile to the further growth of the parasite. These 
 hostile conditions are produced perhaps in part 
 by the secretions from the bacteria, for bacteria 
 are unable to flourish in a medium containing 
 much of their own secretions. The secretions
 
 1 88 THE STORY OF GERM LIFE. 
 
 which they produce are poisons to them as well 
 as to the individual in which they grow, and 
 after these have become quite abundant the fur- 
 ther growth of the bacterium is checked and 
 finally stopped. Partly, also, must we conclude 
 that these hostile conditions are produced by 
 active vital powers in the body of the individual 
 attacked. The individual, as we have seen, in 
 some cases develops a quantity of some substance 
 which neutralizes the bacterial poisons and thus 
 prevents their having their maximum effect. Thus 
 relieved from the direct effects of the poisons, the 
 resisting powers are recuperated and once more 
 begin to produce a direct destruction of the bac- 
 teria. Possibly the bacteria, being now weakened 
 by the presence of their own products of growth, 
 more readily yield to the resisting forces of the 
 cell life of the body. Possibly the resisting forces 
 are decidedly increased by the reactive effect of 
 the bacteria and their poisons. But, at all events, 
 in cases where recovery from parasitic diseases 
 occurs, the revived powers of resistance finally 
 overcome the bacteria, destroy them or drive 
 them off, and the body recovers. 
 
 All this is, of course, a natural process. The 
 recovery from a disease produced by the invasion 
 of parasitic bacteria depends upon whether the 
 body can resist the bacterial poisons long enough 
 for the recuperation of its resisting powers. If 
 these poisons are very violent and produced rap- 
 idly, death will probably occur before the resisting 
 powers are strong enough to drive off the bacteria. 
 In the case of some diseases the poisons are so 
 violent that this practically always occurs, recov- 
 ery being very exceptional. The poison produced 
 by the tetanus bacillus is of this nature, and recov-
 
 COMBATING PARASITIC BACTERIA. 189 
 
 ery from lockjaw is of the rarest occurrence. But 
 in many other diseases the body is able to with- 
 stand the poison, and later to recover its resisting 
 powers sufficiently to drive off the invaders. In 
 all cases, however, the process is a natural one and 
 dependent upon the vital activity of the body. It 
 is based at the foundation, doubtless, upon the 
 powers of the body cells, either the phagocytes 
 or other active cells. The body has, in short, its 
 own forces for repelling invasions, and upon these 
 forces must we depend for the power to produce 
 recovery. 
 
 It is evident that all these facts give us very 
 little encouragement that we shall ever be able 
 to cure diseases directly by means of drugs to 
 destroy bacteria, but, on the contrary, that we 
 must ever depend upon the resisting powers of 
 the body. They teach us, moreover, along what 
 line we must look for the future development 
 of curative medicine. It is evident that scien- 
 tific medicine must turn its attention toward 
 the strengthening and stimulating of the resist- 
 ing and curative forces of the body. It must 
 be the physician's aim to enable the body to re- 
 sist the poisons as well as possible and to stimu- 
 late it to re-enforce its resistant forces. Drugs 
 have a place in medicine, of course, but this place 
 is chiefly to stimulate the body to react against 
 its invading hosts. They are, as a rule, not spe- 
 cific against definite diseases. We can not hope 
 for much in the way of discovering special medi- 
 cines adapted to special diseases. We must sim- 
 ply look upon them as means which the physician 
 has in hand for stimulating the natural forces of 
 the body, and these may doubtless vary with dif- 
 ferent individual natures. Recognising this, we 
 13
 
 I pO THE STORY OK GERM LIFE. 
 
 can see also the logic of the small dose as com- 
 pared to the large dose. A small dose of a 
 drug may serve as a stimulant for the lagging 
 forces, while a larger dose would directly repress 
 them or produce injurious secondary effects. As 
 soon as we recognise that the aim of medicine is 
 not to destroy the disease but rather to stimulate 
 the resisting forces of the body, the whole logic 
 of therapeutics assumes a new aspect. 
 
 Physicians have understood this, and, espe- 
 cially in recent years, have guided their practice 
 by it. If a moderate dose of quinine will check 
 malaria in a few days, it does not follow that 
 twice the dose will do it in half the time or with 
 twice the certainty. The larger doses of the 
 past, intended to drive out the disease, have been 
 everywhere replaced by smaller doses designed 
 to stimulate the lagging body powers. The mod- 
 ern physician makes no attempt to cure typhqid 
 fever, having long since learned his inability to 
 do this, at least if the fever once gets a foothold ; 
 but he turns his attention to every conceivable 
 means of increasing the body's strength to resist 
 the typhoid poison, confident that if he can thus 
 enable the patient to resist the poisoning effects 
 of the typhotoxine his patient will in the end re- 
 act against the disease and drive off the invading 
 bacteria. The physician's duty is to watch and 
 guard, but he must depend upon the vital powers 
 of his patient to carry on alone the actual battle 
 with the bacterial invaders. 
 
 ANTITOXINES. 
 
 In very recent times, however, our bacteriolo- 
 gists have been pointing out to the world certain
 
 COMBATING PARASITIC BACTERIA. 191 
 
 entirely new means of assisting the body to fight 
 its battles with bacterial diseases. As already 
 noticed, one of the primal forces in the recovery, 
 from some diseases, at least, is the development 
 in the body of a substance which acts as an anti- 
 dote to the bacterial poison. So long as this anti- 
 toxine is not present the poisons produced by the 
 disease will have their full effect to weaken the 
 body and prevent the revival of its resisting 
 powers to drive off the bacteria. Plainly, if it is 
 possible to obtain this antitoxine in quantity and 
 then inoculate it into the body when the toxic 
 poisons are present, we have a means for de- 
 cidedly assisting the body in its efforts to drive 
 off the parasites. Such an antidote to the bac- 
 terial poison would not, indeed, produce a cure, 
 but it would perhaps have the effect of annulling 
 the action of the poisons, and would thus give the 
 body a much greater chance to master the bac- 
 teria. It is upon this principle that is based the 
 use of antitoxines in diphtheria and tetanus. 
 
 It will be clear that to obtain the antitoxine 
 we must depend upon some natural method for 
 its production. We do not know enough of the 
 chemical nature of the antitoxines to manufacture 
 them artificially. Of course we can not deny the 
 possibility of their artificial production, and cer- 
 tain very recent experiments indicate that per- 
 haps they may be made by the agency of elec- 
 tricity. At present, however, we must use natural 
 methods, and the one commonly adopted is sim- 
 ple. Some animal is selected whose blood is 
 harmless to man and that is subject to the dis- 
 ease to be treated. For diphtheria a horse is 
 chosen. This animal is inoculated with small 
 quantities of the diphtheria poison without the
 
 192 THE STORY OF GERM LIFE. 
 
 diphtheria bacillus. This poison is easily ob- 
 tained by causing the diphtheria bacillus to grow 
 in common media in the laboratory for a while, 
 and the toxines develop in quantity ; then, by 
 proper filtration, the bacteria themselves can be 
 removed, leaving a pure solution of the toxic 
 poison. Small quantities of this poison are inocu- 
 lated into the horse at successive intervals. The 
 effect on the horse is the same as if the animal 
 had the disease. Its cells react and produce a 
 considerable quantity of the antitoxine which 
 remains in solution in the blood of the animal. 
 This is not theory, but demonstrated fact. The 
 blood of a horse so treated is found to have the 
 effect of neutralizing the diphtheria poison, al- 
 though the blood of the horse before such treat- 
 ment has no such effect. Thus there is developed 
 in the horse's blood a quantity of the antitoxine, 
 and now it may be used by physicians where 
 needed. If some of this horse's blood, properly 
 treated, be inoculated into the body of a person 
 who is suffering from diphtheria, its effect, pro- 
 vided the theory of antitoxines is true, will be to 
 counteract in part, at least, the poisons which are 
 being produced in the patient by the diphtheria 
 bacillus. This does not cure the disease nor in 
 itself drive off the bacilli, but it does protect the 
 body from the poisons to such an extent as to 
 enable it more readily to assert its own resisting 
 powers. 
 
 This method of using antitoxines as a help in 
 curing disease is very recent, and we can not even 
 guess what may come of it. It has apparently 
 been successfully applied in diphtheria. It has 
 also been used in tetanus with slight success. 
 The same principle has been used in obtaining an
 
 COMBATING PARASITIC BACTERIA. 193 
 
 antidote for the poison of snake bites, since it has 
 appeared that in this kind of poisoning the body 
 will develop an antidote to the poison if it gets a 
 chance. Horses have been treated in the same 
 way as with the diphtheria poison, and in the 
 same way they develop a substance which neu- 
 tralizes the snake poison. Other diseases are 
 being studied to-day with the hope of similar 
 results. How much further the principle will go 
 we can not say, nor can we be very confident that 
 the same principle will apply very widely. The 
 parasitic diseases are so different in nature that 
 we can hardly expect that a method which is satis- 
 factory in meeting one of the diseases will be very 
 likely to be adapted to another. Vaccination has 
 proved of value in smallpox, but is not of use in 
 other human diseases. Inoculation with weak- 
 ened germs has proved of value in anthrax and 
 fowl cholera, but will not apply to all diseases. 
 Each of these parasites must be fought by special 
 methods, and we must not expect that a method 
 that is of value in one case must necessarily be 
 of use elsewhere. Above all, we must remember 
 that the antitoxines do not cure in themselves; 
 they only guard the body from the weakening 
 effects of the poisons until it can cure itself, and, 
 unless the body has resisting powers, the anti- 
 toxine will fail to produce the desired results. 
 
 One further point in the action of the anti- 
 toxines must be noticed. As we have seen, a 
 recovery from an attack of most germ diseases 
 renders the individual for a time immune against 
 a second attack. This applies less, however, to a 
 recovery after the artificial inoculation with anti- 
 toxine than when the individual recovers without 
 such aid. If the individual recovers quite inde-
 
 194 THE STORY OF GERM LIFE. 
 
 pendently of the artificial antitoxine, he does so 
 in part because he has developed the antitoxines 
 for counteracting the poison by his own powers. 
 His cellular activities have, in other words, been 
 for a moment at least turned in the direction of 
 production of antitoxines. It is to be expected, 
 therefore, that after the recovery they will still 
 have this power, and so long as they possess it 
 the individual will have protection from a second 
 attack. When, however, the recovery results from 
 the artificial inoculation of antitoxine the body 
 cells have not actively produced antitoxine. The 
 neutralization of the poisons has been a passive 
 one, and after recovery the body cells are no 
 more engaged in producing antitoxine than be- 
 fore. The antitoxine which was inoculated is 
 soon eliminated by secretion, and the body is 
 left with practically the same liability to attack 
 as before. Its immunity is decidedly fleeting, 
 since it was dependent not upon any activity on 
 the part of the body, but upon an artificial inocu- 
 lation of a material which is rapidly eliminated 
 by secretion. 
 
 CONCLUSION. 
 
 It is hoped that the outline which has been 
 given of the bacterial life of Nature may serve to 
 give some adequate idea of these organisms and 
 correct the erroneous impressions in regard to 
 them which are widely prevalent. It will be seen 
 that, as our friends, bacteria play a vastly more 
 important part in Nature than they do as our 
 enemies. These plants are minute and extraor- 
 dinarily simple, but, nevertheless, there exists a 
 large number of different species. The number
 
 COMBATING PARASITIC BACTERIA. 195 
 
 of described forms already runs far into the hun- 
 dreds, and we do not yet appear to be approach- 
 ing the end of them. They are everywhere in 
 Nature, and their numbers are vast beyond con- 
 ception. Their powers of multiplication are in- 
 conceivable, and their ability to produce profound 
 chemical changes is therefore unlimited. This 
 vast host of living beings thus constitutes a force 
 or series of forces of tremendous significance. 
 Most of the vast multitude we must regard as 
 our friends. Upon them the farmer is dependent 
 for the fertility of his soil and the possibility of 
 continued life in his crops. Upon them the 
 dairyman is dependent for his flavours. Upon 
 them important fermentative industries are de- 
 pendent, and their universal powers come into 
 action upon a commercial scale in many a place 
 where we have little thought of them in past 
 years. We must look upon them as agents ever 
 at work, by means of which the surface of Nature 
 is enabled to remain fresh and green. Their 
 power is fundamental, and their activities are 
 necessary for the continuance of life. A small 
 number of the vast host, a score or two of spe- 
 cies, unfortunately for us, find their most favour- 
 able living place in the human body, and thus 
 become human parasites. By their growth they 
 develop poisons and produce disease. This small 
 class of parasites are then decidedly our enemies. 
 But, taken all together, we must regard the bac- 
 teria as friends and allies. Without them we 
 should not have our epidemics, but without them 
 we should not exist. Without them it might be 
 that some individuals would live a little longer, if 
 indeed we could live at all. It is true that bac- 
 teria, by producing disease, once in a while cause
 
 196 THE STORY OF GERM LIFE. 
 
 the premature death of an individual ; once in a 
 while, indeed, they may sweep off a hundred or a 
 thousand individuals; but it is equally true that 
 without them plant and animal life would be im- 
 possible on the face of the earth.
 
 INDEX. 
 
 Acetic acid, 51. 
 Alcohol, 48. 
 Alexines, 149. 
 Amoeba coh, 165. 
 Animals or plants ? 31. 
 Anthrax, 137, 177. 
 Antitoxmes, 157, 100. 
 Aroma of butter, 76. 
 
 Bacillus acidi lactici, 71. 
 Bacillus, definition of, 33. 
 Bacteria, defined by Hoffman, 15. 
 Beer, bacteria in the manufacture 
 
 of, 50. 
 
 Blood poisoning, 138, 140. 
 Blue milk, 72. 
 
 study of, by Fuchs, 12. 
 
 Bitter milk, 72. 
 Butter making, 75, 78. 
 Butyric acid, 56. 
 
 Canning industry, 64. < 
 Capsule around bacteria, 24. 
 Cheese ripening, 86 ; bacteria in, 
 
 90. 
 
 Cholera Asiatica, 133. 
 Cholera, fowl, 144. 
 
 Classification of bacteria, 33, 36. 
 
 Cleavage products, 41. 
 
 Coal, relation of bacteria to, 123. 
 
 Cocoanut fibre, 44. 
 
 Colony of bacteria, 25. 
 
 Compost heap, 118. 
 
 Cream ripening, 75, 77. 
 
 Curative medicine. 185. 
 Cure of disease by natural processes, 
 187. 
 
 D. 
 
 Dairy industry, 66. 
 Decomposition products, 41. 
 Diphtheria, 134. 
 
 Disease, method of production, 130. 
 Diseases produced by bacteria, 139, 
 
 Distribution of disease germs, 168. 
 Division of bacteria, method of, 18, 
 
 rapidity of, 21. 
 
 Drugs in germ diseases, 185. 
 Dysentery, 165. 
 
 F. 
 
 Farmer's life, relation to bacteria, 
 
 121. 
 
 Fermentative industries, 48. 
 Fermentation, theory of Liebig, 13. 
 Fertilizers, ripening of, 117. 
 Flagella, 29. 
 Flavour of butter, 76 ; of cheese, 
 
 88. 
 
 Food cycle of Nature, 97. 
 Food, relation of bacteria to, 22. 
 
 G. 
 
 Generic names, 37. 
 Green manuring, 120. 
 
 H. 
 
 Habitat of bacteria, 38. 
 
 Hemp, 44. 
 
 Henle, general theory of disease, 12. 
 
 Hydrophobia, 180.
 
 198 
 
 INDEX. 
 
 I. 
 
 Pathogenic bacteria, abundance of, 
 
 Indigo, preparation of, 57. 
 Inflammation in surgery, 153. 
 Internal structure of bactena, 30. 
 Invasion, means of, 145, 169. 
 
 129. 
 Pathogenic bacteria not true para- 
 sites, 131. 
 Phagocytes, 151. 
 Poisons produced by bacteria, 130, 
 
 J- 
 
 132. 
 Preventive inoculation, 175. 
 
 Jute, 44. 
 
 Preventive medicine, 166 ; limits of, 
 
 K. 
 
 182. 
 Products of bacterial life, 41, 47. 
 
 Koch, contribution to bacteriology, 
 
 Pure cultures, 15 ; in vinegar mak- 
 
 16. 
 
 butter making, 82 ; in cheese mak- 
 
 L. 
 
 'ng, 93- 
 Pus, 153 ; pus cocci, 142. 
 
 Lactic acid, 55. 
 
 
 Leather, 46. 
 
 R. 
 
 Leeuwenhoek, studies of, 10. 
 Legumes in nitrogen fixation, 108. 
 Liebig, theory of fermentation, 13. 
 Limits of preventive medicine, 182. 
 
 Recovery from germ diseases, 156. 
 Red milk, 72. 
 Resistance to disease, 147. 
 
 Linen, 42. 
 
 
 Lockjaw, 135. 
 
 S. 
 
 Lysines, 151. 
 
 Sarcina, defined, 19. 
 
 
 Sauer Kraut, 65. 
 
 M. 
 
 Scavengers, bacteria as, 95, 101. _ 
 
 Maceration industries, 42. 
 
 Schwann, studies on fermentation, 
 
 Maceration of skeletons, 46. 
 
 12. 
 
 Malaria, 160. 
 Malignant pustule, 137. 
 Microbe, definition of, 9. 
 Micrococcus, defined, 18. 
 
 Seeds, sprouting of, in. 
 Shape of bactena, 17. 
 Silo, bacteria in, 112. 
 Size of bacteria, 17. 
 
 Milk bacteria, 67, 70. 
 Milk, effect of bacteria on, 70. 
 Milk handling, 74. 
 Mosquitoes and malaria, 164. 
 Motion of bacteria, 28. 
 Muller. studies of, n. 
 Multiplication, rapidity of, 21. 
 Mycoderma aceti, 52. 
 
 Skeletons, 46. 
 Slimy milk, 72. 
 Snuff, preparation of, 59. 
 Soapy milk, 72. 
 Soil, fertility of, 114. 
 Sources of infectious material, 168. 
 Souring of milk, 70. 
 Species, differences between, 23, 34 ; 
 
 N. 
 
 Sponges, 45. 
 
 
 Spores, 25. 
 
 Nitrate beds, 116. 
 Nitrifying bacteria, 103. 
 Nitrogen fixation, 107. 
 Nitrogen loss, 104. 
 
 O. 
 
 Staphylococcus pyogenes, 142. 
 Streptococcus, defined, 19. 
 Streptococcus pyogenes, 142. 
 Surgery, bactena in, 171. 
 Susceptibility of the individual, 145. 
 
 Opium, 63. 
 Oscillaria?, as allies of bacteria, 32. 
 
 T. 
 Tainted milk, 72. 
 
 p 
 
 Tetanus, 135. 
 Tobacco curing, 58. 
 
 Parasitic bacteria, 134. 
 Pasteur, contributions of, 14. 
 
 Troublesome fermentations, 63, 121. 
 Tuberculosis, 136. 
 Typhoid fever, 136.
 
 Vaccination, 176. 
 
 INDEX. 199 
 
 W. 
 
 Wine, bacteria in manufacture of, 
 
 Variation among bacteria, 35. 50. 
 
 Vinegar, 51. Y. 
 
 Virulence of pathogenic germs, 140, I Yellow milk, 72. 
 
 Vis inedicatrix naturae, 187. I Zougloea, 24. 
 
 (16)
 
 000 871 061 8 
 
 VCH 
 
 UN!' CALIFORNIA 
 
 ARY 
 
 LC