Gould's Pocket Pronouncing Medical Dictionary Eij nounced Thin, $2.00, \ Wi Bacilli, and Me both Ei "The ( accuracy nearly e British 2 By GEORGE M. GOULD, A.M., M.D. PO( By Dictiona by R. J. Gilt Ed Eve and tho be given thorough v BIOLOQY LIBRARY G Medical n, Edited I Corners, e a brief lich may d treated BLuuent desiring TX> refresh his rds Pro- 30 Pages. I Corners, , Nerves, , Weights larians in 3 in which to include srature." memory concerning any medical or surgical theme the book will prove invaluable. "In small and convenient size, with the text clearly printed and the subject-matter condensed, this concentrated form of the same author's larger work on medicine and surgery commends itself to the profession for its handiness. The text is well arranged ... the definitions are well written." Detroit Medical Journal. 5-8-22 2KM A Hughes' Practice of Medicine ELEVENTH EDITION REVISED GIVING THE SYNONYMS, DEFINITIONS, CAUSES, SYMPTOMS, PATHOLOGY, DIAGNOSIS, PROGNOSIS, AND TREATMENT OF EACH DISEASE. By DANIEL E. HUGHES, M.D., Late Chief Resident Physician, Philadelphia Hospital; formerly Demonstrator of Clinical Medicine, Jefferson Medical College. Edited by R. J. E. S( OTT, M.A.,B.C.L., M.D., Formerly Attending Physician to the Demilt Dispensary, New York; Editor of Gould and Pyle's Cyclopedia of Medicine and Surgery, etc. 63 Illustrations. 12mo. xix -f 785 Pages. Cloth, $4.25 postpaid. The Treatment is specially full. 406 valuable prescriptions have been included. "This popularity is due to the fact that the book gives practical discussions of diseases as briefly as is consistent with the subject, theories being eliminated." Journal American Medical Association. "This book is intended as a working manual in which the physician may find that which he needs for a rapid restudy of any disease without having to go over the controversial matter usually found in treatises on practice. * * * For case reference and rapid study, there is no better book." Medical Council. "The work is thoroughly modern and is particularly valuable for its discussion of diagnosis and treatment, an immense number of excellent prescriptions being incorporated under the latter head. It is, we believe, unique in including sections on mental diseases and diseases of the skin." New York Medical Journal. The Practitioner's Medical Dictionary - Third Edition, Revised and Enlarged by R. J. E. SCOTT, M.A., B.C.L., M.D., Fellow of New York Academy of Medicine, etc. Many thousands of new medical words are included in this edition. The work contains over 70,000 terms, 962 pages and weighs only 2^ Ibs. Bound in Handsome Flexible Cloth, Marbled Edges, Round Corners, $4.00; with Thumb Index, $4.50. Morris Human Anatomy A Complete Systematic Treatise 6th Edition Revised and Largely Rewritten. With 1164 Illus- trations. Cloth, $10.00.. CONTRIBUTORS Charles R. Bardeen, A.B., M.D., Professor of Anatomy, University of Wisconsin, formerly Associate Professor Johns Hopkins; Eliot R. Clark, A.B., M.D., Professor of Anatomy, University of Missouri, formerly Associate in Anatomy, Johns Hopkins University; Albert C. Eycleshymer, Ph.D., M.D., Professor of Anatomy, University of Illinois; J. F. Gudernatsch, Ph.D., As- sistant Professor of Anatomy, Cornell University Medical College, New York; Irving Hardesty, A.B., Ph.D., Professor of Anatomy, Tulane University of Louisiana; C. M. Jackson, M.S., M.D., the Editor, Professor of Anatomy, University of Minnesota; Dean D. Lewis, M.D., Associate Professor of Surgery in the Rush Medical College, Chicago, Ills.; Richard E. Scammon, Ph.D., Assistant Pro- fessor of Anatomy, University of Minnesota; J. Parsons Schaeffer, Ph.D., M.D., Professor of Anatomy, Jefferson Medrcal College, Phila- delphia; H. D. Senior, M.B., F.R.C.S., Professor of Anatomy, Uni- versity and Bellevue Hospital Medical College, New York; G. Elliot Smith, M.A., M.D., F.R.C.P., F.R.S., Professor of Anatomy, Uni- versity of London; Charles R. Stockard, Ph.D., D.Sc., Professor of Anatomy, Cornell University Medical College, New York; R. J. Terry, A.B., M.D., Professor of Anatomy, Washington University, St. Louis, Mo. A very important feature of any textbook of anatomy is that of the illustrations. They should be very well executed arid clear to give the student a proper notion of the part under discussion. In the new Morris, the illustrations have been carefully selected and prepared. Many of them are printed in colors. This edition in- cludes many new pictures redrawn to supplant the older ones. The drawings are a distinguishing feature of Morris's Anatomy. Microbiology and Microanalyses of Foods 131 Illustrations. 8vo. Cloth, $3.50. By ALBERT SCHNEIDER, M.D., Formerly Microanalyst, U. 8. Bureau of Chemistry. BACTERIOLOGY P ITF I E LD BLAKISTON'S COM PEN DS The Best Series of Manuals for the Use of Students Price of each, Cloth, $2.00 net CSTThese Compends are based on the most popular text-books and the lectures of prominent professors, and are kept constantly revised, so that they may thoroughly represent the present state of the subjects upon which they treat. t^~The authors have had large experience as Quiz- Masters and attaches of colleges, and are well acquainted with the wants of students. GP^They are arranged in the most approved form, thorough and concise, containing over 900 fine illustrations, inserted wherever they could be used to advantage. t^"Can be used by students of any college. t^They contain information nowhere else collected in such a condensed, practical shape. Illustrated Circular Free POTTER'S ANATOMY. Eighth Revised and Enlarged Edition. Including Visceral Anatomy. Can be used with either Morris' or Gray's Anatomy. 139 Illustrations and 16 Plates of Nerves and Arteries, with Explanatory Tables, etc. BRUBAKER. PHYSIOLOGY. Fifteenth Edition, with 26 Illustrations. Enlarged and Revised. LANDIS. OBSTETRICS. Ninth Edition. Revised and Edited by WM. H. WELLS, M. D., Late Associate Professor of Obstetrics, Jefferson Medical College, Philadelphia. 80 Illustrations. POTTER. MATERIA MEDICA, THERAPEUTICS AND PRESCRIPTION WRITING. Eighth Revised Edition. WELLS. GYNECOLOGY. Fourth Edition. With 153 Illustrations. GOULD and PYLE. DISEASES OF THE EYE AND REFRACTION. Including Treatment and Operations and a Section on Local Therapeutics. With Formulae and 109 Illustrations, several of which are in colors. Fourth Edition. LIPSHUTZ. COMPEND OF SURGERY. 185 Illustrations. This volume replaces the Compend of Surgery formerly written by the late Orville Horwitz, M. D. LEFFMANN. CHEMISTRY, Inorganic and Organic. Sixth Edition. Including Urinalysis, Animal Chemistry, Chemistry of Milk, Blood, Tissues, the Secretions, etc. STEWART. PHARMACY. Ninth Edition. Based upon Prof. Remington's Text-book of Pharmacy. ST. CLAIR. MEDICAL LATIN. Second Edition. SCHAMBERG. DISEASES OF THE SKIN. Sixth Edition. Revised and Enlarged. 119 Illustrations. PITFIELD. BACTERIOLOGY. Fourth Edition. 82 Illustrations. HIRSCH. GENITO -URINARY AND VENEREAL DISEASES, AND SYPHILIS. Third Edition. With 59 Illustrations. BJL AKISTCM'S C O NX F K 1SL P S A COMPEND ON BACTERIOLOGY INCLUDING PATHOGENIC PROTOZOA BY ROBERT L. P1TFIELD, M. D. PATHOLOGIST TO THE GERMANTOWN HOSPITAL; LATE DEMONSTRATOR OF BACTERIOLOGY AT THE MEDICO-CHIRURGICAL COLLEGE, PHILA- DELPHIA; VISITING PHYSICIAN TO ST. TIMOTHY'S HOS- PITAL AND CHESTNUT HILL HOSPITAL, PHILA. FOURTH EDITION WITH 4 PLATES AND 82 OTHER ILLUSTRATIONS PHILADELPHIA P. BLAKISTON'S SON & CO 1012 WALNUT STREET v n COPYRIGHT, 1922, BY P. BLAKISTON'S SON & Co. PRINTED IN U. S. A. IY THE MAPLE PRESS YORK PA PREFACE This little book was designed by the writer to serve the needs of the medical student preparing for examination, and for the prac itioner of medicine who desires to acquaint himself with the principle facts of the rapidly growing science of bacteriology. An effort has been made to reduce the subject matter to as concrete a form as possible. While the literature of the subject of immunity is as vast almost as the rest of bacteriology, yet it is hoped that the chapter in this book on immunity gives in outline the essential accepted teachings on the subject. Minute details of cultures and technic are not given. They must be sought for in books on descriptive bacteriology. The author has drawn very freely from many standard text- books. Many illustrations are from Kolle & Wassermann's Atlas, Park and Williams, Williams, McFarland, Tyson's Prac- tice and Abbott. The writer's best thanks are tendered to Dr. Herbert Fox of the University of Pennsylvania (Pepper Laboratory) to whom entire credit is due for the chapters on filterable viruses; the re- arrangement of the chapters, and the new matter that has been added throughout the book. ROBERT L. PITFIELD. 4 8 885 3 TABLE OF CONTENTS CHAPTER I PAGE THE CLASSIFICATION, MORPHOLOGY, AND THE BIOLOGY OF BACTERIA. . . i CHAPTER II PRODUCTS OF BACTERIAL ENERGY 23 CHAPTER III INFECTION 30 CHAPTER IV IMMUNITY 46 CHAPTER V STUDY OF BACTERIA 95 CHAPTER VI BACTERIOLOGICAL LABORATORY TECHNIC 108 CHAPTER VII ANTISEPTICS AND DISINFECTANTS 135 CHAPTER VIII BACTERIA 143 CHAPTER IX ANIMAL PARASITES '. 232 CHAPTER X THE FILTERABLE VIRUSES 255 CHAPTER XI BACTERIOLOGY OF WATER, SOIL, AIR AND MILK 278 INDEX 287 vii COMPEND OF BACTERIOLOGY CHAPTER I THE CLASSIFICATION, MORPHOLOGY, AND THE BIOLOGY OF BACTERIA BACTERIA (fission fungi or schizomycetes) may be defined as very minute unicellular vegetable organisms, almost always devoid of chlorophyll, and generally unbranched, that reproduce themselves asexually by means of direct division or fission, spores, or gonidia. They are allied closely on the one hand to the higher fungi, such as the moulds, and on the other to the algae. Many forms in one phase of development closely resemble members of other groups, and it has always been difficult to classify them. Various botanical classifications have been employed by different bacteriologists. The following one is based somewhat upon Migula's, and that adopted by Lehmann and Neumann, which was compiled from the systems of Flugge, Fischer, Ldffler, and Migula. CLASSIFICATION. Bacteria may be conveniently divided into six families, according to their morphology or shape. I. COCC AC EJE. Spherical or spheroidal bacteria. Globular in free state but usually seen with one axis slightly larger. They do not have parallel sides like the bacilli. To mul- tiply, the cell divides into halves, quarters, or eighths, each of which grow again into perfect spheres. Endospores and flagella are very rare (Lehmann and Neumann). If mobile they are called Planococcus or Planosarcina. 2 . . . BACTERIA (a) Streptococcus. Cells that divic^e in one direction only and grow in chains. (b) Micrococcus. Cells that divide in two directions, or irregularly; with this group staphylococcus may be classed. Also tetrads, which form into fours by division in two directions. (c) Sarcina. Cells that divide in three directions so that bale-like packages, or blocks of eight are formed. At least one variety (Sarcina agilis) is motile, having fla- gella. Plates of cocci, one thick in the plane, are called " merismopedia"" II. BACTERIACE^:. ROD bacteria are straight or slightly curved. Each cell is from two to six times as long as broad. Division takes place in one direction only, and at right angles to the long axis. Spores may be produced or may not. They may have flagella, or may not. (a) Bacterium.- Neumann Have no endospores. Migula no flagella. (b) Bacillus. Neumann Have endospores, and often grow in long threads. Migula Flagella present at any part of cell, peritrichic in arrangement. (c) Pseudomonas. Have endospores very rarely. Flagella only at ends. in. SPIRILLACE^:. -Spiral bacteria. Unicellular, more or less elongated. Twisted more or less like a corkscrew. Cells are sometimes united in short chains. Generally very motile. Spores are known in two varieties only. (a) Spirosoma. Rigidly bent. No flagella. (b) Vibrio or Microspira. Cells that are rigidly bent like a comma, and have always one, occasionally two polar flagella. (c) Spirillum. Are long and spiral, like a corkscrew, are rigid, and have a bunch of polar flagella. CLASSIFICATION 3 (d) Spirochaeta. Cells with long flexible spiral threads, without flagella. Some move by means of an undulating membrane. These have been thought to belong to the bacteria but those that move by an undulating membrane should be. classified with the protozoa. IV. MYCOBACTERIACE^S. Cells as short or long filaments, which are often cylindrical, clavate (club-shaped), cuneate or irregular in outline, and display true or false branching. Spores are not formed, but gonidia are. They have no fla- gella, and division takes place at right angles to the long axis. There is no surrounding sheath as in the next family (V) . (a) Mycobacterium, Cells are short cylindrical rods, some- times wedge-like, bent, or Y-shaped : long and filamentous. They exhibit true branching, and perhaps produce coccoid elements and gonidia, but no flagella. The Corynebac- terium of Lehmann and Neumann belongs to this group. Many are acid-fast. (b) Streptothrix or Actinomyces (ray fungus) are long mycelial threads, that radiate in indian-club, or loop-like forms, with true branching and delicate sheaths, devoid of gonidia and flagella. Growth coherent, mould-like and dry. Often powdery on the surface in culture media, frequently emitting a musty odor. A few species are weakly acid-fast. V. CHLAMYDOBACTERIACE^:. Sheathed bacteria. Cells are characterized by an enveloping sheath about branched and unbranched threads. Division takes place at right angles to the long axis of the cells. (a) Cladothrix are distinguished by false dichotomous branching. Multiplication is affected by separation of whole branches, and by swarm spores or motile gonidia having flagella. 4 BACTERIA (b) Crenothrix. Filaments are fixed to a nutrient base. Are usually thinner at the base than at the apex, formed of unbranched threads that divide in three directions of space, and produce in the end two kinds of gonidia, probably of bisexual nature. (c) Phragmidiothrix. Cells are first united into unbranched threads by means of delicate sheaths, branching threads are then formed. Division takes place in three directions of space, producing sarcina-like groups of gonidia, which, when free, are spherical. (d) Thiothrix. Are unbranched cells, sheathed, without flagella, divided only in one direction^ and contain sulphur granules. VI. BEGGIATOACE^:. Cells united to form threads that are not sheathed: have scarcely visible septa; divide in one direction, and motile only by an undulating membrane, not by flagella. (a) Beggiatoa. Cells containing sulphur granules. Bacteria may furthermore be classified according to their biolog- ical characteristics, which may be wonderfully different. The ulti- mate differentiation of one species from another depends not only on the morphology, which may be precisely similar, but on its bio- logical behavior in culture media and in the tissues of animals un- der identical conditions. Again, different individuals of a given species may vary extraordinarily one from another in form and size, yet the chemical behavior is invariably the same. Hence it is only by observation of the development of bacteria in culture media, and the reactions produced in it, and in the bodies of ex- periment animals, that we can identify them positively from others of a foreign species. No bacteriologist is able by a simple micro- scopical examination of a given bacterium, to identify it absolutely at all times. The higher groups of fungi may be classified conveniently as follows : CLASSIFICATION 5 BLASTOMYCETES-YEASTS. Budding fungi. Character- istic lies in predominant round or elliptical unit; some few form mycelia; division by endospores or budding; important in fer- mentation and in disease. Divided into: Saccharomyces. Endospores and budding, fermenters. No mycelia. Monilia. Budding. No spores mycelia fermenters. Oidia. Budding. No spores mycelia non-fermenters. Coccidioides. Spores. No budding mycelia non-fermen- ters. HYPHOMYCETES-MOULDS. Mycelium-forming fungus; division by spores, branching, budding, or intercalary division; some bisexual. Divided into: Phycomycetes. Mucorinae sometimes bisexual division by grouped spores or segmentation of mycelium. Not important pathologically. Example Mucor. Mycomycetes. Asexual forms dividing by spores in a sac or by end organs sexual forms dividing by specially developed cells. Mycelia predominate. Example Aspergillus. These are the principal groups of yeasts which can be reasonably well classified. There are others, Microsporon, Trichophy ton, and Sporothrix, that have a decided pathogenic importance but for which a systematic position is not easy to give. They belong probably between the two above classes in that mycelial growth with lateral budding and spore formation are their characters. Bacteria that are globular in form are called cocci. Cocci that divide in one direction of space and grow in chains are called streptococci (Fig. i). Cocci that divide irregularly and form parrs of fours, or irregular groups, are called micrococci. Those of this class that form pairs are frequently called diplococci. 1 When they form fours by divi- sion in two directions, they are called tetrads. But when they 1 This word is frequently used as if it were a biological term indicating some species identity, e.g., Diplococcus pneumoniae. There is no biological group called Diplococci and the term should be used in a descriptive sense. The cause of pneumonia is now called Streptococcus pneumoniae. BACTERIA divide irregularly and form masses resembling bunches of grapes, they are spoken of a staphylococci (Fig. 2). Coeci that divide in three directions are called sarcina. One single coccus, by division in three directions, forms cubes of eight FIG. i. Large and very large streptococci. (Kolle and Wassermann.) or more, each of which becomes globular and equal in size to the parent. Motile micrococd are those that divide in two directions of space and have flagella. They are known as planococci. FIG. 2. Staphylococci. Streptococci. Diplococci. Tedrads. Sarcinae. (Williams.) Micrococci that divide in three directions, and are motile, are called planosarcina (Fig. 3). Bacteria that resemble straight rods are called bacilli. These may be short and thick, or long and thread-like; are never curved, but may be slightly bent. CLASSIFICATION Bacilli may grow singly or in chains; may be flagellated; contain spores and gonidia; or, may be devoid of flagella. Members of the spirillaceae that resemble a curved rod, or are FIG. 3. Planosarcina ureae, showing very long flagella. (Kolle and Wassermann.) comma-shaped, are known as vibrios (Fig. 4). Those of the same family that resemble a corkscrew, are called spirilla. When they are like long spiral threads they are called SpirocJUttd (Fig. 5) . Any of these different members of the family of Spirillaceae may grow in chains. In clinical medicine it is common to speak of the streptococcus pneumonia as the pneu- mococcus. As the organism appears in the diseased lung, or in the sputum, one diameter of the coccus is invariably longer than another, and the rule of equal diameters cannot be applied to it. But in culture media, the organism resembles a true coccus, being globular and growing in chains. It is then called the Streptococcus pneumoniae. It is common also to speak of mem- bers of the family of Mycobacteriacea as bacilli, as they are more FIG. 4. Cholera vibrios. (Greene's Medical Diagnosis.) 8 BACTERIA commonly met with in this form in clinical examinations, and in cultures. Hence, we frequently hear of the bacillus of tubercu- losis, and not the Mycobacterium tuberculosis. Among the higher bacteria, the differentiation of those belong- ing to the sheathed group, or Chlamydobacteriacea, is difficult, as it depends largely upon the formation of the false branching and the gonidia. When bacteria exhibit many, or various forms, in the same culture, as does the typhoid bacillus, we speak of FIG. 5. Spirochaeta of relapsing fever. (Kolle and Wassermann.) them as pleomorphic, or as showing pleomorphism. To eluci- date: Man is pleomorphic, because among adult individuals some are tall or short, fat or thin. Involution or Degeneration Forms. When the best or opti- mum conditions for bacterial life (see page 18) are not found, bacteria present appearances quite different from those of the young, active or perfect adult type. These changes are called involutionary if temporary, or degenerative if permanent. For example: the diphtheria bacillus under good conditions for life is a straight or slightly bent rod staining in a granular manner. CLASSIFICATION Q If living under unsuitable conditions it becomes quite short, and stains solidly. Again, bacilli that are accustomed to appear as short elements may grow to long threads without dividing, or swell into unrecognizable form. Branching is sometimes seen in rods and spirals, a condition due in certain cases to involution, in others naturally among the higher bacteria. To measure bacteria, we use the thousandth part of a milli- meter, called the micromillimeter, or micron, as the unit. The Greek letter ju is the symbol for this unit. A micron is about M5>ooo of an inch, yet a bacterium i n long, and % fj. in width, is very large in comparison to some things that scientists measure, such as the thickness of oil films, soap bubbles, or light-wave lengths, in which the unit is a micromicron, and is symbolized by /*/*. The shortest light-wave lengths are about 400 /*/*> or .4 ju, while chromatic threads in cells of bacteria are often 100 w in width. Then again there are many things smaller than these threads. The thinnest part of a bursting soap bubble is but 7 juju in thickness. There are certain infectious agents that are submicroscopic; that is, invisible even by the aid of Siedentopf's ultraviolet microscope, which shows objects smaller by half a light- wave length (.2 AIJU). The structure of the bacterial cell is very simple, consisting of a delicate poorly staining limiting membrane or wall enclosing a mass of substance with strong affinity for basic dyes like methylene blue. Just what part of the bacterial interior is cytoplasm and what is nucleus is not definitely known. Some observers believe that all that is stained is chromatin, or nuclear matter diffusely distributed through the bacterial cell, while others think that a delicate cytoplasm exists under the wall and that it is overshadowed by relatively great proportional bulk of the nucleus. In the course of the rod we often see metachromatic bodies, called the Babes-Ernst granules, and unstained spaces called vacuoles, both of which are common to many bacteria. They 10 BACTERIA may be ingested substances but some are lipoidal or carbohy- drate in nature. These bodies are demonstrated by staining with basic dyes and may be of importance in determining the mycobacteria. It is thought that they play a role in reproduc- tion (Fig. 65). The food of the bacterium passes through the cell wall by osmosis. The cell wall of certain organisms, for example the FIG. 6. Zooglea formation. (Leuconostoc.) (Kolle and Wassermann.) pneumococcus, undergoes a change whereby a mucilaginous or gelatinous capsule is formed outside the cell wall. Its use is not known. The cell wall is generally the first portion of the cell to be attacked by certain specific substances (ferment) found in the blood of immunized animals, called bacteriolysins and agglutinins. Where great masses of bacteria are clumped in excessive mucilaginous material we speak of this condition as zooglea (Fig. 6). We sometimes find, as a prolongation of the cell wall, filament- ous organs of locomotion known as flagella. Bacteria without flagella are sometimes called gymnobacteria, those possessing CLASSIFICATION II them, trichobacteria but these terms are falling into disuse because the latter is now-a-days applied to higher groups that grow in hair like forms. However the following may be described: When they have one flagellum we call them monotrichous bacteria, and amphitrichous when there are two flagella, one at each pole (Fig. 7). When the cell is surrounded by flagella, it is known as a peritrichous bacterium, and lopho- trichous when the flagella are ar- ranged in tufts of two or more. These are simple adjectives and not FIG. 7. Spirillum undula with polar flagella. (Kolle and Wassermann.) FIG. 8. Bacillus proteus vul- garis, showing peritrichous fla- gella. (Kolle and Wassermann.) now used as terms of classification. The tetanus bacillus is an example of a peritrichous organism, while the bacillus of green pus is called monotrichous, because of its single flagellum. Flagella are not pseudopods, but distinct organs of locomo- tion. In certain bacteria of the Beggiatoa, locomotion is accom- plished by a peculiar amoeboid motion, or by an undulating membrane. On looking at bacteria known to have no powers 12 BACTERIA t of voluntary motion, they are seen to oscillate, tremble or move slightly. Suspensions of india-ink in water are seen to do the same thing, as are other inanimate suspensions. This molecular movement is known as the Brownian motion. By ordinary staining methods, and in preparations of living bacteria known to be flagellated, these organs of locomotion cannot be seen, as a rule. Occasionally, however, one may be seen under either condition. Generally, strong solutions of aniline dyes, to which powerful mordants have been added, are necessary to stain the capsule of bacteria and the attached flagella. The motion of bacteria varies from a simple rotatory, on one axis, to a swing- ing, shaking, boring or serpentine action. The location of the flagella has some influence upon the motion they impart. Flagella may be broken off from the cell body by agitation, but when separated may still be clumped by agglutinating sera. Flagella may have other functions than locomotion. It is possible that they serve as organs for the absorption of nour- ishment from the surrounding media. The presence of very long or very numerous flagella does not necessarily presage very active motion. At times, under certain conditions, an organism ordinarily motile and flagellated will appear immobile and non- flagellated (Lehmann and Ziferler), but this is rare. Certain flagella have in their continuity little round granules, or bodies, which apparently have nothing to do with the functions of locomotion but may have something to do with the nutrition of the cell. The test of motility of a bacterium is to see it pro- gress by itself completely across the field of the microscope. REPRODUCTION. The process of direct cell division is the commonest way by which bacteria multiply; hence comes the name of fission fungi. The ways of reproduction of the bacteria high in the scale are by direct division, branching, and by means of spores, and by other granules called gonidia. The spores appearing in the lower bacteria, bacilli for example, are not reproduction forms but states of high resistance. SPORULATION 13 The process of direct or binary division is very simple, and may be a matter of twenty minutes, or as long as six hours. Division is almost always across the cell in the direction of the short axis, though it may in some bacteria be in a direction parallel to the long axis, but this is uncommon. By means of the hanging-drop or the block-culture method, on an inverted cover-glass the process may be observed easily. The phenomena of division begin by an elongation of the cell, soon followed by a constriction of pinching in of the cell on both sides, at an equatorial point. The process begins to be apparent in the cell wall and extends inward. Division may occur in one, two, or three directions, or planes. By cell division bacteria multiply by geometrical progression. One cell at the end of a period becomes two, and at the end of a second period these two become four; at the end of another period these four become eight; after twenty-four hours they may number many millions. It is well that the food supply soon gives out and that the products of bacterial metabolism, such as acids and ferments, inhibit their growth. By this rapid bacterial multiplication, carcasses of animals are disintegrated and the higher nitrogenous compounds are reduced to simple gases that are quickly dissi- pated in the air. SPORULATION. Sporulation is of two kinds: the first and most important for hygiene is that into which some pathogenic bacteria go when they meet unfavorable conditions and it affords protection against all but the most vigorous disinfection; the second kind is a specialized function of the higher bacteria and moulds by which reproduction occurs (vegetative). In the latter case it is not impossible that some sexual specialization occurs. The first mentioned are called Endospores. Vegetative sporulation corresponds to the flowering of the higher plants, and is observed under the most favorable vital conditions. Endospores are produced under stress of circum- BACTERIA stances, when certain agencies or conditions, such as absence of food, drying, and heat, threaten the extinguishment of the organ- ism. Spores are bright, shining, oval, or round bodies, which do PIG. 9. The formation of spores. (After Fischer from Frost and McCampbell.) FIG. 10. Spores and their location in bac- terial cells. (After Frost and McCampbell.) not take aniline dyes readily, and which, when they are stained, retain the color more tenaciously than the adult cells. They resist heat, often withstanding a temperature of i5oC. dry heat for an hour. Steam under pressure at a temperature of i5oC. will invariably kill them after a short exposure. fl 8 FIG. ii. Spore germination, a, direct conversion of a spore into a bacillus without the shedding of a spore-wall (B. leptosporus) ; b, polar germination of Bad. anthracis; c, equatorial germination of B. suUilis; d, same of B. mega- terium; e, same with "horse-shoe" presentation. (After Novy.) Spores are situated either in the ends of the adult organism (polar) or in the middle (equatorial), and the spore is discharged (sporulation) either from the end or through the side. SPORULATION . 15 The spore is developed in the bacterial cell as follows: If the organism is a mobile one it becomes quiet before sporulation, during which the flagella are retained. The position of the spore is early marked by a granularity of the bacterial body at one point, an area soon assuming a clear glistening character, often with a double contour, which may or may not increase the thickness of the cell. If unfavorable conditions continue the cell body disintegrates and disappears leaving the spore bare. ?IG. 12. Capsules. Bad. pneumonia (Friedlander;. (After Weichselbaum from Frost and McCampbell.) Certain spore bearing bacteria grown for a week at 42C. lose the power to form spores; likewise their progeny. As a rule the anthrax bacillus does not form spores in the bodies of animals. Free oxygen is required for sporulation by some bacteria. One spore only is produced by an adult cell. Some forms of bacteria can be differentiated from each other only by the way in which they sporulate, whether from the poles or the equator. Spores are formed chiefly by the rod-shaped bacteria especially the anaerobic and saprophytic organisms and these varieties always have a high thermal death-point. Certain round bodies I 6 . BACTERIA found in bacteria of high thermal death-point, are called by Heuppe arthrospores. It is believed that they are without significance. Arthrospores are common among the micrococci and may be associated with capsule formation and cell enlarge- ment. The whole cell may stain more intensely. They are also to be sought among the Streptothrix genus. Spores resist chemicals for a long period, and withstand drying, even in lime plaster, for years. It is believed that the thick capsule enables them to resist these deleterious agents. FIG. 13. Pest bacilli showing capsules. (Kolle and Wassermann.) Sporulation is more apt to occur under poor nutritive conditions. The anthrax bacillus thrives at i3C. but cannot sporulate below i8C. Anthrax spores have been known to resist the germicidal action of a 5 percent carbolic acid solution for forty days. Capsules. Certain well-known pathogenic bacteria have thick well-marked capsules. The pneumococcus, pneumobacillus, and Bacillus aerogenes capsulatus, are well-known examples of such capsulated organisms. The capsule is not always constant. It often disappears when the organism is grown in culture media (Figs. 12 and 13). THE CHEMICAL COMPOSITION OF BACTERIA 17 The higher bacteria are those from the Mycobacteriacea up to the yeasts and moulds. They are higher than the Bacteriacea because they tend to form truly or falsely branching filaments and specialized segments, gonidia, which may behave as sex organs. Few of them are pathogenic, except in the genera Mycobacterium and Streptothrix. To the former belongs the diphtheria and tubercle bacillus, both of which are said to have branching involution forms, while to the latter belong the organ- isms of actinomycosis and Madura foot. The Chlamydo- bacteriacea and Beggiatoa are Saprophytes. These require special technique for the laboratory culture. The Yeasts or Blastomycetes or budding fungi are next in order. They consist of sharply and doubly outlined, refractive, oval bodies which may grow out into short stalks called mycelia. They grow well in the laboratory and may produce pigments. They are much larger than the bacteria (10-25 /x long). They multi- ply by budding with a separation and removed growth of the young form. They may produce a local or general infection in man, Blastomycosis. They are used in beer making. The commonest genus is Saccharomyces. The Moulds or Uyphomycetes represent the next highest group of the plant algae. They are characterized by a greater promi- nence of the mycelium over simple segments or bodies. They are widespread in nature and many are pathogenic. They multiply by segmentation of the mycelia into gonidia or by the development of special spore masses called sporangia. Fur- ther refinements of the spores into sexual elements is known. They are chiefly of interest to the physician on account of the skin diseases that they occasion. THE CHEMICAL COMPOSITION OF BACTERIA Bodies of bacteria contain water, salts, certain albumins, and bodies that may be extracted with ether. Among the latter are lecithin, cholesterin, and triolein. In acid-fast organisms, fatty 1 8 BACTERIA acids and wax have been found. In others, xanthin bases, cellu- lose, starch, chitin, iron salts, and sulphur grains have been dis- covered. The essential protein of the cell body is highly nitrog- enous and is usually combined with some carbohydrate as a glyconucleo-protein. The salts in the ash are mostly composed of various phosphates. Intracellular toxins in combination with the cytoplasm are found in certain groups of bacteria, e.g., B. typhosus. BIOLOGICAL CONDITIONS Bacteria are arbitrarily classes as parasites, or saprophytes. They may be so dependent upon the tissues of the infected organism as to be a strict parasite and incapable of growth under any other condition (Mycobact. leprce), or they may be capable of life on artifical culture media (tubercle bacillus), or of life in the body, on culture media containing organic matter (influenza bacillus), or in the soil (B. tetani). Saprophytes are bacteria capable of living upon dead organic matter, in soil, in water, in air; they are not parasitic and do not resist the defenses of the living body. Certain biological conditions are essential for the growth of bacteria: water, oxygen, carbon ; nitrogen, and salts are neces- sary. For certain parasitic bacteria, highly complex substances are indispensable: meat albumins, peptones, milk, egg albumin, blood serum, and sugars are the ingredients of various culture media. The chemical reaction of such media is important: it should either 'be faintly acid or faintly alkaline. The greatest number of water bacteria grow in media that are slightly acid, while diphtheria produces its strongest toxins and grows best in alkaline media. Salt-free media is required for a number of pathogenic bacteria, e.g., the gonococcus, B. leprae. All bacteria require for their growth either free oxygen, as in air, or combined oxygen, as in albumin, water, etc. Those that BIOLOGICAL CONDITIONS 1 9 only grow when deprived of free oxygen are known as obligate anaerobes, while those that require the presence of oxygen are called obligate aerobes. Those that grow under either conditions are named facultative anaerobes. Free oxygen is needed for spore formation by certain bacteria. Anaerobes obtain oxygen as they need it by breaking up their foodstuffs. Nutriment is most important for the growth of bacteria, nitrogenous compounds (albumins) particularly being required. Simple aquatic forms of bacteria can live and grow in distilled water. The addition of the various sugars is of advantage in the cultivation of many bacteria, and glycerine for the growth of some members of the Mycobacteriacea. Blood serum or whole blood is required by some pathogenic organisms. The foodstuffs must be in a form that can diffuse through the cell wall. The temperature of the medium in which various bacteria grow is most important. Bacterial growth is possible between oC. and 7oC., some varieties thrive at the one extreme, and others at the other. Psychrophilic bacteria, are those that grow at i5C., with a maximum of 3oC. and a minimum of oC. Water bacteria of the polar seas belong to this group. Mesophilic grow best at 37C. the temperature of the body and thrive from ioC. (minimum) to 45C. (maximum). All pathogenic bacteria belong to this group. Thermophilic (min. temp. 4oC., max. 6o-7oC.) are most prolific at 50-5 5 C. To this class belong bacteria of the soil. All of this class are spore-bearing. Darkness favors bacterial growth. Association of different kinds of bacteria is of some importance in their growth and welfare and when thus associated, they some- times benefit each other. Such combination is called symbiosis. Antibiosis is the condition when one or more of a mixture of organisms suffers by the presence of others, e.g., the destruction of putrefactive germs in the intestinal tract by lactic acid bacilli. 20 BACTERIA Certain anaerobic bacteria grow in the presence of oxygen if other particular varieties of aerobic bacteria are present. Attenuated tetanus bacilli become virulent if cultivated with Bacterium vulgae. Again, complicated chemical changes, as the decomposition of nitrites with the evolution of nitrogen cannot be accomplished by certain bacteria severally, but jointly, this is quickly brought about. Pfeiffer has shown that certain chemical substances (foods, albumins, etc.), attract bacteria (positive chemotaxis) , while other substances, as turpentine, repel them (negative chemotaxis). Oxygen repels anaerobes and is particularly attractive to aerobes. FREE AGENTS PREJUDICIAL TO THE LIFE OF BACTERIA High temperatures are surely germicidal: 6oC. coagulates mycoprotein of bacteria and other common albumins. The degree of temperature at which bacteria are killed is called the thermal death-point. Most vegetative forms die after a short exposure at 6oC., though some require a higher temperature, e.g., tubercle bacillus. Spores resist boiling, often for hours. Spore-bearing bacilli from the soil often survive a temperature of ii5C. moist heat (steam), from thirty to sixty minutes. Bacteria resist dry heat of i75C. from five to ten minutes. Cold inhibits bacteria; destroys some; but is not a safe germi- cidal agent, as typhoid bacilli have been isolated from melted ice in which they had been frozen for months. Ravenel exposed bacteria to the extreme cold of liquid air ( 3i2F.) and found that typhoid bacilli survived an exposure of sixty minutes; diphtheria, thirty minutes, and anthrax spores, three hours; during this exposure, however, many were destroyed. Light is inimical to the life of bacteria, direct sunlight being the most germicidal, as it destroys some, reduces the virulence of AGENTS PREJUDICIAL TO BACTERIAL LITE 21 others, or interferes with the chromogenic properties. Typhoid, cholera, diphtheria, and many other organisms are killed after an hour or two's exposure to bright sunlight. The ultraviolet or actinic rays are the efficient ones. If free oxygen is excluded, the germicidal action is very materially reduced. Sunlight acting on culture media (free oxygen and water being present) produces after ten minutes, peroxide of hydrogen. This action of light on bacteria has been extensively used, notably by Hansen, as a therapeutic measure for the cure of bacterial skin diseases, espe- cially lupus. Diffuse sunlight, electric light, Rcentgen-rays, con- tinuous and alternating currents of electricity, are also more or less germicidal. Antiseptics, such as metallic salts, formalin, carbolic acid, cresol, mineral acids, and essential oils, are powerful germicides; some even in high dilution. According to Koch, absolute alcohol, glycerine, distilled water, and concentrated sodium chloride solution do not affect anthrax spores, even after acting on them for months. Halogen elements (iodine, bromine, chlorine) are the most powerful germicides. Free acids and alkalies must be very strong to act as disin- fectants. Excessive amounts of sugar, salt, glycerine, and the pyroligneous acids act as destroyers, or inhibitors to bacterial growth in foodstuffs. Metals act as lethal agents in the presence of light and water, by forming metallic peroxides, which either destroy the vitality of bacteria or hinder their growth. Silver, zinc, cadmium, bismuth, and copper, have this action. Consequently silver wire and foil, are used in surgery because of their antiseptic action. Metallic fillings in teeth prevent the growth of bacteria that cause caries. Certain cells in the bodies of animals (leucocytes) and some ele- ments of the blood serum, being bactericidal, are a powerful means of internal defense against infection. If the water of the cytoplasm of bacterial cells is dried out, the vitality of the organism suffers. The length of time required for drying varies, anthrax spores resisting the process for over ten 22 BACTERIA years. Ancient methods of preserving foods from putrefying, and which are still in vogue, depend upon the employment of some of these agents, which are prejudicial to bacterial life. Meats are salted, pickled, dried, or smoked. Fruits are dried, pickled, or immersed in strong saccharine solution, in order to preserve them from decay, in every instance, the absence of moisture, the excess of salt, sugar, or vinegar, or the pyroligneous acid from the smok- ing, prevents bacterial growth, and consequently, decay of the foodstuff. The products of bacterial growths often inhibit, or destroy, the cells that made them, as well as other bacteria. B. pyocyaneus and S. cholera, have this property of secreting autolytic ferments. CHAPTER II PRODUCTS OF BACTERIAL ENERGY According to their chemical activities, bacteria are arbitrarily divided into the following classes: Photogens Chromogens Zymogens Saprogens Aero gens Pathogens Photogens are those bacteria of the sea, putrefying flesh, and damp rotten wood, that produce a faint phosphorescence. Chromogens are bacteria that produce colors as they grow, nota- ble among which may be mentioned the Staphylococcus aureus, that are golden in hue; B. pyocyaneus, of a greenish-blue; and B. prodigiosus which appears a brilliant red. Zymogens are the bacteria of fermentation, which is the chemical transformation of carbohydrates by the action of bac- teria, with the evolution of CO2 CO & H. Such bacteria are use- ful in the industries for the production of alcoholic beverages, wine, beer, etc. Through the actions of these organisms grape sugar is converted into alcohol, lactic acid, and acetic acid. C 6 Hi 2 O 6 = 2 C 2 H 6 O + 2 CO 2 glucose 2 alcohol 2 carbonic acid or C 6 Hi 2 O 6 = 2 C 3 H 6 O 6 2 lactic acid or C 6 H 12 6 = 3C 2 H 4 2 2 acetic acid 23 24 PRODUCTS OF BACTERIAL ENERGY From the bodies of ground yeast cells a soluble ferment, Zymase, has been expressed, which causes alcoholic fermentation of cane and grape sugars. This fact proves that fermentation is not necessarily a vital process. The fermentations of bacterial enzymes may give acids, and also aldehydes, ketones, CC>2, CO, H, N, NH 3 , marsh gas and H 2 S. The carbohydrate splitting powers are used in determinative bacteriology. Fermentation and putrefaction are bacterial enzymic processes of indispensible importance to life. Bacteria reduce excrementi- tious matters to their elements and then others build up these elements into conditions favorable for plants. This process affects the cycle of utility of carbon, sulphur and particularly nitrogen in the air and soil. Some soil bacteria can fix nitrogen from the air for the use of plants. Because of the importance of these processes, culture of appropriate bacteria may be spread upon exhausted soil. These are chiefly nitrifying bacteria. Manure contains the denitrifying organisms. Bacterial fermenta- tions produce the flavor of tobacco, opium and butter. Enzyme Production by Bacteria. These products are difficult to define because few have been obtained in an entirely pure state. They may be described as soluble, but non-dialyzable products, precipitable by salts of heavy metals or by alcohol, destroyed by 70 but resisting drying and decomposition. They are restrained by excess of alkali, of acid, and by an accum- mulation of their own products. Ferments of great variety and power are formed by the zymogens, as proteolytic, which dis- solve proteids, such as casein; tryptic, gelatine liquefying; diastase, which converts starch into sugar; invertase, which changes cane sugar into grape sugar; ferments that curde the casein of milk; and it may well be that the activity of pathogenic bacteria in the body is due to ferments of some kind. The hemolytic action of the golden staphylococcus or the tetanus bacillus is thought, by some, to be of enzymic nature. Organized ferments (bacteria, yeasts) differ from the unorganized SAPROGENS AND PATHOGENS 2$ (pepsin, diastase). The latter " exercise solely a hydrolytic action" (Fischer), causing the molecules of insoluble compounds to take up water and to separate into less complex molecules of a different constitution, which are soluble in water. The organized ones act differently. Highly complex molecules are split up, and numerous substances of a totally different character are formed with the evolution of gases and by-products (Fischer). The reason for this is, perhaps, to be found in the supposition that the bacteria abstract oxygen for their own use, and thus cause the atoms to unite into an entirely different substance. According to the above-named investigator, it is not possible to express such chemical changes by a simple equation. Experiments have shown that B. typhosus and pyocyaneus are able to split up olive oil or fat, and produce glycerine and fatty acids, thus making them accessible to fermentation (Fischer). The action of the buttermilk organisms, while usually very complex, may be represented by the following : Ci 2 H 22 On + H 2 O = C 6 H 12 O 6 + C 6 Hi 2 O 6 lactose galactose dextrose C 6 Hi 2 O 6 = 2C 3 H 6 O 3 galactose lactic acid Saprogens produce putrefaction which is the chemical trans- formation of albuminous bodies with the evolution of nitrogen, and of alkaloidal substances, known as ptomaines. Aromatic elements are also produced, such as indol, phenol, kresol, etc. It is therefore obvious that fermentation and putrefaction are separate processes, the former an action upon carbohydrates, the latter a splitting up of proteins. If has been found that when organisms can attack both substances, the sugars and starches are first broken up; this is what is meant when it is stated that carbohydrates have a "sparing action" upon proteins. Pathogens. If the tissues are receptive to bacteria, and if the latter, in any way, injure the tissues, then the invading organism is called pathogenic. Theoretically the tissues of the body are 26 PRODUCTS OF BACTERIAL ENERGY sterile, but as a matter of fact, isolated pathogenic bacteria such as colon and diphtheria bacilli, streptococci, and pneu- mococci, have been found in the tissues and cavities of the body in the absence of pathological evidence of their presence. Sixteen hours after death the blood and tissues teem with bacteria that have wandered in from the intestines. It has been shown that bacteria, even non-motile ones, can migrate through the body during the agonal period. Bacteria may cause disease in the following ways : (a) mechan- ically, a clump of bacteria may plug a capillary; (b) simply over- whelm the tissues and absorb the oxygen (anthrax); (c) they may cause new growths (tubercle) ; or false membranes to form in the larynx causing suffocation (diphtheria); (d) ulceration of heart valves causing cardiac insufficiency; (e) thrombosis in the veins and arteries; (J) pus formation; (g) by generating toxins that cause anaemias, or degeneration of important elements of the nervous system, parenchymatous organs and the walls of the blood-vessels. The tissues of certain animals are receptive for particular bacteria, and the latter are therefore pathogenic to that animal. B. of swine plague is pathogenic to swine, but not to man. B. typhosus is pathogenic for man, but not to swine. As emphasized above, the activities of bacteria are due to the enzymes they produce. In the course of their life, bodies, called toxins, are formed that have the power of producing illness in higher plants and animals. These bodies are similar to the enzymes. Both are produced in minute quantities. Their exact chemistry is not known, and pure toxins, at least, have probably never been isolated. We test for them by animal experiments while the presence of enzymes may be observed upon artificial culture media. Toxins of bacteria are not the only ones formed. Castor bean produces a body classed among the toxins as does the rattlesnake in its venom. These bodies differ from ptomaines, also poisons, by being less resistant to heat, in causing a peculiar TOXINS 27 blood reaction and by refusing isolation. The toxins are not essential to the life of pathogenic bacteria and some of the usually virulent organisms may grow without toxin development. Toxin productions may be lost and regained. The real object of the toxins is not known, as it is not thought that bacteria gain any- thing by producing disease. They are separate from the other chemical bacterial products. Toxins may be divided into those which are secreted through the bacterial cell wall and diffuse through the median in which organisms are growing, the extra- cellular or soluble toxins, and those which remain within the bacterial cells and are only liberated upon their death and dis- integration, the endotoxins. Closely related to the second class are the so-called toxic bacterial proteins or plasmins. These do not separate from the structures since bacteria which produce them furnish a toxic mass if thoroughly washed, ground and rewashed. Examples and Characters. Soluble or Extracellular Toxins. The best examples are those of the tetanus and diphtheria bacilli. In diseases caused by these germs, bacteria do not enter the body i fluids but the general manifestations are due to absorbed soluble I poisons. Such toxins are soluble in water; they are rendered inert i by heating, sunlight and some chemicals. They dialyze very i slowly and are not crystallizable. They may be precipitated with j the albumen fraction of the medium. They may be precipitated and dried, in which state they keep much longer than when in solution, and then are more resistant to heat. Curiously enough I the toxins may be destroyed by proteoly tic enzymes. Some toxins ! are complex; the tetanus toxin for example, contains two elements, ; one a dissolving power on red blood cells, the other a stimulator i of the motor system. They are specific for each organism. Endotoxins. These are exemplified by the poisons of the ty- phoid and plague organisms. We know little of their chemistry but we may assume that it is of protein material and similar to that of the bacterial cell. These toxins are less rigidly specific 28 PRODUCTS OF BACTERIAL ENERGY than the extracellular poisons. They are probably quite complex in activity as they give rise to various anti-poisons when in the animal body. These poisons are resistant to heating at 8oC. and keep under artifical conditions much longer than soluble toxins. The toxic bacterial proteins are best exemplified by tuberculin. This is complex mixture of the proximal principles of the tubercle bacillus and is probably albuminose in character. These sub- stances are almost as specific for their own germs as the toxins and much more so than the endotoxins. They are capable of produc- ing a reaction in animals similar to that which might be produced by the organisms themselves. For example tuberculin, wholly free from tubercle bacilli, will produce a reddening of the skin or a rise of temperature if injected into a tuberculous individual. The dead tubercle bacillary mass if placed beneath the skin of a healthy guinea pig will set up a local limited miliary tubercle. The reactions from mallein and luetin (q.v.) injection are due to toxic proteins. The proteins are usually thermostable, that is not destroyed at iooC.; this is also called coctostabile. In practice it may not be so simple to separate bacteria that produce the various poisonous elements as the above descriptions would indicate. Toxins are all in a sense specific, that is they are for the most part selective in action, and are harmless if swallowed. The diphtheria toxin is absorbed from a raw inflamed surface under cover of an exudate composed of fibrin and bacteria. The tetanus toxin is absorbed from its seal of manufacture in the depths of a punctured wound. The endotoxin of typhoid bacilli has no pathogenic effect if swallowed or rubbed in skin or mucous membrane. If it be injected under the skin in the absence of bacteria it will call forth reactions on the part of the body similar to those expressed when living typhoid germs are circulating. Toxins are again relative in their affinities. Tetanus toxin is fatal for man and horses while rats and birds are resistant to it. We use this expression of specificity for determining the nature of certain germs. We may speak of failures to react as failures TOXINS 29 of receptivity on the part both of the microbe and the injected animal. Other characters of toxins are that they act in dilute suspen- sions, are destroyed by heat, and produce, when injected in small doses into animals, a specific anti-substance. CHAPTER III INFECTION Infection means the successful invasion of the tissues of the body by either animal (protozoa, vermes) or vegetable (bacteria and moulds) organisms with the evidences of their action. To successfully infect the body, bacteria must enter the tissues, be of sufficient number, find the tissues receptive, and continue to multiply. The skin, mucous membranes, and the various cavities of the body connected with the outside air, teem with countless bacteria at all times, many of which are pathogenic, yet there is no infec- tion, because the tissues are not invaded. Again, there can be no doubt that highly pathogenic bacteria enter the tissues of healthy people at times, in small numbers, and yet no disease is produced, because of their scarcity, or by reason of the tissues not being receptive. Infection implies not only invasion of the body, but injury to the tissue. Certain bacteria may invade a body, and yet create no harm. These bacteria may enter dead or dying body tissues, and secrete poisonous substances (toxins) which may be absorbed, and produce pathologic symptoms known as Saprcemia. Clots of blood in the parturient uterus, and gan- grenous limbs may be invaded by strict saprophytes incapable of life in living tissues, and yet cause much harm by the absorption of their products. Infestation is when organisms, even pathogenic, are present in a place without exciting a reaction; the term is best used however to imply the presence and action of animal parasites. Matter carrying pathogenic germs is called infective. 30 Depending upon the ability to grow in the body, bacteria may be divided into: (i) purely saprophytic ; (2) occasionally para- sitic;