SB TL fl33 LTURAL ;TERIOLOQY 3ELL & HASTINGS 3 Arie. in Lib. LIBRARY OF THE UNIVERSITY OF CALIFORNIA. Class BIOLOGY LIBRARY 6 AGRICULTURAL BACTERIOLOGY BY H. L. RUSSELL DEAN OP THE COLLEGE OF AGRICULTURE UNIVERSITY OF WISCONSIN AND E. G. HASTINGS ASSOCIATE PROFESSOR OF AGRICULTURAL BACTERIOLOGY UNIVERSITY OF WISCONSIN OF THE UNIVERSITY OF MADISON, WISCONSIN H. L. RUSSELL 1909 BIOLOGY LIBRARY G Afffe. Dept. COPYRIGHT, 1909 BY H. L. RUSSELL AND E. G. HASTINGS. STATE JOyRN"AL PRINTING COMPANY PaiNTERS AND STEREOTYPERS MADISON, Wis. FOREWORD. No single line of discovery has exerted a more pro- found influence on the scientific thought of the last few decades than has the development of bacteriology. The researches of Pasteur, Koch, and their successors, opened a field of inquiry that has not only revolutionized all of the biological sciences, but also the applied lines of thought. Medicine was the first of these sciences to re- ceive the impetus from such discoveries, but it is no less true that they exert an equally profound effect on agri- cultural sciences. Too long has agriculture been consid- ered simply an art a vocation which one had to learn wholly in the school of experience, but the serious student of farm life finds it necessary to understand the phenom- ena of the plant and animal world and to combat or util- ize successfully the activities of various microscopic or- ganisms. It is therefore essential, even in a practical course, that this important subject be properly consid- ered. The text here presented deals with the subject briefly, but it is designed to give a comprehensive treat- ment of the different relations which the bacteria bear to problems of farm life. At best, it can only serve to stimulate the interest of the student to pursue this sub- ject more in detail as opportunity permits. 201935 OF TH UNIVERSITY OF CONTENTS SECTION I GENERAL BACTERIOLOGY CHAPTER I Structure, Growth, and Distribution of Bacteria. 1 II Artificial Cultivation of Bacteria 15 SECTION II RELATION OP BACTERIA TO MILK AND OTHER DAIRY PRODUCTS CHAPTEK III Contamination of Milk 22 IV Preservation of Milk 44 V Fermentations of Milk 53 VI Relation of Bacteria to Butter 65 VII Relation of Bacteria to Cheese 73 VIII Relation of Bacteria to Market Milk 82 SECTION III RELATION OF BACTERIA TO DISEASE CHAPTER IX Transmissible Diseases 92 X Anthrax, Black Leg, Hemorrhagic Septicaemia, and Corn Stalk Disease 98 XI Tuberculosis . 110 XII Glanders and Tetanus 127 XIII Rabies , 134 XIV Actinomycosis, Garget, Cow Pox, and Contagi- ous Garget 142 XV Diseases of Hogs 151 XVI Diseases of Fowls 157 XVII Miscellaneous Diseases 161 XVIII Disinfection.. . 165 VI Contents. SECTION IV RELATION OF BACTERIA TO SOILS CHAPTER XIX Relation of Bacteria to Fertility 171 XX Effect of Bacteria on Minerals of the Soil 183 XXI Ammonification, Nitrification, and Denitrifi- cation 186 XXII Fixation of Nitrogen 195 XXIII Bacteria in Manures ^ . . . 207 XXIV Water Supply and Sewage Disposal 214 SECTION V FOOD PRESERVATION AND DISEASES OF PLANTS CHAPTER XXV Preservation of Foods 225 XXVI Diseases of Plants 235 SECTION 1. GENERAL BACTERIOLOGY. CHAPTER I. STRUCTURE, GROWTH AND DISTRIBUTION. Nature of the bacteria. The bacteria belong to the group of plants known as fungi. The fungus plants do not contain the green coloring matter found in ordinary plants. They live on dead or living animal or vegetable matter. Many of the fungi are well known to the farmer and are of great economic importance causing, as they do, such plant diseases as the rusts, smuts and mildews. Other examples of fungi are the various kinds of molds, toadstools and mushrooms. These are more familiar as they are large enough to be seen by the unaided eye, while many other kinds of fungi and es- pecially the bacteria are unfamiliar objects because by the unaided eye an individual plant can not be seen. When massed together in large numbers they become visible but such groupings are rarely found in nature. While the bacteria, themselves, are not familiar ob- jects the effect they produce is very evident in the sour- ing of milk, the spoiling of meat and eggs, the produc- tion of diseases in plants and animals, and in many other ways which are not so readily recognized. Knowledge relating to the bacteria has nearly all been gained within the last thirty years although the bacteria were first seen by a Dutch lens-maker, Antoni van Leeuwenhoek, in 1675. For nearly two hundred years after they were first discovered but little of im- portance was learned concerning them. 2 Agricultural Bacteriology. Structure of bacteria. Plants and animals are made up of cells which are tiny masses of semi-liquid matter surrounded by a membrane, the cell wall. Many kinds of cells are found in each individual higher plant or animal. The sum total of the activities of all the cells constitutes the life of the individual. Bacteria are made of cells the same as other living things, but in- stead of a number of cells being required to form an individual, each cell is a complete organism in itself, capable of carrying on all the processes necessary for the continuance of its life. The single cell can breathe, take in food, live, and reproduce itself. Thus while the bacteria are very simple as to their structure, they per- form all the necessary functions of a living organism. A B C ;. FIG. 1. FORMS OF BACTERIA. A, coccus; B, bacillus; C, spirillum. (After Novy.) Forms of bacteria. Where the individual is reduced to the limits of a single cell, it is evident that not much variation in form is possible. While slight variations in size and shape are to be noted, nearly all the bacteria may be grouped under three general types. The ball- shaped are known as cocci (singular coccus) ; the rod- shaped are called bacilli (singular bacillus) ; if the rods instead of being straight are more or less curved, they are known as spirilla (singular spirillum). The ball- shaped and the rod-shaped are by far the most abun- dant and are the forms of most interest to the student of agricultural bacteriology. Structure, Growth and Distribution. 3 Size of bacteria. All of the bacteria are so small they n not be seen by the unaided eye. In fact their min- uteness is such as to render difficult any adequate con- ception of their size. In a single teaspoonful of sour cream ready for the churn, there are often 1,500.000,000 bacteria. The teaspoonful of cream is not more crowded than is our world with the 1,500,000,000 peo- ple living on its surface. In the drop of cream each organism is living its own life and doing a certain amount of work as is each person on the surface of the globe. The different kinds of bacteria vary considerably in relative size. The largest may be several hundred times as large as the smallest forms. Even with the largest, one hundred or more laid side by side would not equal in thickness an ordinary sheet of paper. Manner of reproduction. Most of the ordinary plants increase in number by forming seeds. The seed ger- minates and grows into a plant which may produce thousands of seeds similar to the one planted. Many kinds of fungus plants reproduce by the formation of spores, which in some ways are analogous to the seeds of the higher plants. The cloud of smoke from the ripe puffball is made up of its tiny spores. The ripe smut on the corn owes its black color to the multitude of spores it contains. In their manner of reproduction the bacteria are to be compared to the individual cell of the higher plant or animal rather than to the entire plant. The germi nating corn plant is made up of a number of cells. These divide each into two, these two cells again divide to form four cells and so on, the plant, meanwhile, in- 4 Agricultural Bacteriology. creasing in size. The bacteria increase in number in a similar way, each cell dividing into two at each division. The mother cell disappears and two daughter cells are FIG. 2. DIVISION OF BACTERIA. The bacteria increase in numbers through the divi- sion of each cell into two cells. (After Novy.) formed, which in turn soon become mother cells and thus the process is repeated. Arrangement of cells. Each kind of plant can be rec- ognized because the cells forming it are arranged in a certain definite way, different from the arrangement of the cells in all other plants. The arrangement of the cells of those kinds of bacteria that cling together after the cell has divided often enables the experienced bac- A B c FIG,. 3. ARRANGEMENT OF BACTERIA. A, streptococci; B, sarcina; C, staphylococci. (After Novy.) teriologist to recognize different types. The cells may be arranged in long or short chains. Such aggregates of cocci are known as streptococci ; clusters of cocci re- sembling bunches of grapes are called staphylococci. Still other forms of cocci divide in such a manner as Structure, Growth and Distribution. 5 to form packets of cells resembling a bale of binder twine (sarcina), while many forms show no regularity in the grouping of the cells. But few of the bacilli and spirilla show a characteristic grouping of the cells. Spores of bacteria. The seeds of plants are not so easily injured by heat, cold, or drying as are the grow- ing plants which bear them. The seeds thus carry over the plant from one growing season to the next. Many kinds of bacteria form within the cell a tiny structure, called a spore, which is much more resistant than the vegetating cell, and hence, in this respect is comparable FIG. 4. SPOKE FORMATION AND GERMINATION. Figures on upper line show various stages of spore development. Lower left hand figure represents the cell issuing from the spore case. to the seeds of ordinary plants. The spores are, how- ever, much more resistant than the seeds of any of the higher plants. Boiling for hours will not kill some kinds of bacterial spores. They can be dried for years and still grow quickly when placed in a favorable food- material. Thus, the bacteria forming spores are able to withstand unfavorable environmental conditions. The spores are unlike seeds in that spore formation is not to be considered as a manner of increasing in 6 Agricultural Bacteriology. numbers since one cell forms but a single spore, and c germination this spore grows into a single cell. N< all bacteria form spores, a very fortunate circumstan< as will be seen later. The resistant spores often gr\ to the dairyman and farmer a great amount of trouble Movement of bacteria. Plants as a rule do not mov yet some of our common plants can move their leave as the ordinary sensitive plant. Many water plan possess organs of locomotion. Certain of the bacter: are able to move in the liquids in which they exis This motion is accomplished by the lashing to and fi of the fine hair-like processes known as cilia. Tl movement of the bacteria is really very slow althoug: when a drop of a liquid containing motile bacteria seen under the microscope, the bacteria seem to be mo 1 ing rapidly about, for their motion is magnified in tl same manner as are the bacteria themselves. Food supply of bacteria. The green plant lives o certain inorganic substances in the soil. The colorle? group of plants to which the bacteria belong, the fung live on living or on dead animal and vegetable matte By far the majority of the bacteria find most favorab] conditions for growth on dead organic matter. The cause the spoiling of our food-stuffs and are largely r( sponsible for the complete disappearance of the aninu and vegetable matter that reaches the soil. They ar thus of the utmost importance for without them th earth would soon be encumbered with the dead bodie of plants and animals. To consume this organic ma1 ter is the function of the class of bacteria known as th saprophytic bacteria. The bacteria that, under natura conditions, live only in the bodies of living plants an* Structure, Growth and Distribution. 1 animals are called parasitic bacteria. To the latter group belong those especially important forms, the pa- thogenic bacteria, which produce the transmissible dis- eases of plants and animals. Some species ordinarily lead a saprophytic life in the soil, but may, if accident introduces them into the bodies of animals, grow and produce serious trouble. These forms are not to be looked upon as parasites since their natural habitat is- not the body of a living animal. The saprophytic as also the parasitic bacteria vary widely as to the kind of food best adapted to their dif- ferent needs. Some kinds of parasitic bacteria grow only in the body of man, others only in certain animals; while still other types grow in the bodies of a large number of different kinds of animals. Some of the soil bacteria grow only on certain kinds of food substances, while others flourish on the widest variety of materials. Condition of the food. Since the food must be ab- sorbed by the bacterial cell before it can be used, it is necessary that it be in solution. Some forms of bac- teria are able to develop digesting substances, known as. enzymes, by means of which they render insoluble ma- terial soluble, utilizing the same in part as food. Bacteria can not, as a rule, grow well in acid sub- stances, a fact which is widely applied in the preserva- tion of human and animal foods. In this respect they differ from most of the fungi which thrive preferably on acid rather than on neutral or alkaline substances. Jellies and plant juices, therefore, spoil from mold de- velopment while blood and animal products as broths and soups undergo bacterial decomposition. Oxygen supply of bacteria. Every living thing, even every living cell of the growing plant or animal, must 8 Agricultural Bacteriology. have air, or rather oxygen. The bacteria are no excep- tion to this rule. Many forms known as aerdbes (liv- ing in the air) can grow only in the presence of oxygen. A smaller group known as anaerobes (living without air) grow only in the total absence of free oxygen. These forms must, however, have oxygen, but their only available source is the combined oxygen which they se- FIG. 5. PHOTOMICROGRAPH OF ANTHRAX BACILLI. The chain-like arrangement is characteristic of this organism. Each member of the chain is an indi- vidual bacillus. Magnified 1,000 diameters. cure from organic substances like sugar. An interme- diate type is able to live and grow under either condi- tion, i. e., in the presence or absence of free oxygen /These are called facultative anaerobes. Moisture supply of bacteria. No cell growth of any kind can take place without moisture. Bacterial changes go on most rapidly in the presence of an abun- Structure, Growth and Distribution. 9 dant supply of moisture. Foods, such as meats, fruits, vegetables and also fodders are protected from the ac- tion of bacteria and molds by drying. Molds require much less moisture for their growth than do the bac- teria. Temperature for the growth of bacteria. In common with other forms of plant life, bacterial growth occurs throughout a relatively wide temperature zone ; in fact, wider than in the case of most other plant forms. Most forms of bacteria are checked in their growth when the temperature approximates 40-45 F. although a few of them thrive near the freezing point. At ordinary air temperatures, multiplication of the cells proceeds apace as is shown by the decomposition of organic substances. During hot summer weather, 80-100 F., decomposi- tion is still further hastened. If, however, the tem- perature is increased much above the blood heat, growth of most forms is checked. A temperature of 180-140 F. actually kills most of the vegetating bac- teria. To exceed this fatal point, known as the ther- mal death point, is the basis of all methods of preserva- tion of foods by heat. Bate of growth of bacteria. When a suitable food is available and temperature conditions are favorable, the bacteria increase in numbers very rapidly. A single organism will divide, and the two daughter cells grow to maturity, ready to divide again, in twenty minutes or less. This rate of growth rarely takes place under na- tural conditions and is never maintained for any con- siderable length of time for most forms of life encoun- ter conditions in nature that restrict their development. 10 Agricultural Bacteriology. Food is not always abundant, the temperature may be- such as to limit or even stop growth. Every living thing has its enemies. These limitations check bacterial growth in the same manner as all the higher forms of life are checked. Under artificial conditions the bacteria may grow very rapidly for a time. For instance, it has been shown that a single organism when placed under the most favorable conditions as to food and temperature will increase in ten hours to the enormous number of 1,240,000,000. This rapid growth does not continue, but, on the other hand, goes on more and more slowly and at last ceases altogether, because the products formed by the organisms] themselves accumulate and make further growth impossible. Every form of life living on plant or animal matter may be killed by its own excretions unless they are removed. The bacteria are no exception to this rule. Effect of cold on bacteria. Low temperatures retard the rate of growth of the bacteria. The exact point at which growth ceases varies widely with different spe- cies. Some forms as the organism causing tuberculosis will not grow below 90 F. Still others will grow at temperatures below freezing when they are present in a liquid like brine that does not freeze. When the sub- stance in which the bacteria are present becomes solid by freezing, growth must cease but the bacteria are not necessarily killed. For example water bacteria are not all killed by freezing although it is popularly supposed that water purifies itself in this manner. Even disease- producing bacteria may resist this degree of cold for a Sfriiclur< . Growth and Distribution. 11 number of months. For this reason ice used in cooling drinking water should come only from uncontami- nated sources. Effect of heat on bacteria. All forms of life are de- stroyed by high temperatures. The seeds of the higher plants are not so easily killed by heat as are the plants themselves and in the same way the spores formed by certain of the bacteria are very difficult to kill. Some must be subjected to the temperature of boiling water (212 F.) for hours in order to destroy them. Two forms of heat are used to destroy bacteria, moist heat, as steam or hot water, and dry heat as produced in an oven. As every one knows, one can place his hand in an oven heated much above 212 F. without in- jury, but the same exposure to steam or boiling water would result in a serious burn. The effect on the bac- teria is the same. For this reason when it is desired to destroy germ life on or in any substance, moist heat is preferably used if it will not injure the object. Effect of light on bacteria. All the plants which con- tain the green coloring matter, chlorophyll, can produce a normal growth only in the presence of light. Fungi grow rapidly in the dark. To some of the fungi the light is not especially injurious. The bacteria, espe- cially the pathogenic bacteria, even in a spore stage, are easily killed by direct sunlight. As previously stated, the spores are very difficult to kill by heating, much more so than the vegetating cell, but sunlight kills the spores of most forms almost as quickly as it- does the growing cell. While the direct sunlight is very efficient in destroy- ing both cells and spores, the diffused light of an ordi- 12 Agricultural Bacteriology. nary house or barn has but little effect. Where the "bacteria are covered by dust or dirt light has no effect. Effect of chemicals on bacteria. Many chemical sub- stances are poisonous to plants and animals. When such substances exert a peculiarly marked effect on germ life they are known as disinfectants or germicides. Corrosive sublimate, carbolic acid, and formaldehyde are the best known and strongest disinfectants. When present in very small amounts they do not kill the bac- terial cells but may prevent their growth. Some chem- icals, even in strong solutions, are not poisonous enough to kill the bacteria but may merely check the growth. Such are known as antiseptics or preservatives. All dis- infectants in a dilute form have an antiseptic action, but not all antiseptics, even in concentrated solutions, are disinfectants. For example, lime is an antiseptic, since it dissolves in water to such an extent as to pre- vent all growth of bacteria, but it does not kill many forms of bacteria. Acids, such as vinegar, are anti- septics, and are constantly used in the preservation of human and animal foods. Products formed by bacteria. When the bacteria grow in any food-substance, parts of the same are con- mimed. As a result of this growth, the bacteria give off from their bodies various kinds of by-products that are very different from the original food-substance. The changes that take place in any substance in which the bacteria are growing are collectively known as il fer- mentations. " Many kinds of by-products are formed "by the various forms of bacteria, such as the acids pro- duced in the souring of milk, and in the change of cider to vinegar, also in the "working" of canned fruits and Structure, Growth and Distribution. 13 vegetables. Alkalies, as ammonia, may be produced as. in the fermentation of urine in the horse stable. Highly poisonous substances are sometimes formed in the bodies of animals by the disease-producing bacteria. Distribution of bacteria. Bacteria are more univer- sally distributed than any other form of life. They be- come very abundant where conditions for growth are suitable, particularly where a fitting supply of food i fcund. The soil is teeming with germ life, for the dead tissues of both plant and animal life find their way to the soil. As most of this material is found in the upper part of the soil, the bacteria are naturally more abund- ant here than in the subsoil. Some of the kinds occur- ring in the soil are quite indispensable to the life of higher plants, since they aid in the preparation of the food for plants. Next to the soil, the intestinal canal of animals sup- port a large and varied bacterial flora. The blood, th& different internal organs such as the liver and spleen, or the muscles contain few or no bacteria, but in the alimentary tract from the mouth to the rectum, bacteria are found in varying numbers. Water is also to be looked upon as one of the natural habitats of bacteria, for it always contains food sub- stances in greater or less abundance. As a rule the number of bacteria in water depends on the relation of the water to the soil. Surface streams usually contain many bacteria, especially when the water from culti- vated fields drains into the stream. In shallow wells that receive the drainage from the upper layers of the soil, bacteria also abound. As the water percolates through the soil the bacteria are filtered out, hence, the water from deep wells contains very few. The number 14 Agricultural Bacteriology. found in the waters of rivers, especially those of con- siderable size, and in lakes is usually small since there are many factors that tend to destroy the bacteria. Most of the other places in which the bacteria are found are not to be looked upon as natural habitats, Tjut rather as secondary sources. The bacteria may ba found almost anywhere, because dust from the soil finds its way into or onto every object. The bacteria of the air come from the soil, being carried up by air currents. The number in the air depends on the amount of dust present; hence, in cities many are found in the air, in the open country far less, and in the air over large bodies of water, none may be present. The bacteria found in all articles of food come from one of the natural habitats of this form of life. By keeping foods as clean as possible a great deal can be done to preserve them. CHAPTER II. ARTIFICIAL CULTIVATION OF BACTERIA. The bacteria are so small that many thousands of them must 'be present in a mass before they can be seen with the naked eye. The necessity of having masses of bacteria of the same kind for study in the laboratory thus becomes evident, and since such masses do not oc- cur in nature it becomes necessary to grow them arti- ficially. Food substances. The substances used in the labora- tory upon which the bacteria can be grown are of ani- mal or vegetable origin. These bacterial foods or * ' cul- ture media, ' ' as they are technically called, may be pre- pared from various vegetables, as potatoes or beets. Broths made from meat or beef-extract are constantly employed, as are milk, coagulated egg, and blood-serum. The composition of these natural media are often modi- fied through the addition of various qualifying sub- stances, such as sugar, peptone, and glycerine, in order to make them more suitable for the growth of certain kinds of bacteria. All culture media when prepared from ordinary ma- terials contain more or less bacterial life, because of the presence of the organisms in the ingredients themselves, and due to the inevitable contamination during the proc- ess of manufacture. If the culture media are to be kept for any length of time they must be freed from all living bacteria and 16 Agricultural Bacteriology. kept so. For this purpose the various media are placed in glass vessels, such as flasks and tubes, which are stoppered with cotton-wool. This cotton plug allows: the air to pass freely in and out of the vessel, but re- moves all dust and bacteria that % the air may contain. It serves to prevent the bacteria from entering tlje ves- sel from the outside as effectively as though the vessel were sealed air tight. Sterilization. After the media is thus protected from future contamination, the contained bacteria are killed 1 by heating the media to the boiling point for a short time on each of three successive days. The vegetating cells are easily killed but the spores are not destroyed by the first heating. If the media is stored at ordi- nary temperatures, many of the spores will germinate and form cells before the second heating. The remain- ing spores will usually sprout by the third day and are then destroyed. A heating treatment applied as pre- scribed will usually render any food medium "sterile,'' i. e., absolutely free from all living bacteria or their spores. When so treated it -will keep for an indefinite period if protected from drying. The vegetating cells and also the spores may be killed at one heating but the exposure must be very prolonged or it must be made in a closed chamber in which steam is generated. In this latter condition the temperature can be raised quickly to a point considerably higher than the boiling point so that the spores will be killed in a few minutes. This same process is used in the canning of vegetables, such as corn and peas. All such foods must be sterile or they will soon spoil. The containers used to hold the media are usually of glass and are rendered free from all living bacteria by Artificial Cultivation of Bacteria. 17 heating them in a hot-air oven. This method can not be used for culture media since it would burn the same. Determination of the number of bacteria in sub- stances. The extreme minuteness of the bacteria makes it impossible to count them individually. To determine the number present in any material it is necessary to FIG 6. PLATE CULTURE. Each of the dots is a colony that has been formed by the growth of a bacterial cell embedded in the solid medium. By counting the colonies, the number of bacteria in the material examined is determined. separate each organism from all others by an appre- ciable distance. The organisms are then placed in an appropriate food substance in which they are held in place, growth occurs and a mass large enough to be 18 Agricultural Bacteriology. seen by the naked eye is soon obtained. If, for exam- ple, the number of bacteria in a sample of water is to be determined, the conditions mentioned above are ob- tained in the following way. A definite amount of water is intimately mixed with a small amount of beef- broth to which gelatin has been added. This furnishes a medium which is solid at ordinary temperatures, but which can be easily melted, and by cooling changed back to a solid again. If the gelatin is at once cooled after the water has been mixed with it, the bacterial cells will be held in place in the now solid medium. The gelatin is then placed under favorable conditions for the growth of the bacteria. The cells begin to increase in number, and as their progeny can not move away, the resulting mass of cells soon becomes large enough to be recognized by the unaided eye. In liquid media, such as beef -broth, the bacteria are not held in place and the liquid becomes uniformly turbid because of the distri- bution of the bacteria in it. Each of the masses of growth, technically called a "colony," is the progeny of a single cell. Thus, if the colonies are counted, the result will be the number of bacterial cells present in the substance at the time the cultures were made. In order to make the counting of the colonies easy the mixture of gelatin and water is placed in a shallow glass dish so as to form a thin layer of solid gelatin on the bottom of the dish. It is protected from the bacteria of the air by a glass cover. It is essential if one is to determine how many bac- teria are present in the amount of water used, that each of the colonies on the culture plate is the result of the growth of an organism present in the water. This ne- cessitates that the food medium, the glass dish and Artificial Cultivation of Bacteria. 19 everything coming in contact with the culture in any way is wholly free from living bacteria, i. e., sterile. Many substances frequently contain so many bacteria that it is impossible to add a small enough amount to the gelatine directly, and not have the cultures so thickly dotted with colonies that it would be impossible to count them.' To overcome this difficulty a small but definite amount of the substance is added to a definite amount of sterile water, and intimately mixed. A quantity of the mixture is then added to the melted gelatin. In this manner it is possible to obtain 1-1000 of a drop of water or milk, a procedure that will be seen to be necessary when it is known how many qf the bacteria there may be in a drop of these liquids. Pure cultures of bacteria. Since each colony has re- sulted from the growth of a single cell, it follows that all of the cells of the colony are of the same kind. If a small bit of the mass of growth is transferred from the original colony to a tube of fresh food, the resulting growth is known as a "pure culture." If some other form of bacteria should accidentally fall into the tube from the air when the tube is opened, the culture no longer contains a single kind but a mixture and is now called an impure or mixed culture. The shape and appearance of the colonies of the dif- ferent kinds of bacteria differ as do their growth on various media. These differences often aid the experi- enced bacteriologist in determining the kind of bacteria in the materials examined. In order to separate a pure culture from a mixture of many kinds or in order -to determine the kinds of bac- teria present in any substance, essentially the same method is used as described above. 20 Agricultural Bacteriology. Use of the microscope. The microscope of necessity is a tool of vital importance to the bacteriologist. The extreme minuteness of the bacteria require that an in- strument magnifying several hundred diameters be used. Even then the bacteria in an untreated condition are very difficult to see on account of their transpar- ency. In order to make them more easily visible a very small amount of the substance in which they are grow- ing is spread on a thin piece of glass and allowed to become perfectly dry. The organisms are then killed by heating gently and are treated with various stains which impart a bright color, red, blue, or purple as the case may be, to the bacteria. Just as a red glass is seen more easily than a piece of perfect plate glass so the stained bacteria are more easily seen than the unstained forms, and, moreover their size, exact form and other characteristics are more easily determined. Appearance of the bacteria under the microscope. The appearance of the individual bacterial cell under the microscope can not vary widely because of the limi- tation that the bacteria are one-celled structures. The spherical forms always appear as tiny dots, the rods as dashes, and the spiral forms as dashes or lines more or less curved in various ways. The size varies somewhat, as do the arrangement of the cells with reference to each other, but the microscope rarely enables one to tell the kind of bacteria present in a culture. The ap- pearance of the growth on a large number of media must be noted, as also the changes produced in these different food substances. These serve as aids to the appearance under the microscope in determining the kind of bacteria one has at hand. Artificial Cultivation of Bacteria. 21 Handling of bacteria. The bacteria are handled in the laboratory and are transferred from one culture tube to another containing fresh food by means of small platinum wires inserted in glass handles. These wires are rendered germ free by heating them in a flame be- fore they are used. By keeping the culture tubes plugged with cotton, by careful use of the inoculating needle, and by using care at every step, the bacteriolo- gist works with the most dangerous disease-producing organisms without danger to himself. Use of experimental animals. In the study of the disease-producing or pathogenic bacteria, it frequently becomes necessary to use for inoculation purposes small animals, such as guinea pigs, rabbits, white mice, and rats. Some forms of bacteria can not grow on any of the artificial media but may develop in the bodies of animals, so that animal inoculation becomes a necessity in determining whether any particular kind of organ- ism is able to produce disease or not. Incubation of bacteria. Many of the bacteria have acquired parasitic properties and grow naturally only in the bodies of animals. Such is the case with the tu- bercle bacillus. If such types are to be artificially propagated, the cultures must be kept under conditions simulating the animal body. Hence incubators to main- tain the cultures at the same temperature as the animal body are more or less essential in bacteriological work. SECTION II. RELATION OF BACTERIA TO MILK AND OTHER DAIRY PRODUCTS. CHAPTER III. CONTAMINATION OF MILK. A large part of the farming population of the country is actively interested in the production of milk. Every one is interested in milk from the food standpoint. How this important food product can be produced un- der clean and healthful conditions therefore appeals to every one, producer and consumer alike. Milk a perishable food. Milk is produced on the farm, (1) for sale in the tOAvns and cities, (2) for use in the manufacture of butter and cheese. In order that it shall find a ready market in the city and that the but- ter and cheese made from it shall be of the highest quality, it is necessary that the milk be produced and handled under improved conditions. No other food is produced under circumstances that permit of the intro- duction of such an amount of dirt and bacteria as are found very frequently in milk. At every step it is nec- essary to consider the relation of bacteria to this food product. Many of the most important human foods are perishable. Eggs, meat, many fruits, and vegeta- Contamination of Milk. 23 bles rapidly undergo changes that render them unde- sirable, or even unfit for human food. Milk is the most perishable food of all. Produced under ordinary con- ditions and with no precautions taken to preserve it during the warmer periods of the year, it is unfit for use in twenty-four hours. There are two reasons for this rapid deterioration : (1) gross contamination, (2) its nature and composi- tion. The surroundings in which milk is produced al- ways make infection easy. The high nutritive compo- sition and the dilution of its food ingredients make it admirably adapted as a medium for bacterial growth. Many of the bacteria produce changes in the milk which injure the quality of the butter and cheese. It thus be- comes important to prevent as far as possible the intro- duction of the bacteria and to check their development in the milk. Contamination of milk. Tn order to prevent the bac- teria from getting into the milk, it is necessary to know the sources from which they come, and to become ac- quainted with practical means of exclusion. Unless the sources are recognized and something is known of their relative importance, numerous things will be done that are unnecessary, and often the essential things left un- done. The subject of the contamination of milk is the most important and fundamental one in dairy bacteriology. At every step in the production of milk and in its treat- ment on the farm the farmer is confronted with this subject. The returns he receives from his milk are often decided by the wisdom with which he meets the problems concerned in the production of clean and healthful milk. 24 Agricultural Bacteriology. The contamination of milk must be considered from two points of view: (1) the economic, that is the con- tamination with thos'e forms of bacteria that cause the milk to sour, (2) the hygienic, the contamination with those forms of bacteria that produce disease in human beings. Both of these phases of milk contamination are becoming more important each year, as more is learned of the ways in which diseases are spread and as the rapid growth of the cities makes it necessary to draw milk from more distant sources. Condition of milk when formed in the udder. When the milk is secreted in the udder of a healthy cow it is sterile. The various internal organs and the blood are practically sterile in healthy animals, hence any sub- stance which is formed from the blood must be sterile. Condition of the milk when drawn from the udder. If & sample of milk is drawn into a sterile vessel in such a way as to prevent all external contamination, it will be found to contain a greater or less number of bac- teria, which must have come from the udder of the ani- mal. The udder is composed of the secreting tissue held in place by the fibrous connective tissue. From the upper part of the glandular secreting tissue, small tubes lead downward, joining each other until they communicate with a small cavity known as the milk cistern, which holds about one half-pint. From this cistern the milk flows into the teat which is guarded by muscles, at the top and bottom. A normal contraction of these muscles keeps the milk from leaking out of the udder. The end of the teat inevitably becomes soiled with material containing bacteria. Through the opening of Contamination of Milk. ^ 25 the teat the bacteria make their way up into the milk cistern and to a less extent into the milk ducts, and e\en to the secreting tissue proper. Many forms un- doubtedly enter but only a few are able to grow to any extent. They are harmless guests and cause the cow no trouble. They are found in the milk when it is drawn, usually several hundred in every cubic centimeter. Since the bacteria enter the udder through the teat, one should expect to find the greater number in the lower part of the udder, where they would be washed out dur- ing the first part of the milking. As a rule the first streams from each teat contain a larger number of or- ganisms than those subsequently drawn. This source of contamination can not be wholly avoided. Material reduction in numbers may be pro- duced by excluding the fore-milk i. e., the first few streams drawn from each teat. Such milk should be drawn into a separate container, not milked on to the floor. It may be used for feed. It is always low in bat- ter fat. While such a method will reduce the number of bacteria in the milk slightly, it has no particular effect upon the keeping quality of the milk since the or- ganisms found in the udder grow very slowly at ordi- nary temperatures and produce no marked changes in the milk. Some times the udder is invaded by harmful kinds of bacteria which grow rapidly and cause an inflammation of the gland, which diseased condition is known as gar- get. See p. 144. Contamination from the animal. Milking is almost always carried on under conditions, that must be called unclean when it is considered that human food is being prepared. Conditions are tolerated in the barn that 26 % Agricultural Bacteriology. would not be allowed in the kitchen, and yet, in both cases the preparation of human food is in progress. Of neces- sity it is difficult to produce milk in a wholly clean en- vironment; yet every effort should be made to improve the barn conditions as much as possible. During the milking, dust, dirt, and manure particles are dislodged from the udder and flanks of the animal by the motions of the milker. These particles inevit- ably fall into the open pail. The amount of dirt and manure thus introduced into the milk depends almost en- tirely on the cleanliness of the animal. If the flanks and udder are coated with manure and dried mud, a very large amount of dirt will enter the milk and nothing can prevent it. As has been previously mentioned a prominent source of bacterial life is the intestinal canal of animals. In the manure are found an immense number of bacteria. It requires but a small amount of manure to add many thousands of bacteria to every drop of milk. The fact that the kinds of bacteria derived from the manure pro- duce, in the main, injurious changes in the milk (bad odors and tastes) affecting not only the milk but the butter and cheese as well, makes it highly desirable to reduce the contamination from this source as far as pos- sible. The dust from the skin of the animal contains large numbers of bacteria. Esten found in the dust taken from a curry comb 207,000,000 organisms per gram (1-30 ounce) . The hairs, even those from the cleanest cows, have large numbers of bacteria on them. Prevention of contamination from the animal. In order to prevent the milk from being contaminated with large quantities of mud and manure, the animal must be Contamination of Milk. 27 kept clean. The cows must not have access to mud holes, the yards should be so arranged that they can not become muddy during the wet times of the year. The arrangement of the stalls should be such as to- prevent contact of the body of the animal with the ma- nure. This can only be accomplished by using a manure drop, i. e. a deep gutter. The animal can also- be kept clean by the use of a stall that requires her to stand well to the rear and forces her forward when ly- ing down. Many of the patented stalls seek to accom- FIG. 7. THE MODEL STALL. A stall of this type keeps the animals clean and aids greatly in the production of clean milk. plish this in a variety of ways. Fig. 7 represents a stall that accomplishes this purpose in a most successful way. The essential feature of this stall is the placing of a two by three inch piece of timber across the floor of the stall. This piece is so placed that when the animal stands with her head close to the slatted manger, it will be just in front of her hind feet. Thus when the animal 28 Agricultural Bacteriology. is standing, her hind feet will always be back of the strip and the manure fall well to the rear. The animal soon learns that it is not at all comfortable to lie on the -strip and thus crowds to the front on lying down and is out of contact with the manure. The clean condition of the cows in the accompanying illustration is to be noted. The photographs were taken in the early spring before the cows had shed their winter coats. Less than one hour per day of one man's time was spent in cleaning the thirty animals of the herd. A stall that accomplishes this purpose, together with plenty of clean bedding is all that is needed to keep the cattle clean. These things are within the reach of every farmer. Concrete is often used as a floor and is very desirable on account of the easier cleaning. It is de- sirable, especially in the colder parts of the country, to cover the concrete of the stalls with wood. Other things may be done that will greatly reduce the contamination from the animal. The long hairs should be clipped from the udder and flanks and the tail should also be clipped. The short hair holds much less dirt and the animal can be cleaned much easier in case she becomes soiled. Cleaning with card and brush will also insure the removal of much of the loose dirt and hair from the skin. This treatment should be given some time before the milking time, on account of the dust produced. The udder and flanks should be wiped with a damp cloth just before milking. This serves to remove much of the dust and prevents the dislodgment of the finer dust particles during the milk- ing process. Improved milk pails. In order to still further dimin- ish the contamination from the animal the use of a pail Contamination of Milk, 29 with a small opening is desirable. The larger part of the dirt entering the pail comes from the flank rather than from the udder. The dirt is dislodged by the eon- tact between the milker and the flank of the animal. All this material finds its way into the common large topped pail. If the opening is restricted to six inches, the exposed surface is greatly lessened. A six inch opening is one-fourth as large in area as a twelve inch. The reduction of contamination will be in still greater proportion as with the small topped pail the opening is directly beneath the udder during the milking. The dirt from the flanks does not find its way so readily into this pail as it does into the ordinary pail. Stocking has shown that under ordinary barn condi- tions the number of bacteria found in milk drawn into such a covered pail was but five per cent of the number found when an ordinary pail was used, and with very dirty cows but 3 per cent. Many forms of pails of this character have been sug- gested. All seek to reduce the size of the opening in one way or another. Some of the most practical forms are represented in Figs. 8 and 9. In some of the pails, strainers of cloth or cotton are used, although brass wire gauze is effective and easier cleaned. The use of the milking machine avoids a large part of the contamination from the animal since the milk is drawn directly into a closed tube through which it passes to the receiving can. Contamination from utensils. The various utensils used in handling milk always contain bacteria, the number depending on the cleanliness of the utensnX which is determined (1) by the manner of washing, (2) the construction of the utensil, (3) the condition of the 30 Agricultural Bacteriology. utensil. Cheap tin-ware is usually made with folded seams which are not flushed with solder. The milk penetrates into the crevices thus formed and can not FIG, 8. IMPROVED MILK PAILS. The small opening is very efficient in keeping dirt out of the milk. FIG. 9. IMPROVED MILK PAILS. The Stadtmueller pail and the Truman pail, two of the most practicable of the small topped pails. l>e removed by washing. As the utensil becomes older the seams become more and more open and a greater amount of material accumulates in them to find its way into the milk. Old battered and rusty tin- ware can not Contamination of Milk. 31 be well cleaned by washing unless the facilities for such purposes are much better than on the ordinary farm. All tin-ware should have a smooth and unbroken sur- face. Even the roughness due to the accumulation of the white layer (milk stone) on the pails and cans ren- ders them much more difficult to wash and hence in- creases the contamination from them. Pressed tin- ware is preferable but if the utensils are made with seams the depressions should be thoroughly flushed with solder. The farm cream-separator is a utensil that needs especial care. Often it is not the custom to take the machine apart after each period of use and wash it thor- oughly. When used for the evening milk it is often only rinsed out by passing water through the bowl. The slime that accumulates on the wall of the bowl can not be removed in this way, and between the periods of use, especially during warm weather, the bacteria grow rapidly in the slime. When milk is passed through the separator in the morning, a large part of these bacteria find their way into the milk and cream and may cause undesirable fermentation changes in them. The sepa- rator should be taken apart, well washed and scalded after each period of use. Much loss is caused to the farmers of the country due to the diminished returns received from butter made from cream separated in dirty farm separators. In fact, it is well recognized that the general introduction of the farm separator has led to a deterioration in the quality of butter. Contamination from factory by-products. The farmer is accustomed to return to the farm the skim milk or whey from creamery or factory in the milk can. If the can is at once emptied and thoroughly washed, no 32 Agricultural Bacteriology. especial harm results. In the whey, especially in that from unclean tanks, are found injurious forms of bac- teria that find their way from the whey to the cheese- vat through the medium of the contaminated and poorly washed milk can. In order to avoid this source of loss a separate set of cans should be used in which to return the by-products to the farm. At some cheese factories and creameries the by-products are heated to the scald- ing point before being returned to the farm. When so handled the results are essentially as good as if a sepa- rate set of cans were used. Washing milk utensils. All milk utensils should be washed as soon as possible after using, for if the milk is allowed to dry on the surface of such containers it is very difficult to remove. They should be rinsed with cool or hike-warm water, then thoroughly washed with a hot solution of a washing powder, as Wyandotte or a similar preparation, using, preferably, a stiff brush for scrubbing. The use of soap and soap powders is to be avoided for they are difficult to remove by rinsing and are not as effective in the removal of the milk and grease. The utensils should be well rinsed in boiling water, using a large quantity, so that they will be thor- oughly scalded. If the scalding is done with a small amount of hot but not boiling water, the bacteria on the walls of the utensils will not be destroyed. After scalding they should be drained but never wiped. If sufficient hot water is used, the utensil will be heated so that it will dry quickly with no further attention. The clean utensils should be stored in a place free from dust. Wherever steam is available, the cleansing can be- made much more effective by steaming, after rinsing Contamination of Milk. 33 with clean water. By this treatment it is possible to destroy practically all bacteria. For this reason most city dairy companies and even some cheese-factories and creameries wash the cans of their patrons. Where steam is not available the utensils may be immersed in boiling water. Some such treatment is especially recommended to the milk producer supplying milk to the city market. The milk producer who uses a milking machine avoids one source of contamination only to meet an- other unless care is taken in the handling of the ma- chine. The rubber tubes used in connection with the machine are very difficult to clean. They should be well rinsed after use and at once placed in a 3 per cent formaldehyde solution in such a way that the entire tube will be filled with the solution. This will prevent all growth of bacteria in the tubes. If some such treat- ment is not given the tubes, the milk drawn by the ma- chine will be found to contain more bacteria than that drawn by hand. This is due to the k fact that it is im- possible to remove all of the milk from the tubes by rinsing them, and since it is also impossible to dry the inside of the tubes, conditions are favorable for bac- terial growth with the result that, when the tubes are next used, the bacteria pass into the milk. The milking machine is an aid in the production of clean milk only when used in an intelligent and careful manner. Contamination from the air. In the barn air more or less dust is to be found, coming from the feed, bedding, and dried manure. The dust particles act as floats for the bacteria, and when the dust settles into the milk pail, the milk is contaminated with bacteria. The barn air should contain the minimum of dust at milking 34 Agricultural Bacteriology. time. This condition is to be obtained by not feeding hay or other rough, dry fodder shortly before milking, by not carrying on any dust-producing operations as bedding, sweeping, etc., just before milking. The ceil- ings of the stable should be tight so that dust and dirt can not fall from the floor above and the walls and ceil- ings should be free from cobwebs. The stable should be of such construction as to be easily kept clean. Abundant light should be provided, because the same is beneficial to the cattle and renders evident dirty conditions. Abundant ventilation means less dust in the barn air and hence fewer bacteria to fall into the milk. Contamination from the milker. The milker is to be looked upon as an important factor in milk contamina- tion. His habits with reference to personal cleanliness mirron themselves in the amount of dirt he will get into the milk drawn by him. The hands of the milker should be 'clean, for some milk is certain to come in con- tact with them on its way to the pail. The suit which is worn during milking should be kept for that purpose alone and should be washed at frequent intervals. The milking should always be done with dry hands using the whole hand and stripping with the fingers avoided as far as possible. Vaseline can be used on the hands or on the teats of the cow if desired. Influence of food on contamination of milk. It is be- lieved by many that the bacteria in the feed or water consumed by the cow pass directly into the milk by way of the udder. From what has been said it is evi- dent that such can not be the case. The feed may in- fluence the kind of germs in the milk by influencing Contamination of Milk. 35 the kind in the manure. Unsavory as it may sound, a large part of the bacteria in the milk have their origin in the manure, which, in one way or another, is added to the milk. If spoiled or wet feeds such as brewery or distillery slops are fed, intestinal troubles may result with a change in the kind of bacteria found in the manure. Only in this way can the feed influence, in any consid- erable way, the bacterial content of the milk. Moldy and dusty feeds should not be used. The straw used for bedding should be clean. Horse manure should not be used for bedding in the cow stalls. If the feed is such as to render the manure very thin, it is much more difficult to keep the animals clean, thus influencing the number of micro-organisms found in the milk. The in- fluence of impure water is due usually to the fact that the cattle have access to a stream or pond. By wading about in the water their udders are soiled, and at milk- ing some of the water bacteria get into the milk. Absorption of odors. Milk absorbs many but not all odors very easily and for this reason it should be kept in a place free from all pronounced odors of any kind. The odors of certain fruits, as bananas, and the odor of strong silage are quickly absorbed by milk. It is a popular belief that milk will not absorb odors when it is warmer than the surrounding air, but experimentally it can be easily demonstrated that the opposite is true, the warm milk absorbing the odors more rapidly than the cold. For this reason milk should always be re- moved from the stable as soon as it is drawn from the animal, for in the stable there is quite certain to be some odor arising frc'n the manure, the animals them- selves, or the feed. The danger of thus tainting the 36 Agricultural Bacteriology. milk is much less in a well ventilated stable. Milk should never be strained, aerated or separated in the stable. Odors absorbed from the feed. In certain feeds such as turnips, cabbage, rape, and in many weeds are found substances that give to the various plants their charac- teristic taste and odor. If a milch cow is fed on such plants, the peculiar flavoring substance will pass through the system and reappear in the milk, often giv- ing to the milk such a peculiar taste as to render it useless for direct consumption or for butter and cheese making. Such feeds should never be fed except in limited quantities immediately after milking so that the volatile odors may be eliminated from the body be- fore the next milking. Green rye and strong silage should be fed with care or the milk will be injured. The milk from cows receiving medicine in any form should be excluded from the supply since many drugs pass from the body tissues to the milk. Such milk may cause illness, especially in children, and injure the quality of butter and cheese. The constituent of milk that causes it to absorb odors so readily is the fat. Butter is more easily injured by absorption of "odors than is milk, as is not infre- quently noted when it is kept in an ice-box with fruits, etc. If the milk is tainted, the butter and cheese are very certain to show the same flavor. This can be dem- onstrated by feeding cows on rape and making cheese from the milk. The ripe cheese will possess the flavor of rape to such an extent as to be worthless. Contamination under winter and summer conditions. It is often thought that the milk produced in summer is much cleaner than the winter milk. This is less true Contamination of Milk. 37 than is usually believed, for on too many farms the cattle have access to places where they become soiled with mud. The number of bacteria gaming entrance to the milk in the summer may be as great as in winter. The udder comes in contact with the ground when the animal lies down in the pasture or in the yard. The dust thus accumulated is not especially visible, but its load of bacteria reaches the milk. The milk house. The room in which the milk is to bo strained and cooled, preferably, should not be in the barn, but at a short distance from it. It should be far enough away so that the odors of the barnyard will not be present. The room should be provided with a con- crete floor, with abundant light and good ventilation. The windows and doors should be well screened so that flies may not have access to milk and the utensils. As will be seen later flies are often carriers of disease- producing bacteria. Clean milk. The demand for clean milk is increas- ing rapidly. It is desired not only because it keeps longer, tastes better, and finer butter and cheese can be made from it, but also because dirty milk means sick- ness and death to the children, not so much to the chil- dren of the country, for these drink fresh milk only a few hours old before the bacteria carried into the milk in dust, mud and manure have had a chance to grow and thus injure the milk. But the city child consumes milk which is at least a day old and very often two or three days old, in which the bacteria have developed to an enormous extent. Clean milk is desired for cleanliness sake. Every one wishes his food prepared and handled in a clean manner. Manure in milk is no more to be tolerated than it is in bread, and it is no more 38 Agricultural Bacteriology. necessary that it be present in the former than in the latter. Essentials in the production of clean milk. The statement is frequently made that the production of clean milk means expensive stables, elaborate equip- ment, and much expenditure of time and labor, but such ideas are far from correct. The essential condi- tions are (1) clean cows, clean because they are not al- lowed to lie in their own excreta, or are not forced to wade in muddy yards; (2) clean utensils, well washed and sterilized; (3) clean barns; (4) clean men who take pleasure in keeping their stables and animals clean, and who recognize the important sources of contamina- tion of milk and avoid them, while omitting the non- essential things that figure so largely in many of the directions for the production of clean milk. The expense of producing clean milk need be but slightly more than that involved in the production of the ordinary grade of milk. The same animals, the same feed, the same time spent in feeding and in caring for the cattle, supplemented by a slight amount of at- tention directed to the important points is all that is needed. Infection of milk with disease-producing bacteria. Milk is often a means by which disease is spread. It may serve to convey the disease-producing germs from one animal to another, from the cow to man, or from one person to another in the case of some diseases not found in the cow. Of the diseases common to man and cattle, tuberculosis is the most important. Of the diseases found only in man but which are spread by means of milk, typhoid fever and diphtheria are of most concern. Contamination of Milk. 39 Tuberculosis of the cow. As will be seen in a subse- quent chapter, the tubercle germs may be given off from the body of the diseased animal in the "open" stage of the disease. They may come from the lungs, intes- tines, and udder. Leaving the body from any of these sources they may reach the milk. In tuberculosis of the lungs the cow coughs up material from these or- gans and swallows it. It is digested, but the tubercle bacteria it contains pass off from the body in the ma- nure. When the disease affects the intestines, the ma- nure also contains the tubercle organisms. The bacteria are carried into 'the milk with the ma- nure aird barn-dust. The udder is often affected by the disease. In this case the milk is certain to contain large numbers of the tubercle organisms, although it may be perfectly normal in appearance and taste. Milk containing tubercle bacilli is often a means of producing the disease in man, especially is this true in the case of children, who use larger quantities of milk than do adults and who seem to acquire tubercu- losis by way of the intestinal tract more easily than does the adult. If milk containing tubercle bacilli is fed to calves and hogs, they are certain to be infected. In order to be certain that the milk does not contain any tubercle bacilli it must have come from healthy animals. Many tuberculous cows may give milk which is perfectly healthful, but sooner or later the milk of such animals is certain to contain the organisms of the disease. No one can tell when this condition obtains, hence the only safe way is to reject all diseased animals from the dairy herd. Miscellaneous diseases of the cow. Certain other diseases may be acquired by man from cattle through 40 Agricultural Bacteriology. the milk. Foot and mouth disease, a common disease of cattle in Germany and France, is often so acquired. Lumpy jaw or actinomycosis may affect the udder and the organisms be given off in the milk. Inflammation of the udder or garget, especially contagious garget, is caused by bacteria that may produce throat and intesti- nal troubles in man. The milk of any animal which shows any fever in the udder or whose milk is any way abnormal should be kept from the general supply. It may not be harmful, but it is the secretion of a diseased gland and should not be used as human food. The milk of cows having chronic diarrhea, inflammation of the bowels, or that have not cleaned well after calving should be rejected. In short the milk of any animal that is sick or that is receiving medicine should not be used for human food. Typhoid fever and diphtheria. Typhoid fever is an intestinal disease of human beings. The bacteria are taken into the alimentary tract with food or drink that has been contaminated in some way. The organisms are given off from the body of the patient in the feces and urine. These materials find their way into the sewage which is so frequently discharged into rivers and lakes that .also serve as sources of water supply. When privies are used as in the country, the typhoid bacteria may reach the farm well by means of the water percolating from the privy vault through the ground into the well. If such contaminated waters are used to wash milk utensils, the milk may be con- taminated with the typhoid fever germs. Milk uten- sils are frequently rinsed with cold water just previous to using. Some of the bacteria are certain to enter the milk if the water is polluted. Contamination of Milk. 41 The contamination of the milk may also occur through the agency of a person acting as a nurse and also handling the milk. The hands of the nurse are easily soiled with the discharges of the patient, partic- ularly the urine which often contains many typhoid bacilli, some of which may thus find their way into the milk. The patient after recovery still gives off typhoid bacteria from his body for a longer or shorter period and thus may serve to contaminate the milk. Such people, known as "typhoid carriers," are one of the most important means of spreading the disease. The ordinary house fly is one of the most common means of infecting food with the typhoid bacillus. If it has access to any infectious material, it may readily carry the bacilli to the food in the kitchen or to the milk in the barn or milk house. The privy vault should be so arranged that flies can not enter it. The dwelling house and also the milk house should be pro- vided with screens at the doors and windows. In order to prevent the spread of typhoid fever all discharges from the patients should be thoroughly dis- infected. No one who has anything to do with a typhoid patient should have anything to do with the milk in any way directly or indirectly. The patient, after recovery, should not handle dairy products or have anything to do with milk utensils until the con- sent of a physician is obtained. This should be the in- variable practice on the farm, in the cheese-factory, the creamery and in the city milk-depot, for experience has shown that a single case of typhoid has often been the means of infecting the milk supply, thus producing widespread epidemics. There is no danger of trans- 42 Agricultural Bacteriology. mission of the disease to stock as none of the domestic animals acquire typhoid fever. The tubercle germ can not grow in milk, when drawn from the animal ; the typhoid bacillus on the other hand is able to grow in it at ordinary temperatures. Only a drop of polluted water or the most minute particle of matter containing typhoid bacteria is necessary to seed the milk. Because of the growth of the bacilli, the milk may contain large numbers of them by the time it, reaches the consumer. The diphtheria bacillus grows in the throat and in the nasal passages of the affected person. The only way in which it can reach the milk is through the me- dium of the nurse, whose hands may have become con- taminated or from the patient after recovery, for un- fortunately recovery does not mean that the diphtheria bacillus has disappeared entirely from the throat and nasal passages. They may persist there for months. The diphtheria bacillus like the typhoid organism can grow in milk at ordinary temperatures. The milk from farms on which diphtheria is present should not be sent to the city market. The same rules relative to the patient should be enforced as with typhoid fever. Scarlet fever is also spread by milk and the same precautions should be observed as in the case of the diseases previously mentioned. Intestinal troubles caused by milk. During the sum- mer months the death-rate amongst milk-fed children in the cities is very high. This is due, in a large measure, to the intestinal troubles that are occasioned by improper food. Milk on account of its quick per- ishability is especially liable to produce troubles of this sort. The death-rate of children is greatest among OF THE Contamination of Milk. 43 the poorer people who are either unable to keep their milk supply in good condition on account of the lack of ice, or who do not appreciate the proper handling of this food product. These troubles are not caused by any specific kinds of bacteria but by many kinds that get into the milk with the dirt and manure. As was previously pointed out, the country child drinks fresh milk, the child of the tenement-house district, old milk. Not the filth, but the bacteria associated with it, are the cause of the trouble. The remedy is clean milk and as fresh as possible to the consumer's door. Poisoned milk. Occasionally milk is the cause of trouble due to the fact that it contains poisonous com- pounds formed by bacteria in their development. Nor- mally the acid-forming bacteria prevent the growth of the harmful kinds. In ice cream, poisonous products are more often found than in milk, due to the practice of storing cream during the cooler times of the sum- mer in order to have a supply for the warmer periods. Some forms of bacteria can grow in the milk and cream at the storage temperatures and produce poisonous products. CHAPTER IV. PRESERVATION OF MILK. Necessity for preservative measures. It is impos- sible to produce milk that does not contain bacteria. Some will be present no matter how much care is ex- ercised since those forms from the interior of the udder een carried on, the disease is very widespread. In soma of the German states 30 per cent of the cattle are dis- eased ; in Belgium 48 per cent ; in Denmark after fifteen years of warfare against it, the percentage of dairy cows affected has been reduced from 40 to 10 per cent; in England 35 per cent of the cattle are affected. In some of our eastern states, as Massachusetts, 26 per cent of the dairy cows have the disease. The amount of the disease is less in the western states, probably from 5 to 10 per cent of the milch cows of Wisconsin, Minnesota, Iowa anji Illinois are affected. It is not evenly distributed, but is most prevalent in those districts where improved dairying has been longest carried on, and where buying and selling of milch cows is general, as in the districts furnishing milk to the cities. It is more often found in pure-bred herds than in those of common stock, not because pure-bred cattle are more susceptible, but because more animals are bought into and sold from such herds. There is little or no differ- ence in the susceptibility of the various breeds; Jerseys are free from it on the island of Jersey, but acquire it, when brought in contact with diseased cattle. The beef- breeds are as easily infected as any of the dairy breeds. It is more often present in large herds than in small ones, as each animal purchased may be the means of in- troducing the disease into the herd. Distribution and appearance of diseased tissues. The disease is commonly associated with an affection of the lungs and indeed this organ is most often attacked. Every part of the body, however, may be diseased heart, liver, spleen, muscles, brain, and skin may be affected. The lymph glands that are found in the neck, along 112 Agricultural Bacteriology. the windpipe, and close to the intestine are usually the- first to be affected. In making a post-mortem examina- tion of the suspected animal, the parts that should be examined are the lungs, the lymph glands mentioned above, liver and the spleen. The tubercles vary greatly in size, from a pinhead to the size of a hazelnut or walnut. When opened, the smaller tubercles are usually of a light gray color throughout, or may show at the center a yellowish spot. The larger tubercles will usually contain yellowish: FIG. 12. TUBERCULOUS OMENTUM. The omentum, a" membrane of the abdominal cavity, is normally smooth and thin. It is here studded with masses of small tubercles. From a gener- alized case of bovine tuberculosis. material and in many of the organs, as in the liver r spleen, and lungs, tubercular abscesses of varying size- may be formed. Some of the lymph glands become very greatly enlarged. They may be filled with creamy pus, or with a hard, gritty, yellowish substance, which is produced by the accumulation of lime salts. On ac- count of the yellow granular appearance, the contents Tuberculosis. 113 are often said to look like corn meal. The healthy lymph glands are of uniform color throughout, or in the older animals they may be filled with a black pigment. The tuberculous gland will, on section, show a larger or smaller diseased area, apparent by its yellow color. The lungs of a healthy animal are light pink in color and spongy in texture; when tuberculous, the tissue is consolidated, abscesses or affected areas appearing in the lung tissue or even raised from the surface. The bron- chial glands located at the fork of the windpipe and imbedded in the lung tissue are often early affected. The diseased organs are usually much enlarged and owing to the consolidation of tissue may be very heavy. The udder is sometimes affected. The normal udder should be uniformly soft; the tuberculous udder often contains hard bunches or nodules. As the disease progresses an entire quarter may become enlarged, and very hard. There is no fever or painful swelling as in garget. Tuberculosis of the udder is important because the milk is then certain to contain the tubercle or- ganisms. The bacteria are discharged from the body of an animal in a number of ways. The tubercles in the lungs may discharge their contents into the air passages; the material is coughed up, a portion ejected from the mouth during the act of coughing, the major -part being swallowed. The sputum is digested, the tubercle bacilli set free, and they pass unharmed through the stomach and intestines and are voided with the manure. When the intestines are involved, the organisms also appear in the manure. From diseased kidneys or blad- der, they pass off in the urine, and from the udder, in the milk. Animals shedding organisms in this way are Agricultural Bacteriology. said to have "open" tuberculosis, and are a special menace to the remainder of the herd. "When the dis- ease is confined to parts of the body that have no exter- nal opening, as lymph glands, the cow is said to have 41 closed" tuberculosis. As long as the disease remains "closed," the animal is not a source of danger. It is impossible to foretell when the "closed" type will change to the "open," as it is certain to do sooner or later with the continued development of the disease. Hence every affected animal must be considered a menace, present or potential, to the herd and to the public health. Infection of the animal. The bacteria that come from diseased animals are carried into healthy animals in the dust from polluted mangers and dried manure. The dust may enter the lungs or it may lodge in the throat. The food may be soiled by the sputum of an animal, or by dust. The milk fed to calves and hogs may contain the bacteria, which then pass through the walls of the intestine into the lymph and blood streams and are carried to various parts of the body, especially the lungs and lymphatic glands. For this reason these are the organs most often affected. Hogs acquire the disease very readily when fed on contaminated milk, a single feeding of milk containing many tubercle bacilli suffices to infect hogs. Because of the content of manure in tubercle organisms, hogs running after cattle in the feed-lot are as likely to be diseased as those fed on skim milk. Animals may acquire the disease by contact with a diseased animal, as for instance by licking each other. Very rarely are the reproductive organs affected, and the calves from tuberculous dams are usually healthy. Because of this fact, it is possible to Tuberculosis. 115 raise healthy calves from diseased mothers, by what is known as the Bang system, which will be described later. Infection of the herd. The most frequent way in which the disease is introduced into a herd is by the purchase of a tuberculous animal. The larger the number of animals purchased, the more likely is the disease to be introduced. The animal purchased may appear healthy and may not at the moment be a source of danger, but is certain in time to become a center from which the disease will spread throughout the herd. As was stated, pure-bred herds are often diseased. All too often has a man introduced the disease into his herd through his efforts to improve his stock by the purchase of a pure-bred sire. The farmer should know the condition of every animal he buys. He will use great precaution to avoid buying an unsound horse, but the purchase of such an animal is not to be compared so far as probable future loss is concerned, to the purchase of a tuberculous cow, for the trouble from which the horse suffers is not likely to spread, while tuberculosis will surely infect others. Buy pure-bred animals from honest breeders whose herds are "known to be free from tuberculosis and from no others, even though they will guarantee the condition of the animals. The feeding of creamery skim milk and of whey is another- potent means of introducing the disease into the herd. The patron of a creamery or cheese factory carries to his calves and hogs a mixture of the milk of all the other patrons. In case there are tuberculous cows in any of the herds, the milk may contain tubercle bacilli. The farmer can protect his herd from such in- fection by the use of a farm separator, or by heating 116 Agricultural Bacteriology. the skim milk and whey to 160 F. before using. In Denmark and Germany such a treatment of skim milk and whey by the creameries and cheese factories is made compulsory. Some of the States have similar laws. It is a process to which no one should object. The butter and cheese maker will find himself repaid in the im- proved quality of the milk furnished him, since the milk cans are not polluted with injurious bacteria from dirty whey tanks. The farmer will find that the heated whey and milk will keep longer, hence will be sweet when fed. Spread of the disease in the herd. Any animal with open tuberculosis is giving off the tubercle bacilli, thus exposing the remainder of the herd to infection. The disease may spread slowly at first, but as> one animal after another becomes a new center from which the or- ganisms are furnished, the rate of spread increases. The rate of distribution is well shown in the following case: Twelve healthy animals were placed in a stable occupied by a diseased herd. In six months nine had become infected and the disease had made such headway that four did not pass inspection when slaughtered and examined by the Federal meat inspectors. The conditions obtaining in the barn with reference to light and ventilation will exert a great influence on the rate of dissemination in the herd. If the air is poor and the animals are forced to breathe it more* or less continuously during the winter, their ability to ward off the disease is reduced. Plenty of pure air is necessary for cattle as for man. The most important phase of the modern methods of curing tuberculosis in human beings is to live out of doors, to sleep out of doors, summer and winter. Light Tuberculosis. 117 has an injurious effect on bacteria, destroying them within a few moments when they are directly exposed to it. It has been shown by direct experiment that the disease will spread more rapidly in unsanitary barns, than in those which are well lighted and ventilated. The use of whitewash twice a year is advisable as it has a disinfecting action and makes the stable lighter. Symptoms of the disease. In the early stages there are no definite symptoms. The disease starts in some part of the body, usually in the lymph glands, and may make headway very slowly. For years it may be con- fined to a single gland, ,but sooner or later on account of some condition that may temporarily impair the re- sistance of the animal, such as calving, the disease develops more rapidly. In the last stages the animal becomes emaciated, the hair is rough, the eyes sunken, the head extended; the appetite may be good, but the food apparently has no effect. If the lungs are in- volved the animal may cough, especially when forced to move rapidly after resting. If there are hard painless swellings in the region of the throat or shoulders, the animal may be suspected of tuberculosis. If there are hard nodules in the udder; if one or more quarters are enlarged and hard, but painless and cold, or if the lymph glands at the top and rear of the hind quarters of the udder are enlarged, suspicion may be aroused. It is absolutely impossible for the most experienced veterinarian, in the great majority of cases, to tell from a physical examination alone, whether the animal has tuberculosis or not, or predict the stage of the disease. An animal may be the picture of health and be as great a source of danger as one in the last stages. 118 Agricultural Bacteriology. Tuberculin test. The only way by which it can be determined with certainty whether an animal has tuber- culosis or not is by the use of the tuberculin test. Tu- berculin is prepared in bacteriological laboratories by growing the tubercle organisms in beef broth containing glycerin. The organism produces a substance in the broth, which, when injected beneath the skin, has a peculiar effect on a diseased animal, causing a fever for a few hours; while in the healthy animal it has no appreciable effect. The beef broth is heated, and filtered FIG. 13. A TUBERCULOUS ANIMAL. A cow that has had the disease for five years. through porcelain, so that the tuberculin as used con- tains neither living or dead bacilli, but is simply an extract of their cells. It cannot produce the disease in healthy animals nor does it cause the disease to spread in affected animals. The test is made by taking a series of temperature- readings on the animal, injecting the tuberculin beneath Tuberculosis. the skin, and beginning ten hours later, a second series of temperature readings is taken. From a comparison of the temperatures before and after the injection of tuberculin, the condition of the individual animal is determined. Details of making the tuberculin test. The first series of temperatures must be taken in order to deter- FIG. 14. A TUBERCULOUS ANIMAL. An advanced case of generalized tuberculosis. Six weeks before the photograph was taken the ani- mal was in as fine condition as the one shown in Fig. 13. mine the normal temperature of the animal, since the temperature of the cow is not constant like that of man, but varies from hour to hour in the same animal and in different individuals. The average temperature of healthy milch cows ranges from 101 to 102 F. The temperature of fat stock and calves is higher ; of old and) 120 Agricultural Bacteriology. poor cows lower. The variation in the normal individual animal may range from 99 F. to 103 F. The varia- tion that may occur in the temperature of a well-kept healthy animal is shown in the following table in which are given the temperatures of two healthy cows for twenty-four hours, together with the rate of pulse and the number of respirations per minute. Exercise, ex- citement, and hot weather increase the temperature. A hot spell causes a rise of two and sometimes four degrees. The drinking of cold water lowers the temperature. Temperature, Rate of Pulse, and Respirations per Minute. Co\ r No. 1 Co iv No. 2 Tempera- ture Pulse Resp. Tempera- ture Pulse Resp. 10 A M 99 5F 66 18 98.6F 60 15 12 A M 100 8 54 15 99.4 54 15 2PM 101 6 48 15 100.2 54 18 4 P M 108 66 24 102.7 72 24 6 p M 103 1 57 18 103. 60 27 8 P M 103 56 16 102. 60 24 10P M 102. 60 20 102. 50 18 12 P M 102 5 56 ' 16 101 6 54 20 2A M... 102.4 64 18 102.2 58 18 4AM 102 2 54 24 101.5 60 24 6 A M 101.8 60 18 102.2 60 20 8 A. M 102.5 56 16 103.2 60 18 The temperature is taken in the rectum by means of a clinical or fever thermometer, similar to those used by physicians. The mercury in these thermometers cloes not run down, but stays at the highest point reached, i. e., registers, until shaken down. Veterinary ther- mometers of heavy glass with a ring at the end are best ; a string is attached to the ring and to a small paper clamp. When the thermometer is inserted in the animal, the clamp is attached to the long hair at the base of the tail. In this way the thermometer, if ejected by the animal, will not be lost or broken on the floor. Tuberculosis. 121 The mercury should always be shaken down below 98 F. before the thermometer is inserted. If the animal objects to the insertion, scratching her back with a card will attract her attention and no difficulty be met. Vaseline may be used on the instrument to aid in its insertion. The temperature should be taken four times at inter- vals of. 2 hours, before the injection of the tuberculin. The injection of the tuberculin is made by the use of a well-made hypodermic syringe. The injection is made usually back of the shoulder blade, but may be made wherever the skin is loose and thin. The needle is thrust through the skin at right angles, but care should be taken not to push it into the muscular tissue below. A syringe with a needle that slips on, rather than one that screws on to the barrel is preferable, since the needle can be inserted and the syringe then attached. The needle should be of 15 or 17 wire guage; strong needles are needed for this kind of work. It is well to sterilize the syringe before using by placing it in a pan of cold water and bringing the water to a boil. Animals whose temperatures are abnormal, say 103 P.. should not be injected, neither is the test as reliable when applied to animals about to calve, or those in neat or to young calves less than 3 months old. The dose of tuberculin depends upon the size of the animal. That distributed under the auspices of the United States Department of Agriculture is diluted, ready for use and requires 2 c c. (40 drops) per 1000 pounds live weight. The amount of the commercial tuberculin to be used is always stated on the package. The temperature records are commenced 8 to 10 hours after the injection, which is usually made in the evening. 122 Agricultural Bacteriology. The taking of temperatures should be continued at least until 18 hours after inoculation" or until there is a per- manent decline toward the normal. The animals should be kept in as normal a condition as possible during the test. Care should be taken not to excite them as this will cause the temperature to rise. It is usually preferable to make the test at the time the cattle are kept in the stable, e. g., fall or winter. One point to which attention should be especially directed is the watering of the animals during the test. If an Hours After Injection. 10 12 14 16 18 20 107 106 105 I04 C 3/ FIG. 15. TEMPERATURE CURVES. 1. the temperature curve of a healthy animal after injection with tuberculin; 2 and 3. the tempera- ture curves of "tuberculous animals after injec- tion with tuberculin. (After Moore.) animal drinks large amounts of cold water its tempera- ture is often lowered 2 to 3 F. If the depression of temperature should come during the reaction fever, it might lead to a misinterpretation of the results. Water should be given during the test, and no trouble will ensue if given in small quantities. The increase in temperature in the tuberculous animal is usually a number of degrees. In the case of a positive Tuberculosis. 123 reaction the temperature begins to rise 10-14 hours after injection, reaches a maximum in 12-14 hours and then declines rapidly. The maximum temperature may reach 105 to 107 F., e. g., 3 to 5 F. above the average normal. An animal is said to have reacted and is looked upon as diseased when the maximum temperature after injection is 2 or more above the average normal tem- perature before injection, or is 1.5 F. above the highest temperature taken before injection. The reaction fever is often so slight that one cannot decide positively from this alone whether the animal is to be adjudged dis- eased or not. In the interpretation of such cases a full knowledge of the conditions surrounding the test, and a history of the animal is of much value. If many other animals of the herd have reacted, a less rise in the case of one or more animals would be classed as a reaction, when it would not be in case no other animals had shown any signs of a reaction. Suspicious animals should be retested with a larger dose (3 fold) after a period of 60 days. Animals once tested will not give a proper reaction upon retest if tested within a short time after the first injection. Sufficient time must elapse to permit elimination of the first tuberculin. Animals in the last stages of the dis- ease often do not react. The disease in such animals can usually be diagnosed by a physical examination. During the incubation period of the disease before any diseased tissue has developed, animals do not react to tuberculin. The purely mechanical part of the test can be carried out by any intelligent farmer capable of reading ac- curately a clinical thermometer. The interpretation of the test should, however, be made only by an experienced 124 Agricultural Bacteriology. person. No farmer should fail to test his herd because a veterinarian is not to be obtained or because of the expense of employing one. The tuberculin can be pur- chased of reputable firms at a cost of 15 to 25 cents per dose. The instruments need not cost over five dollars. The work can be done during the times when the farm work is least pressing. The advantage of being able. to test one's own animals is very great, since retests can be made on suspicious animals and animals to be brought into the herd, tested. If some one must be employed to make those tests at ir- regular times, the testing is likely to be neglected and because of this neglect, the farmer may fail to free his herd from the disease or may introduce it by the pur- chase of a cow supposed to be healthy. Reasons for testing the herd. Every farmer should determine the condition of his herd for its own sake because delay means increased loss through diminished production of diseased animals, through further spread of the disease in the herds, and through death of animals before the normal time. From the standpoint of duty to himself and to society, he should see that his herd is healthy. This can be, done only by the use of the tuber- culin test. Some states have passed laws requiring compulsory testing, and for animals found affected, partial remuner- ation is given. The methods of disposal of reacting animals depends upon the state of the disease. When the carcass is affected only slightly, it is passed for food under Federal inspection. If the disease shows evidence of being generalized, the carcass is condemned and tanked for fertilizer. As previously indicated, it is possible to raise healthy Tuberculosis. 125 calves from diseased mothers. With valuable breeding stock, the loss caused by immediate slaughter would be too great. The herd may be separated into the affected or reacting, and the healthy. The two herds should be kept in separate barns and pastures; the calves of the diseased animals should be removed at birth and fed on the milk of healthy animals or on the milk of the dis- eased animals which has been heated to at least 160 F. so as to destroy any tubercle organisms it may contain. It has been shown many times in Denmark and in this country that by this method a diseased herd can be put on a healthy basis within a few years and at very slight expense. Any farmer who wishes to employ this system should apply to the state authorities connected with the control of contagious diseases of animals for more de- tailed advice. There is no successful practical means at present of protecting cattle against tuberculosis by vaccination. Certain methods have been widely adver- tised as efficient, but are not a practical success. Tuberculosis of swine. Hogs acquire the disease very easily by the ingestion of contaminated food, such as skim milk, butter-milk, slime from cream separators, or from cattle in feed lots. The parts of the body most often affected are the glands of the head, neck, and in- testines. The liver may show large rounded nodules, yellowish-white in color, or minute nodules in great numbers. The spleen often shows large nodules and the lungs many small ones. Since the larger number of hogs are sent to market be- fore they are a year old, the disease does not usually make such headway as to cause any visible symptoms. The tuberculin test has been used in the case of hogs, but it is much more difficult to apply than with cattle. 126 Agricultural Bacteriology. The temperature of the hog is much more variable than that of the cow. During the test the animal must be kept perfectly quiet, which can be done only by placing it in a narrow crate so that movement is impossible. Tuberculosis of fowls. The disease in chickens and other barnyard fowl is due to a different variety of the tubercle bacillus than that causing the disease in cattle -and man. It has caused great loss in many flocks. The most important symptoms are emaciation, although the appetite is good. The eyes are bright, until shortly be- fore death, although the fowl may be weak and move about but little. The birds are often lame due to the disease in the joints. Of the internal organs the liver is most affected. At first it shows small, grayish points, later, yellow patches appear. Differential diagnosis. There are some diseases of cattle and sheep that are often mistaken for tuberculosis, especially those in which nodules are produced in the walls of the intestines by animal parasites. Sheep are affected with an intestinal disease known as " nodular disease" which to the uninitiated might -be thought to l)e tuberculosis, but which is really caused by a parasitic worm which burrows in the wall of the intestine forming :a greenish colored nodule about the size of a pea. CHAPTER XII. GLANDERS AND TETANUS. Glanders is one of the important diseases of the horse. It appears in two forms, the one type affecting the mucous membranes being called glanders, while that which affects the lymphatic system of the skin is called farcy. The disease is primarily one affecting horses, mules, and asses, but dogs and cats may acquire it by eating glandered meat. Man may also be affected, gen- erally acquiring the disease from horses. It is an es- pecially fatal trouble in man. Distribution of the disease. Glanders is found in nearly all parts of the world. Australia is said to be free from it. The congregation and transportation of large numbers of horses, as is necessary in war opera- tions has been instrumental in spreading the disease widely through the world. During and after the civil war its distribution was very rapid in this country due to the sale of horses and mules by the government. In the Mexican war, it was introduced into Mexico by the American cavalry. The disease is more often found in large stables than on the farm. In lumber camps, on the ranges, and in the cities, it is constantly present. Farmers who buy animals from such places are likely to bring the disease onto the farm. There are certain conditions that pre- dispose the animal to the trouble such as unsanitary surroundings in the stable and overwork. A horse may be in good flesh and be able to stand work and yet have the disease in a chronic form for 128 Agricultural Bacteriology. years. It is through the purchase of such an animal as this that the disease is brought onto the farm, such animals also serving to spread the trouble through the infection of mangers and watering troughs. FIG. 1 6. GLANDERS. Sores formed by the breaking of the farcy buds. Note the swollen condition of the leg. (After Reynolds.) Symptoms of the disease. The acute form of the dis- ease is rare in the horse but common in the mule and ass. In the chronic form the development is usually slow and insidious. There is generally a -discharge of Glanders and Tetanus. 129 a sticky fluid sometimes streaked with blood from one or both nostrils. The animal may be lame and may cough. In glanders of the skin (farcy) nodules which are called farcy buds are found in the skin and in the adjacent tissue. They vary in size from that of a hemp- seed to that of an egg. These nodules break and form running sores on the surface of the body, the discharge being yellowish and sticky. The nodules usually appear on the legs and on the head. The sores often heal but leave a permanent scar. Tissues affected by the disease. In chronic glanders the changes in the tissues are found in the air passages, the lungs, lymph glands and skin. Small nodules may form on the upper part of the septum of the nose. The nodules, which are translucent and grayish in color, may break and form ulcers which destroy the surrounding tissue to a greater or less extent, a perforation in the bony nasal partition may even be produced. There are found in the lower air passages and in the lungs nodules resembling very much those of tuberculosis. They are pearl-gray in color, usually have a yellowish spot in the center due to the death of the tissue. The nodules are found both on the surface of the lung and in the lung tissue. Similar nodules are also found in the spleen and less often in the liver and kidneys. Care should be exercised in the handling of suspected horses as the disease is easily transmitted to man. The symptoms in the human being are much the same as in the horse, sores forming on the hands and in the eyes and nose. Death usually takes place in two to four weeks although the disease may become chronic. Treat- ment is of little avail. 130 Agricultural Bacteriology. Mallein test. Glanders can often be recognized by a physical examination on account of the characteristic sores in the nose. The horse is subject to nasal diseases that may be mistaken for glanders. When the disease can not be diagnosed by the physical examination, re- course may be had to the mallein test which is similar to the tuberculin test. Mallein is prepared in the same manner as is tuber- culin by growing the glanders bacillus in glycerin broth. The manner of applying the test is also similar to the method followed in the tuberculin test. The mallein is injected beneath the skin and a series of temperatures taken both before and after the injection is made. A few hours after the injection of the mallein there appears at the point of inoculation, a hot inflammatory swelling, which in a glandered horse is very painful, and con- tinues to increase in size for twenty-four to thirty-six hours. This persists for several days, gradually disap- pearing in eight to ten days. With healthy horses a small swelling is produced at the point of inoculation but it disappears in twenty-four hours. At the time the swelling appears the diseased animal is dull, breathes rapidly and has a poor appetite. In healthy horses no such effect is noted. In the affected animal a rise in temperature, from 2 to 2.5 F., occurs in the course of eight hours, reaching its maximum in ten to fifteen hours. The high temperature persists for twen- ty-four to forty-eight hours instead of only a few hours as in the tuberculin test. In healthy horses there is no rise in temperature. The test is not quite so reliable as the tuberculin test for some diseased animals do not react to the mallein test. Any animal that reacts to the test is certain to have glanders. Glanders and Tetanus. 131 In most of the states glandered horses are destroyed by the health authorities whenever they are detected. The farmer should protect his horses against glanders by not allowing them to come in contact with strange horses, especially if there is any reason to believe that the animals may be affected. If an animal is purchased from a sale-stable or from a range, it is well not to bring it in contact with the farm horses, until it is certain that it is not affected with the chronic type of the dis- ease. The use of the public watering trough and public stables is often a means of infecting a healthy animal. A stable in which a diseased horse has been kept should be disinfected. The glanders organism does not form spores, hence is easily killed. TETANUS. Tetanus or lockjaw as it is often called, is a disease that appears most often in the horse and mule. It may however affect any of the domestic animals and also man. Tetanus occurs in all parts of the world, most frequently in the warmer regions. The organism causing the disease is an anaerobic one, the real home of which is in the soil. The disease is not a directly contagious one, i. e., one animal does not acquire it from another. The infection takes place through a wound, especially one into which dirt is carried. A wound which bleeds freely is less dangerous than one that does not as the organisms are likely to be washed out. A contused lacerated wound is especially dangerous as the opportunity for admission of dirt is increased. Wounds caused by rusty and dirty nails are often a way in which the bacteria are introduced into the body. The disease may follow an operation, such as 132 Agricultural Bacteriology. the docking of horses, the castration of colts, and through the infection of the umbilical cord of colts. Symptoms. The organism grows only at the point of introduction. It produces one of the most powerful poisons known. This is absorbed and is carried to all parts of the body and its action on the nerves causes the characteristic symptoms, of spasms in various mus- cles. The muscles of the throat and jaw are often paralyzed, giving rise to the common name of the dis- ease, lockjaw. The muscles of the neck may be in- volved, causing the head to be held in a stiff outstretched manner. Those of the back and tail are also affected. On post-mortem examination no marked lesions are found. The disease is usually fatal in sheep and in hogs ; about 75 per cent of the horses affected die. The dura- tion of the disease in the horse may be but a few days or it may continue for several weeks. Preventive measures. A preventive and to some ex- tent a curative treatment has been developed in the tetanus antitoxin. This antitoxin is prepared in the same manner as that used for the prevention and cure of diphtheria. A horse is injected with a small amount of the filtrate of a culture of the tetanus organism in broth. This contains the same poison that the organism produces in the body of the animal. A very small dose must be given at first. The horse soon recovers from the effect of the injection and a larger dose is then given. The treatment is continued for some time with larger and larger doses of the poison. Meanwhile the animal is producing a substance in its body to counteract the poison that has been given it. This process of forming the antitoxin does not cease when enough has been made to neutralize the amount of poison given, but an excess Glanders and Tetanus. 133 is made and is found in the blood of the animal. If some of the blood can be carried to an animal that has just begun to show symptoms of tetanus, the antitoxin contained in it will neutralize the poison that is being formed and thus tide over the time until the suffering animal can make its own antitoxin. This transfer of the protecting substance is done by drawing a quantity of blood from the immunized animal, allowing it to clot and collecting the serum which comprises the commercial product. The antitoxin is used in the treatment of both horses and man. In order to protect an animal against the infection that may occur during an operation a small dose is often given before the operation. In vaccination, where a mild form of the specific disease is always pro- duced, the protection lasts for some time. The protec- tion afforded by antitoxin endures for only a short time. A large proportion of the disease in human beings is the result of wounds produced by Fourth of July ac- cidents. The filling in many forms of fire works is earth. This may contain tetanus bacilli which will be blown into the skin by a premature explosion of a fire cracker or other form of fire works. CHAPTER XIII. RABIES. Rabies, or hydrophobia, as it is frequently called, is a disease especially affecting dogs. Practically all of the domestic animals and many wild animals may, how- ever, contract the disease. Man is also susceptible. While the disease is especially important on account of its communicability to man, it is becoming of much economic importance to the farmer through the loss of stock infected by the- bites of rabid dogs So far as is known the disease is transmitted from one animal to another or from animals to man only through the bite of a rabid animal. The tendency of the dog to bite is the explanation for the great preva- lence of the disease in this animal. The organism caus- ing the disease has never been discovered. Certain structures have beenx found in parts of the body that are supposed to be the real cause, although the relation has never been thoroughly established. Distribution. The disease is found in nearly all parts of the world. Australia is said to be free from it. This freedom is due to the rigid enforcement of quarantine laws in regard to the importation of dogs. England through strict regulations concerning the muzzling of dogs and through her quarantine laws has practically succeeded in stamping out the disease. In our own country rabies is found in every state. In some sections Rabies. 135 it is very prevalent while in others it is rare. It is un- doubtedly on the increase in many sections. This is due to the lack of regulations in regard to the muzzling of dogs. Many people believe that the muzzling is an inhumane practice, while still others assert that rabies is a myth and has no existence except in the minds of the doctors. So long as such ideas are held, rabies will continue to exist. There is probably no other disease with which there is connected so many popular fallacies as with rabies. It is currently believed that it occurs only during that part of the summer known as "dog days." In reality the disease is as prevalent in winter as in summer and if it is desirable to muzzle dogs in July and in August, it is also desirable to muzzle them at all times. Period of incubation. The period of incubation of rabies is about forty days in man, in the horse from twenty-eight to fifty-six days, in the dog from twenty- one to forty days. The period of incubation, however, may vary widely from these averages as it will depend on the location and severity of the bite. The part of the body in which the organism seems to grow is the nervous system. The symptoms of the disease are not ap- parent until the brain is affected. The time required for the organism to reach the brain depends on the distance of the bite from the brain, thus the symptoms appear more quickly when the bite is on the face than when it is on the limbs. The length of the period of incubation is also dependent on the severity of the bite. Where a slight wound is inflicted, the symptoms will not as a rule follow so soon as if several wounds had been made. Symptoms. Two forms of the disease are known, the dumb, and the furious type, so called on account of the- 136 Agricultural Bacteriology. nature of the symptoms noted. In the rabbit the dumb type is most usual ; in the dog it is very rare. The symp- toms of rabies appear slowly. With the furious type of the disease, the animal is usually more nervous than nor- mal and more affectionate, or it may be dull and try to avoid people. The nervousness increases until the ani- mal is unable to rest. It may become delirious and snap at the air. The itching of the tissue at the point of in- oculation causes the dog to lick the wound or even to bite itself. The nervousness may be so great that the dog leaves home, and starts on a wandering trip which may last for several days, usually returning home in an ex- hausted condition. During this absence from home is the time of greatest danger, for the dog then comes in con- tact with other animals. The rabid dog does not go out of its way to bite, as is frequently stated, but any object or other animal that is in its way is very likely to be snapped at. The animal that is most usually bitten is another dog. In this way the disease is spread, as on such a trip the mad dog may infect a large number of dogs. The animal may die while away from home. More often it reaches home in a pitiable condition, and often the owner may be bitten in seeking to relieve the animal. The greatest care should be exercised in handling any dog suspected of rabies. As the disease progresses, cer- tain parts of the body become paralyzed, the muscles of the throat generally being the first to be affected. This has led to another popular fallacy, namely that a rabid animal has a great fear of water, often going into fits at the sight of water. This fallacy has given to the disease the name ''hydrophobia," meaning fear of water. The .animal is unable to swallow, and in making an attempt Rabies. 137 to do so is often thrown into convulsions. The animal will take water as long as it is able to swallow anything. The paralysis gradually extends and death usually takes place in four or five days after the first symptoms are noted. In the dumb type the nervousness is not present, the first symptom is usually paralysis of the muscles of the throat. This often leads the owner to think the dog is choking and an effort may be made to remove the sus- pected object by inserting the hand into the mouth. This is a very dangerous thing to do for the saliva is in- fectious and if the hand should be scratched in the operation there is danger that rabies may develop. Even the licking of the hand by a rabid animal may serve to infect a person if there is any sore or abrasion of the skin. The extent of the danger from bites depends to a large degree upon the location of the bite. If the teeth of the dog pass through the clothing, the saliva, which carries the virus, will, generally, be wiped off. The disease will be far less likely to follow than if the bite is on an un- protected part as the face or hands. In like manner a long-haired dog is more protected than a short-haired one. As previously stated the danger also depends upon the severity of the bites. People bitten by rabid wolves more often develop the disease than those bitten by dogs because the bites are likely to be more extensive. An- other fallacy connected with rabies is that if persons or animals are bitten by any dog, they are likely to become rabid should thejiog contract the disease at any future time. There is, of course, absolutely no foundation for this impression, for the disease is transmitted only by an animal that is diseased at the time the wound is in- flicted. 138 Agricultural Bacteriology. The body of a dog that has died of rabies shows no marked changes on post-mortem examination. The stom- ach is likely to contain foreign objects, such as grass, sticks, etc. Treatment of rabies. If the disease develops until symptoms are apparent, nothing can be done and death is certain to follow. In human beings the death is one of the most horrible than can be imagined. However, if treatment is begun early enough the disease can be pre- vented. The basis of the treatment is exactly the same as in the cases of anthrax and black leg. A weakened form of the virus is used. If rabbits are inoculated with a portion of the spinal cord or brain of a rabid animal,, they will usually die from the disease in fifteen to twenty days. If repeated inoculations are made from one ani- mal to another, the virulence of the causal organism in- creases ,until the rabbits will die in six or seven days. The virulence can not be farther increased and the virus is said to have a fixed strength. The spinal cord of a rabbit that has died after inoculation with such a fixed virus is removed and placed in a dry atmosphere, the re- sulting desiccation weakens the organism gradually. A person applying for treatment is given a sub-cutaneous inoculation with a suspension in water of a cord that has been dried for fourteen days; on the following day the inoculation is made with a cord that has been dried for a shorter period of time. Within a week or ten days the inoculation is made with a cord that has just been re- moved from the animal, and which, of course, contains the unweakened virus. The treatment, which was dis- covered by the French bacteriologist, Pasteur, has re- sulted in the saving of hundred of lives and has robbed the disease of many of its terrors. The treatment is em- Rabies. 139 ployed only with human beings, although animals could be treated but the expense is too great. It is noteworthy that the protective treatment can be applied in the case of rabies several days after the bite is inflicted, an unusual condition with reference to im- munization. On account of the time and expense con- nected with the preventive treatment, it is desirable to know with certainty that the suspected animal really has rabies. This can be determined with certainty only by keeping the dog that inflicted the bite under observation. If the animal is rabid, a definite diagonsis can be made from the symptoms, and death is certain to follow. If the dog has bitten persons, it is especially desirable that it should not be killed for the delay in determining whether the animal was actually rabid or not may be sufficient to allow the disease to make such headway that treatment will be of no value in preventing the disease. Until re- cently the diagnosis was made by the inoculation of a portion of the spinal cord into rabbits. A more rapid method is now employed, a definite portion of the brain is examined microscopically and within twenty-four hours the diagnosis can be made, while with the old method at least two weeks were required. A very unsatisfactory condition in all methods of diag- nosis in the laboratory exists. If the rabbits inoculated succumb to rabies or if the peculiar bodies characteristic of the disease are found in the brain of the suspected animal, it is certain that rabies is present. If the bodies are not found, it is not certain that the animal was free from the disease. Again, the rabbits inoculated may not die from the disease for a much longer period than the average, so late, indeed, that preventive treatment may be of no value, if it is not begun until the diagnosis is 140 Agricultural Bacteriology. made by means of animal inoculation. These things -emphasize the importance of not killing the suspected animal, but to secure it, and watch the progress of the disease. If rabies is present the animal is certain to die with well marked symptoms which can not be mistaken. If the dog is suffering from various other troubles that cause it to be nervous, or if it has inflicted the bite through provocation, an entirely different history will result. Every effort should be made to secure the dog that has bitten other dogs, animals, or persons. If the suspected dog has been killed, the head should be re- moved and sent to a laboratory for examination ; most of the laboratories connected with the state boards of health are equipped for such work. Care should be taken not to injure the brain else diagnosis may be impossible. The wounds made by a suspected animal should be cauterized immediately to destroy the virus possibly pres- ent. This can be done by the use of strong carbolic or nitric acid or, if neither of these are available, by the use of a hot iron. Only about sixteen per cent of people bitten by rabid animals develop rabies and this is greatly reduced when the wounds are properly treated. The preventive treatment is given in Pasteur Institutes which have been established in the various cities. Some of the states have such institutes in connection with the laboratories of the boards of health. Recently farther improvement has been developed so that the vaccine can be sent by mail to the resident physician, who admin- isters it. In this way a person can take the treatment at home and at much less expense than formerly. Rabies in other animals. Next to dogs, cattle seem to be most frequently affected, probably because rabid dogs have more opportunity to bite them than any other Rabies. 141 domestic animal except other dogs. Cattle are most fre- quently bitten on the hind legs, hips and lower jaw. About twenty-five to thirty per cent of those bitten de- velop the disease. The symptoms are very similar to those described in the dog. The furious type is more common than the dumb. The first symptoms are loss of appetite, of rumination and of milk secretion. Increased nervousness is shown by the bellowing, pawing, and a tendency to attack other animals. On account of the in- creased amount of saliva, there is a constant frothing at the mouth. The animal becomes stiff and unsteady in its gait. The temperature is not above normal. Death results from paralysis. Quite similar symptoms may be noted in other dis- eases in which the brain is affected as for example in lock jaw, anthrax, and spinal meningitis. Horses, sheep and hogs are often bitten by rabid dogs. The symptoms are usually those of the furious type of the disease. A rabid horse or hog may bite other animals or man and cause the spread of the disease. CHAPTER XIV. ACTINOMYCOSIS, GARGET, COWPOX, AND CON- TAGIOUS ABORTION. Actinomycosis or lumpy jaw as it is commonly called, is a disease of cattle although horses, sheep, hogs, and dogs may be affected. Man is also subject to the disease. The cause of the disease is not one of the bacteria but an organism much like a mold. The disease is not a highly important one as only about one out of sixteen hundred .animals are affected with it. Tuberculosis is at least fifty times as prevalent as is actinomycosis and yet in many places the latter disease has made more of an im- pression on the popular mind than has tuberculosis. The reason is that the changes which tuberculosis pro- duces are hidden, while those of actinomycosis are usually evident on the surface of the body in the form of a lump on the jaw. Animals rarely die of the disease. Actinomycosis is not a contagious disease since one animal does not acquire the disease from another. The organism that causes the trouble is supposed to grow on barley and other grains. It enters the body through a wound in the mouth, through a hollow tooth or it may "be inhaled. Symptoms. The first symptom is a slight swelling in the region of the head or throat. The swelling gradually increases in size and is hard and dense. It may break and discharge a thick yellow pus. The opening may heal temporarily only to break later and discharge again. Actinomycosis. 143 The discharge may be on the outside or into the mouth or throat. The sore at the point of discharge may be- come very large and have the appearance of a head of cauliflower. The growth of the tumor may continue for years, death being caused because of its interference with breathing or swallowing. The tongue is sometimes in- volved, in which case the disease is often given the name PIG. 17. ACTINOMYCOSIS. 'The spongy condition of the jaw bone was produced by the growth of the fungus. of "wooden tongue." The organism may invade the bony part of the jaw, causing the bone to become spongy and enlarged, while the teeth may fall out. Lesions. The lesions of actinomycosis may occur in various other parts of the body than about the head. In the lungs nodules are often formed that are very similar to the nodules found in tuberculosis of the lungs. They vary in size from mere specks to that of a pea. Still other organs, as the spleen, liver, and udder may contain the nodules produced by the growth of the organism. The pus discharged from the actinomycotic nodules i* 144 Agricultural Bacteriology. yellowish and contains minute yellow granules, often called sulphur grains. These are masses of the causal organism. Treatment. The disease is one that yields quite read- ily to treatment. The most successful remedy is potas- sium iodide which is given in water as a drench. The dose is from 1.5 to 2.5 drams per day. The treatment can not be maintained continuously for a long time as the drug affects the animal unfavorably, causing the eyes to run, the skin to become dry and rough, and a loss of appetite. "When these troubles manifest themselves the medicine must be stopped for a few days and then begun again. Three to six weeks are required to effect a cure. All animals do not respond to this treatment. Iodine should never be given to milch cows as it is given off in the milk. It also decreases the flow of milk or may stop it entirely. It is also likely to cause abortion. Man does not acquire the disease directly from cattle but is infected in the same manner as are cattle through wounds in the mouth. The meat of animals that have the disease in a localized form is fit for human food and is passed by the inspectors in the slaughter-houses. GARGET. Inflammation of the udder is known by various names as garget, mastitis or mammitis. The trouble is charac- terized by the production of a fever and a swelling of the gland with more or less change in the nature of the milk. Catching cold in the udder or an injury are often responsible for the trouble. Animals differ widely in their susceptibility to udder troubles. With some, lying on a cold concrete floor is sufficient to cause trouble. An injury serves to introduce some of the bacteria of the skin Garget. 145 or of the milk ducts into the udder tissue where they cause inflammation. Such physiological troubles are usually confined to a single animal, and the swelling and fever are generally temporary. In well developed cases the milk is likely to contain flakes of slimy clotted ma- terial. If the inflammation persists, the milk secretion may cease altogether and only a yellowish liquid be ob- tained. If the attack is of short duration, no permanent harm is likely to result, the normal flow of the diseased quarter may be restored during the same lactation period or at the beginning of the next. A prolonged attack is likely to cause a loss of the quarters involved. A much more serious type of garget is that known as infectious or contagious garget, which is caused by cer- tain bacteria which are able to grow in the udder and cause serious trouble. This form is much more import- ant than that caused by cold or wounds as it is very likely to spread from one animal to another. The milker is usually the cause of the spread of the trouble in the herd. An animal that has garget in any form should be milked last or the hands should be washed in a disinfectant such as can easily be made by the use of the corrosive sublimate tablets that can be obtained at any drug store. It is also advisable to remove the animal from the stable. Through carelessness a large part of the herd may be- come infected. The milk from animals having inflammation of the udder, no matter how slight it may be, should not be mixed with that from healthy animals. It should be thrown away. 146 Agricultural Bacteriology. COWPOX. Small pox in man finds its counterpart in diseases of similar nature in the cow, horse, and sheep. There is ap- parently some relation existing between human small pox and cow pox, as inoculations from man to the cow and from cow to man can be made. The disease in sheep is limited to sheep alone, not even being transmitted to goats. The lesions of cow pox appear on the udder and teats. The first symptom is a tenderness of the skin, followed by the appearance of small reddish spots, which develop into vesicles or blisters filled with a clear liquid. Later ( tho contents become more like pus. The pustules be- come darker in color and drier until nothing remains but a dry scab that drops off. The duration of the disease is about twenty days. It is not a serious disease as far as the herd is con- cerned. With milch cows it may cause a great deal of inconvenience in milking. The vesicles are broken by the hand of the milker, thus producing large sores on the teats which heal slowly and which make milking very difficult. An effort should be made to limit the spread of the trouble in the 'herd by milking the affected cows last, since one of the agents of distribution of the dis- ease in the herd is the milker whose hands are contam- inated from the ruptured vesicles. Nothing can be done in a curative way, but the use of carbolized vaseline on the teats may serve to make the milking less difficult and aid in healing the sores. The milker may become infected from the cow by get- ting some of the contents of the vesicles into a wound or crack on the hand. The trouble in man is local and not at all serious unless the sores become infected with pus- Contagious Abortion. 147 forming bacteria. An attack of cow pox protects the individual against small pox. In fact the beginning of modern vaccination against small pox was due to an ob- servation made by Jenner that people that became in- fected with cow pox did not acquire small pox. Vaccine, which is used as a preventive against small pox, is made by inoculating calves with the virus of cow pox. To make the vaccine the scabs, that form, are removed and ground with glycerine. All the processes are carried out with the greatest care in order to avoid the contamina- tion of the vaccine with organisms that might be injur- ious to the persons vaccinated. CONTAGIOUS ABORTION. The causes of abortion in cattle may be divided into three classes: (1) abortion caused by mechanical injury or as the result of some other disease, (2) abortion due to the presence of large amounts of smut in the feed, (3) abortion due to the infection of the animal with a spe- cific organism. The first two classes are of interest to us only as they are to be differentiated from the true con- tagious abortion. The cases of abortion belonging in the first class are sporadic and are caused by some injury, such as slipping, falling, being hooked, jammed or kicked. The cases occur singly and no connection be- tween the cases can be traced. Ergot or smut of corn and other plants when ingested has such an effect on the uterus as to cause the expulsion of the fetus. If the cause is of this nature a large num- ber of cases of abortion are likely to occur within a short time since all the cattle are under the same conditions. With a change of feed the trouble disappears. Some 148 Agricultural Bacteriology. plants to which cattle may have access in the pasture have a like effect on the pregnant animal. Contagious abortion or that caused by micro-organisms is more prevalent and more important, since one infected animal introduced into the herd may serve to infect the entire herd. Cause. The organism responsible for the trouble is not known with certainty. The disease is undoubtedly most often brought into the herd through the purchase of an infected animal. Once introduced it spreads from one animal to another in various ways. The first case in the herd is not likely to attract attention and hence op- portunity is offered for further spread. Much would be gained if every case of abortion in the herd were treated as though it were contagious. The disease usually disap- pears from a herd in two or three years, in case no new- animals are brought into the herd or young animals do not serve to perpetuate the disease. This has been sup- posed to indicate that an animal becomes immune after two or three consecutive abortions. The abortion usually occurs between the fifth and eighth months of the period of gestation. Symptoms. Shortly before the time for the fetus to be expelled, symptoms are shown in varying degree by different animals. The vulva and surrounding tissue is swollen and a yellowish discharge is noted. The udder increases in size. Within two to three days delivery occurs, which is usually accomplished without trouble. If the abortion occurs during the eighth month of preg- nancy, the milk flow will usually be quite normal, at earlier periods the animal gives milk but a short time. Contagious Abortion. 149 Infection of the animal. There are many ways in which the causal organisms may be carried from the in- fected animal to a healthy one, as by direct contact, soiled bedding, the attendants, etc. A less direct way is by the bull that has served infected animals and later has been used with healthy cows. The bull is one of the means of introducing the disease into the herd, either through purchase or by the use of the bull of the herd on in- fected cows or by patronizing bulls kept for public ser- vice. Prevention. Attention should be directed to the con- dition of the herd from which each animal is purchased. If it is not certain that the herd is free from the disease, it may be well to keep the purchased animals apart from the herd until after calving at full time has occurred. In order to prevent the spread of the disease in the herd attention must be directed toward the destruction of all material that may contain the organisms. To accom- plish this, the fetus and after-birth should be destroyed, preferably by burning. The aborting animal should be removed from the herd, the stable disinfected and all cows that may have been exposed also disinfected. The animal should be given vaginal douches with some disin- fecting solution such as one ounce of tincture of iodine in one ounce of glycerine, the mixture being added to one gallon of warm water. The external genitals, hind quar- ters, and tail should be washed with a one to one thou- sand solution of corrosive sublimate. The douches and external treatment should be repeated several times and the animal should not be returned to the herd as long as there is any vaginal discharge. All pregnant cows of the herd should be treated by washing the external genital parts with corrosive subli- 150 Agricultural Bacteriology. mate and the vagina should be cleansed with a suitable antiseptic solution. The bull may be treated by wash- ing the external parts of the sheath and the abdomen with soap and water and then with a one to one thousand solution of corrosive sublimate. The sheath may be in- jected with a one per cent solution of carbolic acid. The disinfection of the stable should be done as de- scribed in a subsequent chapter. It rests largely with the owner as to whether the disease persists or not. The measures necessary to prevent the spread of the trouble in the herd may be burdensome and are very likely to be neglected. It is very certain that the various methods of treatment widely advertised rely for their effective- ness upon such means as the farmer can apply for him- self. CHAPTER XV. DISEASES OF HOGS. The hog may be affected by a number of the diseases that have already been treated, such as tuberculosis. By far the most important disease that especially affects the hog is hog cholera. It is probable that there are two and possibly three diseases, caused by different kinds of organisms to which this term is usually applied. The veterinarians have called one of these diseases hog cholera, another swine plague, and within recent years y it has been found that there is still a third kind of or- ganism which causes trouble in the hog. These diseases may be discussed together since methods of prevention are identical. The knowledge of no other important group of dis- eases of the domestic animals is in such an unsatisfac- tory condition as that concerning the diseases of the hog. This is true both with reference to he causal or- ganisms, and to methods of prevention by means of vac- cine or serums. Until very recently no progress had been made in methods of fighting the diseases of the hog for twenty years. ; Distribution. Hog cholera is supposed to have been imported to this country in the hogs introduced from Europe. The first outbreak of which record is had was in Ohio in 1833. Since that time it has spread to every state. In the great corn growing states it causes greater annual losses than any other disease of the domestic ani- 152 Agricultural Bacteriology. mals. It is found in England, Germany, and other European countries. Symptoms. The hog when ill usually shows much the same symptoms, whatever the trouble may be. The disease develops from seven to fourteen days after in- fection occurs. When the disease appears in a herd, some of the animals are certain to die after a short ill- ness of a few hours, or at longest a few days, of acute cholera. Others show signs of illness for a much longer period and some recover. The animal acts dumpish, and tries to hide. The appetite usually is very good. The skin of the ears, nose, abdomen, and inside of the thighs is reddened. "With chronic cases weakness of the limbs, especially the hind legs, develops and the animal moves with difficulty. Post-mortem examinations. The disease often can- not be diagnosed with certainty from the symptoms, but an examination of the carcass is necessary. In the acute type one of the most common and striking changes is in the spleen. This organ is often much enlarged, soft and very full of blood. Hemorrhages are found in various parts of the body, especially on the lining of the abdomen and chest, and on the inner wall of the intestine. The intestinal contents may be surrounded by a blood clot. In the chronic form the most characteristic lesions are found in the large intestines in the form of ulcers on the inner wall. The ulcers may be as large as a hickory nut and because of the rounded form are called ''button ulcers. ' ' The death of the tissue near the ulcer may be so extensive as to cause a perforation of the wall of the intestine, thus giving an opportunity for the intestinal contents to escape into the abdominal cavity. Such a Diseases of Hogs. 153 condition produces inflammation (peritonitis), causing death. In this type the spleen is not usually enlarged and the lungs are normal. Hogs are subject to intestinal troubles that are often mistaken for cholera, but may be differentiated from it through the fact that they do not spread to other herds. The trouble may be produced by unsuitable food, such as house refuse containing much soap. Often the mortality with such troubles is high, and the rapid death of the FIG. 18. HOG CHOLERA. Button ulcers on the inner wall of the intestine in a case of chronic hog cholera. (After Reynolds.) animals causes the farmer to think a contagious disease is present. The term ''swill-barrel" cholera is often used for such outbreaks. Prevention. As there is no cure for the disease, the owner must devote his efforts to prevention. The dis- ease may be brought onto a farm in a number of ways, most frequently, through the purchase of animals. As previously stated animals recover from the disease. Such animals may harbor the disease-producing bacteria in their bodies and disseminate them subsequent to ap- parent recovery As soon as such animals are brought 154 Agricultural Bacteriology. into a healthy herd, an outbreak develops, since many of the animals of the herd will be very susceptible to the disease. The bacteria are given off from the body of the affected hog in the manure and are taken into the body of the healthy animal with the food. No animal should be purchased from a herd in which hog cholera has been present during the previous year. Animals purchased should be kept in quarantine when first brought onto the farm, and then placed with a small part of the herd. If these exposed animals all remain healthy after two to three weeks, it is safe to place the- purchased animals with the herd. The method of keep- ing hogs in separate houses instead of in a large hog^ house has much to recommend it, for if cholera breaks out in one part of the herd, it can often be kept from spread- ing to the other sections of the herd. Hogs frequently acquire the disease from infected cars, shipping crates, etc. The disease may be spread from herd to herd by infected objects, such as farm tools carried from one farm to another. The farmer himself may inadvertantly serve to disseminate contagion, by visiting his neighbor to inspect an infected herd and bringing home the v virus of the disease in the slight amount of manure that may cling to his shoes. Birds and rats may also carry the disease. The exhibition of hogs at fairs is often a means of bringing the animals in contact with the disease. "When hog cholera is present in the neighborhood, the greatest care must be taken to prevent its introduction onto the farm. At the first signs of sickness in the herd, all animals that appear healthy should be removed to an- other field. All carcasses of hogs that have died of cholera should be burned or buried very deeply, first cov- Diseases of Hogs. 155- ering the body with quick-lime. Carcasses should never be thrown intd streams or left uncovered to decompose. The pens and yards should be thoroughly cleaned and well sprinkled with quick lime. The litter and manure should be burned. After a lapse of several months the pens should be whitewashed. The organism does not form spores, hence is easily killed. Vaccination and serum treatment. For many years efforts have been made to discover a vaccine that would protect from hog cholera as the black leg vaccine pro- tects against that disease, but the efforts have met with little success. Eecently methods have been devised that seem to promise success in preventing the spread of the disease. A hog that has recovered from an attack of hog cholera is immune to further attacks. If this immune animal is inoculated with the blood of animal that has the disease, the amount of protective substance in the blood of the immune animal will be greatly increased, so much so, that if some of its blood serum is transferred to a second animal, it will be protected against a natural attack of the disease for about a month. This method of prevention is similar to the use of antitoxin in lockjaw. If it is desired to make the protection more permanent, a small amount of blood from a diseased hog is injected into the animal at the same time the serum is adminis- tered. In this case the protection lasts for a long time, possibly during the life of the animal. Many difficulties are encountered in the use of the serum treatment in a practical way. It is to be hoped that these may be over- come and the method made a real success. The treat- ment can only be administered by a trained veterinarian, especially is this true when the virulent blood is used to- gether with the serum. 156 Agricultural Bacteriology. Swine plague. It is believed that swine plague is a distinct disease from hog cholera, produced by a different organism. The diseases often occur together, each pro- ducing its peculiar lesions in the body of the animal. From the standpoint of prevention, all that has been said concerning hog cholera applies to swine plague. It is not certain whether the method of vaccination against hog cholera is of any value in cases of swine plague. It is claimed by some that there is but one disease caused by an organism so small that it cannot be seen with the most powerful microscope, and that the organisms sup- posed to be the cause of hog cholera and swine plague are of secondary importance. Others claim that there are three distinct diseases. The disease of swine plague is primarily one of the lungs and it is supposed that the infection occurs through the lungs. The lungs may show consolidated areas, in which the organ has the appearance of solid flesh or liver, instead of the spongy normal texture, and the air pas- sages may be filled with an exudate. CHAPTER XVI. DISEASES OF FOWLS. There are a number of diseases of chickens and other fowls caused by bacteria. These diseases inflict a heavy tax on the poultry raiser and the general farmer. Pres- ent knowledge concerning these various diseases is far from complete ; in some cases not sufficient to control the disease with much hope for success. Chicken cholera. Chickens like swine are subject to dietary disorders which may often simulate a true con- tagious disease in the rapidity of its appearance and in the high mortality. It is certain that most of the out- breaks reported as chicken cholera are not caused by the specific organism of chicken cholera. Symptoms. The yellow color of the urates is the earliest symptom ; these in healthy birds are pure white. Diarrhea is present, the manure varies, sometimes being a pasty, greenish mass, a brownish-red slimy material or a thick clear liquid. The sick bird leaves the flock, be- comes weak and drowsy, acts dumpish, and the feathers are roughened. Intense thirst is usually noticed, the ap- petite is poor and the crop distended with food. The diseased fowls rapidly become poor. The disease makes rapid headway in the flock since the period of incubation is short, (one to three days.) Most of the affected birds die in a short time of an acute form of the disease;, others may have the chronic form, but recovery is rare. 158 Agricultural Bacteriology. Post-mortem examination. The liver is usually very much enlarged and softened; the intestinal organs are congested, but the changes are not such as make it easy to diagnose the disease. Manner of infection. The bacteria are found in the blood at the time of death. If any part of the carcass is consumed by well birds, they are certain to become in- fected. The only known manner of infection is by the food or water. The material that drops from the beak of the sick fowl may serve to contaminate the drinking water. The extensive lesions of the intestines allow blood to be mixed with the manure, and the contamina- tion of the food with this material is a cause of rapid spread of the trouble. The disease may begin in a flock by the introduction of a bird ill with the chronic type of the disease. Doves and wild birds are also supposed to be agents concerned in the spread of cholera. The improper disposal of dead birds, as by throwing them into a stream may cause in- fection of flocks at a distance. Prevention. Nothing can be done for the already in- fected bird. All efforts must be concentrated in pre- venting the spread of the trouble, by the prompt dis- posal of all dead birds, the killing of any that show signs of illness, thorough disinfection of the roosting houses, and the feeding and watering troughs. If pos- sible the flock should be moved onto fresh, uncontamin- ated grounds. The germ is easily killed by drying, sun- light, and disinfectants. It has been shown by experi- ment that it is safe to bring new stock onto land after a period of two weeks, if care has been taken in the disin- fection of the house and other contaminated objects. Diseases of Fowls. 159 Fowl typhoid. This disease is thought to be more widely spread than chicken cholera. The disease is less rapid in its progress in the individual bird, than is cholera. It is often mistaken for this disease for there are no marked differences in the symptoms. The diar- rhea so characteristic of cholera is usually absent and the intestines are pale instead of deep red, and the contents of normal consistency, while in cholera the intestinal con- tents are liquid and blood stained. It is not especially important that a correct diagnosis be made as to which of these diseases is present in the flock, since identical methods of prevention should be employed with either. Roup, or diphtheria in fowls. The disease of diph- theria of fowls is not caused by the same organism caus- ing diphtheria in human beings. It is considered to be the most important disease of chickens in this country. It is claimed that it affects turkeys, ducks, pigeons, and pheasants, as well as chickens. The cause of roup has not been discovered with certainty. The first symptom to be noted is a discharge of a wat- ery liquid from the nostrils, and often from the eyes, and the bird becomes dumpish. The breathing is often noisy, due to the obstruction of the air passages with the discharge ; the fowl may be able to breathe only by open- ing its mouth. Sneezing is frequent. Diarrhea appears later, the evacuations being greenish or yellowish. The eyes may be covered with the dried discharge, or they may be forced from their sockets, due to the accumula- tion of cheesy matter in the sockets. There are to be found in the mouth and throat, patches of grayish-yellow exudations, called false membranes which are similar to the membranes formed in the case of diphtheria in human beings. The closing of the throat by the membrane 160 Agricultural Bacteriology. causes death by suffocation. The accumulation of the exudate in the cavities of the head often causes a swelling, hence the common name for the disease "swell-head." The disease is to be differentiated from simple catarrh r which closely resembles the "cold in the head" of man. Simple catarrh is caused by improper ventilation of houses, dampness, cold winds, and exposure. Roup is often supposed to be produced by similar conditions. It has been shown experimentally that it is not possible to produce it by such means, although they undoubtedly favor its spread when once it is started in the flock. Prevention and treatment. The disease is most often introduced into the flock by the purchase of a bird having the disease in such a mild form that no symptoms are noticeable. Fowls that come from flocks in which the disease is present or has been recently present should not be placed with other flocks. Any bird showing an ex- udate from the nostrils or eyes should be removed from the flock at once. Care should be taken to avoid distri- bution of infection from diseased flocks to healthy ones, by means of the dirt on boots, farm implements, etc. The dipping of the heads of the affected birds in a 2 per cent solution of .potassium permanganate is said to be- an aid in the treatment of the disease. CHAPTER XVII. MISCELLANEOUS DISEASES. Diseases caused by wound infection. There are many diseases of domestic animals that are produced by organisms that enter the body through wounds. One of the most important is that known as white scours or diar- rhea in calves. It affects calves a few hours to a few days old, causing death in 70 to 90 per cent of cases. The discharges from the bowels are light colored, profuse and very offensive in odor. The animals lose flesh rapidly and have the appearance of suffering from severe sickness. The duration of the disease is from three to six days. It rarely attacks calves after they are from two to three days old. Once established in a stable, the disease may persist for years unless stringent means are taken to rid the stable of the infection. Treatment is of no value. Attention must be directed to prevention. It is believed that the organisms enter the body through the umbilical cord and that, if means are taken to prevent such infection, no trouble will re- sult. In order to accomplish this, the animal about to calve should be placed in a clean stall with an abundance of bedding. The tail, hips, and external genital parts should be sponged with a solution of carbolic acid or cor- rosive sublimate (1-2500). The cord of the young ani- mal should be cleaned carefully and a mixture of one ounce of tincture of iodine in two ounces of glycerine ap- plied. The treatment is to be repeated daily for three 162 Agricultural Bacteriology. or four days. The stable should be disinfected and all infectious matter destroyed. The infection of the umbilical cord in colts and lambs may serve to produce a general infection of the body with harmful organisms. Infection of the spermatic cord in the castration of colts often produces serious troubles. All minor surgical operations on animals should be carried out with regard to cleanliness of the part to be operated upon, the hands of the operator and his instruments. It is also generally believed that two very common troubles in the horse, fistulous withers and poll evil, are due to wound infection with pus-forming bacteria. The wound need not be a noticeable one, an irritation of the skin due to ill fitting harness, saddles or blows being suf- ficient to introduce the organisms found in the skin into the deeper tissues where growth is possible. Foot-rot in sheep is due, at least in many cases, to the infection of the tissues of the foot with pus-producing bacteria. The disease may pass from one animal to an- other until a large part of the flock is infected. The local application of disinfectants is the treatment em- ployed. Foot and mouth disease. Foot and mouth disease is one of the important diseases of Europe. It affects cattle, swine, and also man. From Europe it has been exported to other countries, especially to America. In 1870 it was present in New England and New York. In 1884 an outbreak occurred at Portland, Maine. In 1902 the disease was introduced into Massachusetts, New Hampshire, Vermont, Ehode Island; in 1908 in New York, Pennsylvania and Michigan. By prompt action, the disease was stamped out at each of these outbreaks. Miscellaneous Diseases. 163 The disease is marked by the appearance of blisters on the lips, gums, tongue, and inside of the cheeks. One or more feet may be diseased. Blisters appear on the coro- net and between the hoofs and often on the teats. Re- covery is usual except in very young animals. One important phase of the disease is that the organ- isms, whose nature is unknown, are often present in the milk. People using such milk in a raw form are thereby infected. The disease in man presents much the same symptoms as in the cow. Hogs also acquire the disease from milk. Distemper in horses. Influenza, or as it is frequently called distemper or pink eye, is a contagious disease, the cause of which is unknown. Infection takes place from horse to horse. The virus can be carried by infected human beings, litter and harness, etc. The period of in- cubation is two to seven days. The disease appears quickly. It is marked by a loss of appetite, a fever of 3 to 4 F. above normal, persisting for three to six days. The animal is dull; at first it is constipated; the feces are in hard balls, covered with slimy matter, later diar- rhea is present. The eyes are inflamed. The disease lasts six to ten days. From 2 to 4 per cent of the af- flicted animals die. Distemper in dogs. Distemper is the most important disease of dogs. The cause is not known; the period of incubation is four to six days. The eyes are inflamed, the exudate dries and often causes the lids to adhere to each other. Constipation at first, is followed by diar- rhea in which the feces have an offensive odor, and are often slimy and frothy. There is a nasal discharge. It 164 Agricultural Bacteriology. may affect the brain and the animal is then often thought to be rabid. The mortality ranges from 50 to 60 per cent. The only means of prevention of the spread of the disease is by isolation of all diseased animals, and the use of disinfectants. CHAPTER XVIII. DISINFECTION. It has been seen that the disease-producing bacteria pass from the bodies of living and dead animals in a number of ways, as in the material coughed up from the lungs, as in tuberculosis ; in the manure, as in hog cholera; in the milk, as in tuberculosis; in the contents of abscesses and carbuncles, as in anthrax, black leg, and pyogenic troubles, and in the discharges from the nostrils, as in glanders. The bacteria thrown off from the bodies of the diseased animal contaminate the stables, yards, and fields, and from these contaminated places and ob- jects often enter the bodies of healthy animals thus serv- ing to perpetuate the disease in the herd. If the farmer is to stop the spread of transmissible dis- ease, he must destroy in some effective way the bacteria that have been thrown off from the bodies of diseased animals. In short he must disinfect the barns and stables, and as far as is possible the yards and fields. In the destruction of the pathogenic bacteria consider- ation must first be given to the resistance of the organism it is desired to destroy. For this purpose the various disease-producing bacteria may be divided into two classes; those that ^produce spores and those that do not form these resistent bodies. The former class of bac- teria are very difficult to kill, the latter are easily de- stroyed. Fortunately, but two of the important dis- eases of animals are produced by spore-bearing bacteria. 166 Agricultural Bacteriology. black leg and anthrax. The most important and most common of the diseases affecting the domestic animals are caused by bacteria that do not form spores. Disinfectants. Disinfecting agents may be divided into two classes, physical and chemical. The effect of the most important physical disinfectant, sunlight, has been discussed in a previous chapter. Sunlight rapidly destroys all vegetating bacteria and their spores as well, if it falls directly upon them. If, however, they are cov- ered with a layer of dirt or dust even though it be very thin, the sunlight has little effect on them. Diffuse light, such as is present where the direct rays of the sun do not penetrate, is very weak in its action, requiring hours and days to produce the same effect as a few moments of di- rect sunlight. It is very certain that sunlight under the conditions that obtain in barns and stables has but little disinfecting action, because of the fact that the bacteria are protected from its action by the dirt and dust. Another physical agent of which little use can be made in the disinfection of stables is heat, either as dry heat or in the form of steam or hot water. Any small object of wood or iron can be easily disinfected by boiling. Thus, in the case of contagibus diseases of human beings, this process is frequently used. In the disinfection of stables etc., one is limited to the use of chemicals. Chemical disinfectants. The chemicals used for dis- infection may be divided into two classes, solid materials used in suspension or in solution, and gaseous. The lat- ter are by far the best when the conditions will permit of tneir use for the gas penetrates to every part of the space to be treated, even into cracks and crevices. This fact makes their use impossible except in a space that can be tightly closed, for the gas must be confined for several Disinfection. 167 hours in the space to be disinfected in order that the pro- cess shall be effective. The gaseous disinfectants find their greatest use in household disinfection, where the rooms can be tightly closed by pasting strips of paper over the door and window cracks. Formaldehyde, the best gaseous disinfectant, finds but limited use in the stable. Keliance must here be placed on the disinfect- ants that can be applied in solution or suspension in water. There are a considerable number of these but three or four are by far the most important. Lime. Quick lime or stone lime is made by heating lime stone to a very high temperature. The lime stone is changed because of the loss of carbon dioxide, which passes off as a gas during the burning of the lime stone. The quick lime thus produced gradually changes on ex- posure, to a powder known as air-slaked lime which has the same composition as the original lime stone, and which has no disinfecting action whatever. If the quick lime is: treated with six parts of water to ten parts of lime, water-slaked lime will be obtained, which, when prepared in a cornet manner, is a dry white powder, resembling air-slaked lime in appearance but not in composition. This can be noted by placing a particle of each on the tongue for a moment. The air-slaked lime tastes like so- much chalk while the water-slaked soon causes the tongue to burn. It is caustic lime and has disinfecting proper- ties. It can be used as a dry powder, sprinkled on floors and yards, or in a suspension, in water as whitewash. The whitewash is best applied with a spray pump and for this purpose must be made rather thin so as not to clog the nozzle of the pump. Any of the hand spraying out- fits are well adapted for the application of whitewash or other disinfectants to the walls and ceilings of stables. 168 Agricultural Bacteriology. Lime is cheap, and can be procured everywhere. If the whitewash is prepared from good lime, its disinfect- ing properties are probably as great as those of any other substance that can be used to advantage in stable disin- fection. It has, however, little effect on spores of bac- teria. The whitewashed walls and ceilings make the stable much lighter than would otherwise be the case. The dry water-slaked lime is especially valuable for the treatment of yards and pens infected with hog cholera bacilli and for covering the carcasses of all animals that have died of any of the transmissible diseases, and which are to be buried. Carbolic acid and cresol compounds. Carbolic acid appears on the market in the crude and purified forms. The former is a black, oily liquid that will not mix with water, unless treated with strong acids, such as sulphuric acid, or with strong alkalies. The pure carbolic acid is in the form of white crystals, which on the addition of 5 per cent of water, and on warming, changes to a clear liquid of the consistency of syrup. For use as a general disinfectant, this liquid is added to water so ato make a 5 per cent solution. A stronger solution than this will not dissolve in water/ Both the crude and purified carbolic acid are being re- placed for disinfection purposes by the different proprie- tary compounds such as ZenoLeum, Kresol, etc. These substances have, as a rule, greater disinfecting powers than carbolic acid, a 2 per cent solution being as effective as a 5 per cent solution of carbolic acid. They mix with water in all proportions, forming a milky white emulsion that can be easily applied with a brush or spray pump. They are less caustic and poisonous than carbolic acid, but their cost is somewhat more. D/sinfcction. 169 Corrosive sublimate. This compound, frequently called bichloride of mercury, is the strongest disinfectant known. Its great disadvantage as a stable disinfectant is its poisonous properties, which preclude its use on mangers. It is used in a one to one thousand solution, one ounce in eight gallons of water. It kills all forms of bac- teria in a moment and the spores in a short time when no substance is present that will combine with it and thus destroy its action on the bacteria. In the presence of dirt and manure its effect is greatly reduced. Ferrous sulphate and copper sulphate. These sub- stances known as green and blue vitriol, respectively, were formerly considered to be good disinfectants. It is now known that they are almost worthless in this re- spect. They are rather to be classed as deodorants, and can often be used for this purpose to good advantage. A substance that will counteract the odors produced by bacteria does not necessarily destroy the bacteria them- selves. Formaldehyde. This disinfectant is sold as a solu- tion of the gas, formalin, in water. It can be applied as a 5 per cent solution, but since the gas at once passes off, it has but little value as a stable disinfectant. Small objects, other than those of leather, to be disinfected can be placed in a solution of formaldehyde. The process of stable disinfection. Whenever a sta- ble is to be disinfected, the first process should be to give it a thorough cleaning. It should be remembered that no disinfectant can kill a disease-producing organism with which it does not actually come in contact. If the organism is protected by dust, dirt, and dried manure, its destruction is difficult. The most of the disease-pro- 170 Agricultural Bacteriology. ducing germs will be in the dirt and manure of the stable. If the stable is thorough^ cleaned most of the bacteria will have been removed. All loose woodwork, especially box mangers, should be removed. The walls, ceilings, and floors should be mois- tened by spraying with a solution of corrosive sublimate so as to prevent dust in the subsequent operations. The loose material should all be removed ; the walls and floors scraped until all dried manure and dirt is removed and the bare wood or concrete exposed. All the material re- moved should be burned, not thrown into the yard with the cattle. The stable should now receive a good coat of whitewash applied with a spray pump so .that it will penetrate all cracks. Both walls and ceilings should be treated, and the floors sprinkled with the dry water-slaked lime. The mangers should be, scrubbed with a hot solu- tion of lye, or a 5 per cent solution of carbolic acid. The actual process of disinfection should be supplemented by making provision for abundant , light and air. A half- hearted job of disinfection is worse than none at all, since it gives a fancied security, but little real security against a re-occurrence of the disease. The disinfection of x yards is difficult. It can only be attempted. The sprinkling of a liberal amount of dry water-slaked lime is the best that can be done. The dis- infection of fields is impossible. Small areas may be limed or burned over. Neither of these methods is likely to be effective in the case of spore-forming bactria. All other forms will soon die without the addition of any disinfectant. SECTION IV. RELATION OF BACTERIA TO SOIL. CHAPTER XIX. RELATION OF BACTERIA TO FERTILITY. The farmer is interested in the soil as the home of the plant. Unless its home is one favorable in every way to the kind of plants the farmer is attempting to grow but meager yields will reward his efforts. In order that the soil shall be a favorable place for such growth, a num- ber of conditions must be present. Its physical proper- ties are important. It must not be hard and dense so that the delicate roots of the young plant in search of food cannot make their way through it. It must be in good tilth. Moisture, not too abundant or too small in amount, must be available. The temperature of the soil must be conducive to rapid plant growth. These things are all important and are to a great extent at least under the control of the farmer. Plant food. Another important condition required is the presence of a sufficient supply of plant food in an available form f or 4ise by the plant. Certain chemical elements as potassium, calcium, magnesium, phosphorus, nitrogen, sulphur, and iron are essential in order that normal development may occur. These substances the plant obtains from the soil. The carbon, oxygen, and 172 Agricultural Bacteriology. hydrogen which are as essential as the other chemical elements mentioned are always abundantly present in an available form in the water and in the air. The elements obtainable from the soil are a greater source of worry. to the farmer. While the soil, as a rule, contains large amounts of these different elements, they may be present in such forms that they cannot be utilized by the green plant. "While they represent plant food, it is of no immediate value because unavailable. This material is, however, undergoing a change in form that renders it more and more available. A large number of agencies are at work, causing this change and amongst them biological factors are very important. As indicating the relatively large amount of unavail- able plant food that may be present, the following analy- sis of 49 American soils are presented. The total nitro- gen, phosphorus and potash content of the first eight inches was as follows : 2600 pounds of nitrogen per acre, 2090 pounds of phosphorus, and 7400 pounds of potas- sium. The other essential elements are usually present in larger amounts and therefore are not so likety to be depleted in the soil as are the three mentioned. The amount of any of these elements that are available at any one time is usually very small indeed. Often, it is not enough to furnish what is needed for a single crop. The potential but immediately unavailable supply must be constantly changed into available food at a rate suffi : ciently rapid to supply the plant so that growth may go on rapidly or otherwise the crop will be a poor one. A fertile soil may, in one sense, be defined as one in which unavailable plant food is being changed to available food at such a rate that there is an abundant supply at all Relation of Bacteria to Fertility. 173 times to allow of a rapid and luxuriant growth of the plants. The food to be available to the plant must be in solu- tion so that it can pass into the roots of the plant. Such soluble material is easily lost in the drainage water that leaches from the soil during the wet times of the year. Thus, if more of any one element is made available than the crop can use, it is very likely to be lost during the winter and spring, and the soil thus robbed of its fer- tility. An ideal condition is to have enough of each ele- ment rendered available so as to ensure an abundant crop, but not to have an excess. This ideal condition cannot be realized but much can be done by the farmer to conserve the fertility of his soil by methods which will be mentioned later. If any one of the essential elements is lacking, or is present only in small amounts in available form, it will act as a limiting factor to the yield. One element is as essential as another. Any may be the limiting one. If this be added to the soil in the form of a fertilizer, an immediate increase in yield is noted. For this reason the use of commercial fertilizers is so extensive. The fer- tility can also be restored by treating the soil in such a way as to render the unavailable plant food available. For example, it ; has been shown in certain of the wheat fields of the Rothamsted Experiment Station in England that the amount of available phosphorous present in the soil was so small as to limit the yield, yet this same soil contained a large amount of the element in an insoluble form. By treating the soil in a proper manner so as to allow the growth of certain kinds of bacteria, the phos- phorus would be made soluble and the fertility of the soil improved. 174 Agricultural Bacteriology. The same is true with reference to the other essential -elements. It thus becomes important to know something concerning the. conditions that are favorable for the growth of the bacteria in the soil. The yield of the vis- ible crop is dependent on the way in which the farmer favors the growth of the invisible crop. This presents a new phase of soil management which has not long been recognized, as the soil has generally been regarded as an inert mass of particles of sand, clay, or gravel, inter- mixed with more or less dead organic matter which gave to the upper portion its black color. Since there is no store of available plant food in the soil and since the bacteria are necessary in order to change the raw food to a fitting form, it is evident that a soil that is free from bacteria cannot be a fertile one. If various types of soils are examined as to the number of bacteria, it will be found that those of high fertility are teeming with bacteria while a poor sandy soil will contain very few. Distribution of bacteria in the soil. The soil is one of the great homes of the bacteria. In a state of nature, i. e., in uncultivated soil, everything that the soil yields is returned to it, either directly in the i form of the dead plant, or indirectly in the body or excreta of an animal that has lived on the plants. This means that organic matter in abundance is supplied as food to the bacteria; hence their rapid increase in numbers where requisite conditions obtain. This activity renders still more raw plant food available with the result that the soil con- tinues to increase in fertility until there have been formed from the bare rock by the aid of various physi- cal agencies that help in disintegrating the rock such fertile soils as are found on our western prairies. Relation of Bacteria to Fertility. 175 It is impossible to determine in any way the total number of bacteria in the soil. What can be done is to determine the number that will grow on such substances as are used in the laboratory as culture media. Exam- ined in this way a sandy soil will be found to contain a few hundred thousands in each gram (1-30 of an ounce) while a rich loamy soil may contain several million per gram. A garden soil may show ten, twenty-five, or even fifty millions of these minute plants so essential to the fertility of the soil. The greatest number of bacteria is found in the first few inches of the soil, in what is known as the soil proper. In the sub-soil smaller numbers are found and as still lower depths are examined the bac- teria decrease rapidly in numbers. At a depth of a few feet they completely disappear. The reason for this rapid decrease in numbers is due to the lack of food and air, and to the filtering effect of the soil. In the upper layers of the soil food is abundant and other growth con- ditions favorable. The soil contains a large number of different kinds of bacteria of the most varied nature and appearance. It is the home of some of those that produce diseases in man and animals, as well as the most of those forms that cause the spoiling of food substances, and the various fermen- tations, many of which are so important. The number of bacteria in the soil is influenced by a number of fac- tors, chief of which is the amount of food present. The addition of organic matter in the form of stable manure, or plowing under a green crop, increases the amount of food material, thus stimulating the growth of bacteria. The effect of temperature is also of importance. As the soil becomes warm in the spring, the conditions be- come more favorable and the bacteria increase rapidly in 376 . Agricultural Bactenoiogy. numbers. The rise in temperature has more effect at this time of the year than later, since the supply of avail- able food is likely to be greater than during the summer an.'l fall, due to the fact that the remains of the previous crop are added to the soil. The moisture content also exerts an influence. Bac- teria demand a considerable amount of water for their growth. If the soil is very dry, cell development is slow or ceases. Again, if the soil is water logged as in marshes and low lands, the growth of certain essential kinds of bacteria is impossible, due to the fact that they cannot get a supply of oxygen. Such wet soils warm up very slowty and this acts as a restraining factor in bac- terial growth. If the low places are drained, the ex- cess of water is removed and air is allowed to penetrate the soil and bacterial action is more rapid, both because of increased aeration and higher temperature. The effect of an abundant supply of oxygen is to increase the growth of the most important classes of soil bacteria as is noted in soils thoroughly cultivated. Permanent pas- ture and woodland soils are poorly aerated and in them certain kinds of bacteria grow poorly. As a result these lands never produce such large amounts of plant growth each year as does the same soil under cultivation. The bacteria as a rule grow best in an alkaline medium, and this is especially true of many soil bacteria. The soils of marshes and lowlands in general is apt to be acid in reaction. Soils that have been cultivated for long* periods without having had returned to them organic matter, barnyard or green manures, tend to become acid. In such soils the bacteria cannot grow well. If the acid- ity is neutralized by the addition of lime, the number of bacteria will increase. In an acid soil, the addition of Relation of Bacteria to Fertility. 177 4000 pounds of limestone per acre increased the number of bacteria from 440,000 per gram to 6,600,000 in a period of seven weeks. It will be seen that whatever makes the soil a better home for our cultivated plants, increases the number of bacteria in it. The question at once comes to mind: Is the increased fertility as shown by the larger crop, the cause of the growth of the microscopic plants, or is. the rapid growth of the bacteria the cause of greater fertility, and hence the larger crop of corn or oats, etc. results ? As will be seen, the latter is the true statement. Without great bacterial activity in the soil, large crops cannot be grown. Higher forms of life in the soil. Bacteria are not the only forms of life that live in the soil and exert an effect on its properties. In acid soils, molds may grow luxuriantly. The soil also contains various kinds of tiny green plants found so abundantly in water, the green algae. Still larger forms of life are of great importance, such as the common angle worm, that, by its formation of burrows, brings the lower layers of the soil to the sur- face, and thus in the course of a few years, turns the soil over as completely as does the farmer's plow. The burrows allow the air to penetrate into the soil. The land under permanent grass is thus aerated and culti- vated by these animal forms. These and all other low animal forms live on organic matter ; they help to decom- pose it, and are in turn decomposed by bacteria. Sta- tistics that have been collected indicate that each acre of land supports as much life, measured in pounds, in the shape of low animal forms, as the farmer keeps in the form of domestic animals. The soil is. thus, not a dead and inert mass, but some- 178 Agricultural Bacteriology. thing teeming with forms of life of the greatest import- ance to the farmer. It is a manufacturing establish- ment where plant food is made from raw materials. To furnish the workers favorable conditions is one of the problems the successful tiller of the soil must solve. Decomposition of organic matter. The material re- turned to the soil under natural conditions or by the farmer in the form of stable manure or the crops plowed under (green manuring) is organic in character, i. e., the result of plant and animal growth. It contains the elements that are necessary for succeeding crops of vege- tation, but in such a form that they cannot be used until they have again been brought to the same condition as when they were first taken up by the plant. The organic matter added to the soil embraces every conceivable type of matter, yet, everything serves as a food for some form of life, and is thus decomposed to some extent. Other kinds of life then use the by-prod- ucts of the first and so on until the ultimate stage is reached and the elements can be again made use of by a new crop of wheat, corn, or other plant. The spoiling of our food stuffs, rotting of apples, and potatoes, the sour- ing of milk, the putrefaction of meat, and the rotting of manure, are but steps in this great series of decomposi- tion processes carried on largely by bacteria. The digestive changes occurring in all kinds of ani- mals are but initial steps in the decomposition of organic matter, since the material given off from their bodies is much more simple than the food absorbed and is much more easily brought, by the action of bacteria, into a form that can be used by the green plant. The various kinds of matter added to the soil can be divided into three classes: 1st. The carbohydrates; 2nd. Relation of Bacteria to Fertility. 179 the protein substances, and 3rd. the fats. The first are composed of carbon, hydrogen, and oxygen and include such substances as starch, sugars, cellulose, and woody fiber; the third is made up of the same elements, and is represented by the animal and vegetable fats and oils. When these substances are completely decomposed, the elements appear as water, and carbon dioxid (C0 2 ), both of which can be used by the plant. Protein material contains in addition to the above ele- ments nitrogen, sulphur, and phosphorus. The end products of their decomposition are carbon dioxid, water, ammonia, free nitrogen, hydrogen sulfide, and some com- pound of phosphorous. The ammonia, hydrogen sul- fide, and phosphorous compounds must be further changed by certain kinds of bacteria before the green plant can use the nitrogen, the sulphur or the phos- phorus. The simple end products, carbon dioxid and water, of the bacterial decomposition of organic matter do not in- terest us further. The compounds that are formed dur- ing the stages of decomposition are of more importance because of their influence on the soil. The decomposition is carried on by both aerobic and anaerobic forms of bacteria. The great distinction be- tween their work is that the work of the first is complete ; the most simple products resulting, such as carbon dioxid, water, and ammonia. The material acted upon dis- appears as completely as though it had been burned. With the anaerobic bacteria the work is not wholly fin- ished, but a part of the material remains in the soil, and forms what is known as humus. Because of the fact that in cultivated soil, conditions are favorable for the aerobic bacteria, humus does not 180 Agricultural Bacteriology. accumulate. On the other hand in land under grass, in woodland and in wet lands the anaerobic bacteria grow best. Here the decomposition of the vegetable residue is not complete and the humus accumulates in the soil. When the lowland is drained, or the prairie broken, the aerobic bacteria begin to act on the humus, and grad- ually destroy it. The land now produces more than in its wild state, but unless organic matter is returned to it as manure, etc., it gradually diminishes in fertility, as has been so well shown in the eastern part of the United States. The burning of the straw on the prairies of Miij- nesota and Dakota is one way in which the fertility of the land is destroyed. The straw, if it had been plowed under, would have helped to keep up the humus content of the soil. It would have furnished the bacteria food, and the result would have been a much less rapid de- crease in fertility in those fields, the soil of which the settlers thought could never be exhausted. In a sandy soil, the aerobic bacteria grow rapidly and any organic matter added is soon completely destroyed; while in a close soil like a clay, the decomposition pro- cesses go on much more slowly. The effect of a heavy coating of manure is .often to be noted only during the season in which it is applied to a sandy soil, while on a clay soil it may manifest its effect in the second and even in the third year. In some kinds of farming, the farmer cares little for the fertility of the soil, but wishes one that will allow the rapid growth of bacteria which are to decompose the manure that is added. The market gardener, with an abundant supply of manure from the city, wishes such a soil, simply a place for the bacteria to work on the raw material he adds to the soil. Relation of Bacteria to Fertility. 181 The green -plant gets its supply of carbon from the carbon dioxide of the air. Only a small amount is pres- ent in the air at any one time, so little in fact that if the supply were not renewed it would soon be exhausted. This renewal comes from the decomposition of Organic matter by bacteria. The respiration of plants and ani- mals also produces carbon dioxide. The burning of fuel also frees the carbon as carbon dioxide. There is thus a constant passing of the carbon from the air to the plant and back again to the air through the action of plants, animals and especially the bacteria of soil. CHAPTER XX. EFFECT OF BACTERIA ON MINERALS OF THE SOIL. The water that falls on the soil in the form of rain contains no mineral matter in solution. If the water from a well or that which runs from a drain is exam- ined, it will be found to contain a varying amount of ma- terial that has been dissolved from the soil through which the water has passed. Most of the mass of the soil is insoluble in pure water, hence there should be found but a very small amount of mineral matter in the drainage water unless there are factors at work in the soil, changing the insoluble minerals into soluble com- pounds. It has been seen that the bacteria render the various kinds of organic matter soluble, and that the prod- ucts formed by. their action are water, ammonia, and car- bon dioxide together with some less important products. Many intermediate pro consequently much greater. Nitrogen fixation by bacteria without the aid of plants. With those forms of bacteria that form the nodules on leguminous plants, no fixation of nitrogen is supposed to take place, except in the nodules of the plant. The bacteria are known to exist in the soil for a number of years even though no leguminous plants are grown on the field. It is thus evident that the bacteria must be able to grow in the soil outside of the plant. There are found widely distributed in the soil, other Fixation of Nitrogen. 205 kinds of bacteria that are able to fix the free nitrogen of the air and build it up into their own protoplasm. They are able to grow in media that contain no nitrogen and must then satisfy their needs from the nitrogen supply of the air. It is supposed that a large part of the nitro- gen of the soil has been brought into combination by the action of these bacteria. It has been shown that a soil on which no plants of any kind are growing will increase in its content of nitrogen, and it is believed that it is. largely due to these germs. Unlike the nodule-forming bacteria, the fixation of nitrogen by this second class, known as the azotobacter group, can go on independent of the kind of plants that may happen to be growing in the field. It is important to know the conditions that favor the growth of these nitrogen-fixing bacteria. They are aerobic ; . hence, grow best in a soil that is thoroughly aerated, stirred and drained. They demand a supply of available potash and phosphorus as well as organic mat- ter from which they derive the energy necessary for the fixation of the nitrogen. In the laboratory the largest amount of nitrogen is fixed in a food medium that con- tains a sugar such as cane sugar or mannit. In the soil, it is believed that they use the different carbohydrates contained in the plant residues that are added in the roots of crops, in the green crop plowed under, or in the manure. In the case of uncultivated land, the greater part jf the annual crop falls onto the ground, and undergoes de- composition. The nitrogen-fixing bacteria are thus fur- nished with suitable food to accomplish the fixation of nitrogen, and the content of the soil in this important 206 Agricultural Bacteriology. element slowly increases. On cultivated fields this crop of organic matter is largely removed, so that conditions are not so favorable for the development of this type of life. As a consequence less nitrogen is brought into com- bination, and a more rapid depletion of the total nitro- gen supply of the soil takes place. CHAPTER XXIII. BACTERIA IN MANURES. The waste products of the animal body are elimi- nated largely in the urine and feces. The latter consist, in the main, of the undigested and indigestible parts of the food; the urine contains the waste of all activities of the different tissues of the body. The changes that the food undergoes in the body of the animal, must be looked upon as a part of the complex process by which organic matter is again rendered available to the green plant. The material that is eliminated from the animal is much more easily decomposed by bacterical action than is the food consumed. That which comes from the in- testinal tract is already well advanced in the series of changes that occur in the transformation of the organic matter into stable form. It is interesting to know that the work of the bacteria begins in the body of the animal, and that their action on certain parts of the food is of value to the animal, enabling it to make use of parts of the food that without their aid would be impossible. As previously noted, the alimentary tract of animals is to be considered as one of the natural homes of the bacteria. Food is abundant, while temperature and moisture conditions are favorable for rapid growth. Over one-fourth of the solid matter in human feces con- sists of bacterial cells. In the feces of the domestic ani- mal, the proportion of bacteria is much less because of the nature of the food. ^Millions of bacteria exist in every gram of the manure. 208 Agricultural Bacteriology. Digestion of cellulose. Coarse fodder, such as hay r straw, or corn fodder contains a large proportion of crude fiber or cellulose. It is known that different kinds of animals can digest this class of substances to a varying extent. In the different digestive juices of the body have been found enzymes that can attack carbohydrates, fats and proteins. None have been discovered that have any action on cellulose. There are in the feces of animals, bacteria that can digest the cellulose, changing it to com- pounds that can be used by the animal. It is asserted that ruminating animals can digest 75 per cent of the cellulose in their food, and the horse 50 per cent. Dogs and the strictly carnivorous animals cannot utilize this material at all. In the case of the ruminating animals the food remains in the body for a long time, as for in- stance, in the cow for six or seven days, and with sheep possibly a still longer time. There is thus opportunity for extended bacterial action in such a favorable environ- ment. In man the food passes through the body in a much shorter time, and there is not the opportunity for the bacteria to attack the cellulose. It is very probable that the bacteria of the intestinal tract are necessary to the well-being of all kinds of ani- mals. At the time of birth, the intestines are free from bacteria but within a short time, less than a day, the bac- teria have invaded the entire tract. Definite kinds 'of bacteria are found to occur. When these are replaced by other forms, the animal is quite likely to suffer. Composition of barnyard manure. Manure is made up of the solid and liquid excreta of the different kinds of animals kept on the farm and of the litter used in the stables. It thus contains all of the compounds found in the plant, and will undergo, in the main', the same set of Bacteria in Manures. 209 changes that the plant tissue does in the soil. As has been previously stated, it is of the greatest advantage to the farmer to return to the soil as large a part of the ma- terial removed in the crop as possible. This is true not only for the mineral ingredients of the soil, as potassium and phosphorus, but also for the organic matter. The problem of the farmer is to handle all manures made on the farm in such a way that the least loss may occur. Decomposition of manure. Manure when placed in piles rapidly decomposes under the action of micro-or- ganisms, continuing as it were, the changes inaugurated in the intestinal tract. The bacteria voided with the ex^ creta serve to inoculate the bedding or litter used. The bacteria decompose the organic matter with the result that in a well-rotted manure, but little trace of the ma- terial used as bedding can be found. Nitrogenous compounds. Stable manure contains various nitrogen-containing compounds that are found in the plant. These undergo a process of ammonification, due to the action of the same kinds of bacteria that are responsible for similar changes in the soil. A part of the nitrogen that is used in the cell processes of the animal is eliminated in the urine in the form of urea, uric acid, and hippuric acid. These substances are converted into ammonia salts. In the summer the odor of ammonia is often noticeable in horse manure, due to the decomposi- tion of the nitrogenous compounds in the urine. The am- monification of the nitrogen in the solid manure and in the litter is less rapid. As ammonia is readily soluble and is also volatile, it follows that where fermentation is rapid much of this valuable fertilizing ingredient is lost in the leachings from the pile or passes off into the air. 210 Agricultural Bacteriology. Much of this loss can be prevented by the use of proper methods which will be described later. In the manure heap the ammonia is not changed into nitrates as it is in the soil for the conditions are not fav- orable for the nitrifying bacteria. Organic matter is too abundant and oxygen is also lacking except in the outer layers of the pile. If the manure is allowed to stand, especially if it has been mixed with earth, until it is com- pletely decomposed, a small amount of nitrate will be found. Since no nitrates are formed, denitrification can- not take place. Cellulose decomposition. The decomposition of the cellulose begun in the animal is continued in the manure pile by the same kind of bacteria as in the body of the animal. The starches and sugars, etc., are also readily fermented by micro-organisms, and carbon dioxide, water, hydrogen, and organic acids are formed. Losses from manure. It is impossible to return to the soil all of the organic matter removed in the crop, even though the entire crop is fed to farm animals and the manure carefully handled. In the respiration of ani- mals a large amount of carbon is eliminated from the body ; this was taken^ in with the food. Oxygen and hy- drogen in the form of water are given off as respiratory products and in the perspiration. The nitrogen and mineral ingredients are eliminated in the same amounts as are contained in the food consumed, except for the quantity retained in the tissues of the animal. This is of course much more, in the case of a growing than a ma- ture animal. In the decomposition processes in the manure pile, the organic matter is destroyed, which is in itself a loss to the soil, since if applied to the land, it would have fur- Bacteria in Manures. 211 nished food for bacteria, especially the nitrogen-fixing ones, and have added to the humus content of the soil. J t is now realized that the value of manure is not deter- mined alone by the amount of potassium, phosphorus, and nitrogen it contains, but the organic matter itself exerts a most important effect. Market gardeners find it advantageous to pay more for manure than the fertiliz- ing ingredients alone would cost in the form of commer- cial fertilizers. For most soils the greater the amount of organic matter that can be returned the better for the soil. The practice of hauling manure directly to the field from the stable is probably the most successful means of conserving its value. If very large amounts of manure are to be applied, as in market gardening, unrotted manure cannot be used on account of its injurious effect on the crop. The amounts usually applied in farm practice have no injurious effect. The potassium and phosphorus of the manure are changed to soluble form in the decomposition processes. These can be lost from the manure only through the leaching of the pile. The largest loss is liable to occur in the case of nitrogen when ammonia is freely formed. In order to prevent the loss in the latter form, materials such as gypsum, kainit, sulphuric acid, and peat, that were supposed to fix the ammonia, were formerly em- ployed. It is now recognized that the loss prevented by their use is very small, and they are no longer used to any extent. Hot and cold manures. Horse and sheep manures are called hot manures because if placed in a pile they heat or fire fang. Cow and hog manure are cold ma- nrires. During their decomposition enough heat is evolved to keep them from freezing in quite severe 212 Agricultural Bacteriology. weather, but they never fire fang. This difference is primarily due to the physical condition of the manure and to its water content. The horse manure is dry and open, allowing the air to penetrate into the pile, while cow manure, even when large amounts of bedding are used, is of such a physical texture that air cannot enter. The large amount of air in the horse manure permits the growth of aerobic bacteria and molds. The heat evolved by their respiration is great and the decomposition they produce very complete. The organic matter is practi- cally burned, the carbon, hydrogen, and nitrogen pass- ing into the air. Where decomposition occurs under an- aerobic conditions the process is much slower and less complete. If a pile of horse manure is well packed, so as to exclude the air, the usual aerobic fermentation will not occur, but will be supplanted by anaerobic action. In such a case the loss of nitrogen and organic matter will be much less. In handling any manure, the activity of aerobic organ- isms should be excluded as far as possible by piling the manure in large compact piles of considerable depth. If the man are is allowed to accumulate in the stalls or feed- ing sheds in which the animals run loose, the loss will be reduced to the minimum, since the constant tramping of the animals excludes the air, and the manure is protected from leaching. If the manure is hauled directly to the field from the stall the decomposition goes on to some extent on the sur- face, but the soluble products formed pass into the soil. There may be some loss of nitrogen as ammonia, but it is certain that the losses are much smaller than when the manure is allowed to rot in piles. If it is not possible to apply it directly, the piles should be thoroughly packed Bacteria in Manures. 213 and, if under cover, should be kept moist. The average difference in temperature between a loose pile of cow manure from which the water was allowed to drain, and one placed in a tight concrete pit and well packed, was 98 F. for one month after the manures were placed in the pits. Heat in the manure pile indicates a combus- tion of organic matter as much as in a furnace. The loss from the loose pile amounted to 53 per cent of the or- ganic matter and 34 per cent of the nitrogen ; in the com- pacted pile the losses were 28 and 15 per cent respec- tively. CHAPTER XXIV. WATER SUPPLY AND SEWAGE DISPOSAL. An abundant supply of pure and healthful water is one of the necessities of modern life, whether in the city or on the farm. In the city, the home is provided with this ne- cessity through the action of the municipality ; the indi- vidual citizen does not have to concern himself with the question as to the source and quality of the water sup- plied, while on the farm the problem of obtaining a plen- tiful supply of water fitted for household purposes is an individual one, and one that is frequently neglected, al- though it means so much to the comfort and health of the farm home. Modern cities are spending immense sums of money in securing safe and adequate water supplies and in pro^ tecting them from pollution. The farmer should use the same foresight and the cost for supplying the farm home with good water will be no greater than must be paid by the home in the city. Relation of water to disease. A number of transmis- sible diseases may be carried from one person to another through the medium of the drinking water. The most important of these are typhoid fever and cholera. The former, a world-wide disease, the latter one that is not found at present in America and Western Europe. The reason these diseases are often spread by means of water is to be found in the fact that the bacteria are given off from the body in the urine and feces and as great care- Water Supply and Sewage Disposal. 215 lessness often prevails in the matter of disposal of house- hold sewage, the water supply becomes contaminated. The sewage of a city may be discharged into a river, from which another city a few miles further down draws its water for household use. A city may discharge its sew- age into a lake and from the same source draw its water supply, as is the case with nearly all the cities on the Great Lakes. Under such conditions more or less of the sewage is certain to enter the water mains. As stated in the discussion on the relation of milk to transmissible dis- eases, there are people who have recovered from typhoid fever and who continue to harbor in and give off from their bodies the disease-producing organisms. These people are supposed to be the means by which the disease maintains its presence in the community, no matter how much care may be used in the disinfection of the dis- charges of persons known to be suffering from typhoid fever. Cities now realize that it is economy for them to- protect themselves by securing their water supply from sources known to be free from pollution with sewage, or through purification by the proper filtration of water from suspected sources. The farm home should likewise be insured against ty- phoid fever through the protection of its water supply from sewage pollution. It is frequently thought that typhoid fever is an urban disease, but as a matter of fact it is more prevalent in the country. The city home is ex- posed to infection by means of the water from many other homes in which typhoid may be present, while the farm home is not related in so direct a manner with other places in which the disease may be present. There, are, however, abundant ways in which the disease may be brought on to the farm. 216 Agricultural Bacteriology. Relation of water to soil. As was previously stated the upper layers of the soil are rich in germ life. The drainage water from such places will be teeming with bacteria. The shallow dug well, loosely bricked up, is filled during the wet seasons with water coming from the upper layers of the soil. If material containing disease- producing bacteria is placed on the ground near the well, as in a privy vault, the bacteria may be carried by the percolating water into the well. The distance between the vault and the well that is required to prevent pollu- CESS POOL FIG. 21. POLLUTION OF A WELL. The well water may be polluted from a cess pool or vault by the percolation of the ground water into the well. (After Harrington.) tion of the well can not be stated in definite terms as it will depend on the nature of the soil, whether it is close and dense as in a clay soil, whether it is porous, as a sandy soil, or whether the percolating water may form channels in it, as in lime stone. The distance that may be tra- versed by bacteria in the underground water also de- pends on the slope of the underlying rocks. A well on Tiigher ground than a privy is not necessarily protected from pollution. Water Supply and Sewage Disposal. 217 As the water percolates through the soil, the bacteria are removed until at a varying depth beneath the surface no organisms are found. The water that enters a well from the lower layers of the soil may be free from bac- teria. Such a supply is the most desirable if it can be pumped from the well in the same condition as when it entered. In order to obtain the water in this condition, the well must be protected from all surface drainage. It is very difficult to obtain this condition except in the case of a drilled well which is cased with a threaded iron pipe, and which is protected at the top so that no water can enter the casing. A dug well, even if provided with a tight wall to a considerable depth, is likely to receive more or less surface water and hence is liable to pollu- tion. The well should be so arranged at the surface that no surface water, or water that is pumped onto the curb can enter the well, for material containing disease-producing bacteria may be brought on to the curb and in this way pollute the water. The dug well, so common in the older sections of the country, is a menace and should be re- placed by the safer drilled well. The old-fashioned well with bucket and sweep, which is so often regarded with sentiment, is the most dangerous type of well, even though the water is clear and sparkling. The water of a well that receives surface drainage is not harmful at all times, but it may become so at any time. The conditions needed to produce disease are all present except one, viz, the deposition of material that contains disease-producing bacteria within the zone from which the water percolates into the well. This essential condition may not be present for years, but at last it is 218 Agricultural Bacteriology. introduced and an outbreak of typhoid fever occurs in the family. On the diary farm, as previously mentioned, an oppor- tunity is offered for the farther spread of the disease by means of the milk infected from the water or in some other way. The wise course to follow is to supply thd home with water that is so protected that it cannot be the cause of disease, even if material containing typhoid bac- teria is deposited near the well. This demands a well into which no water can enter except that which has per- colated through a sufficient bed of soil to insure its free- dom from all harmful bacteria. This demands again the positive exclusion of water from the upper layers of the soil by the use of a non-porous wall, preferably an iron * pipe, and the protection of the well at the surface. Springs are the outlet of under-ground streams. Spring water is free from bacteria as it flows from the ground and is, of course, an excellent water for house- hold use, but there is often danger of surface pollution entering the basin of the spring, unless it is carefully protected. The first consideration in obtaining water for the home should be to secure a safe supply that is thoroughly pro- tected from all possible pollution with disease-producing bacteria. An adequate supply is also a consideration of great importance in order that the farm home may be provided with the modern conveniences. These so-called "modern conveniences" such as water carriage for dis- posal of sewage, drinking water under pressure and also hot and cold water supplies for lavatory, laundry, and bath have been regarded as obtainable only in the city, and yet all of these sanitary arrangements are readily secured if an adequate water supply is available. Water Supply and Seivage Disposal. 219 Sewage disposal. The disposal of house sewage by water carriage is not only a matter of great convenience but a hygienic necessity. Through the use of the ordi- nary open vault there is not only opportunity for the pol- lution of the well water but the disease-producing bac- teria may be carried from the privy vault to the kitchen, the milk room, and elsewhere by means of the common house fly. If the sewage can be disposed of in a conven- ient way and yet avoid the danger of pollution of water and food much will be done for the comfort and health of the home. Cities that are located on a body of water often dis- charge their sewage into the river or lake. Others less- favorably located find it necessary to dispose of the wastes in other ways, utilizing different methods of puri- fication that shall render the sewage comparatively harm- less. Most of these methods of purification depend on the work of bacteria. The sewage contains organic mat- ter of various kinds, which will be decomposed in the same manner as has been shown to occur in the soil. The final products will be harmless, and in the process of de- composition the disease-producing bacteria will be de- stroyed. The methods of sewage purification seek to establish conditions favorable : (1) for the growth of anaerobic bac- teria that shall render soluble all solid matter contained in the sewage just as the solids are made soluble in the soil ; (2) for the development of the aerobic bacteria that shall complete the work of decomposition, and the nitri- fying bacteria that change the ammonia to nitric acid. Modifications of the types of plants used by cities in the disposal of large quantities of sewage can be used on the farm for the safe and convenient disposal of the 220 Agricultural Bacteriology. house wastes. The cost of such a plant need not be more than the city home must pay toward the construction of the sewers of the city. The conditions that exist on the farms differ so greatly that it is impossible to give a detailed description of a disposal plant that will answer the needs of all farms. In the following description, the essential conditions thai must be established in order to have a successful plant will be given. The house should be provided with a pressure tank, either in the elevated form, or one in which the pressure is maintained by compressed air, so that flushing arrange- ments can be used in the water closets. Septic tanks. The sewage passes from the house drain into a tank in which it is allowed to remain for sev- eral days. The tank can best be made of concrete. It should be placed beneath the ground so as to avoid freez- ing. It should be large enough to hold the accumula- tions of several days, since it is necessary that time be given for the bacteria to decompose the solid matter. A period of four days is sufficient, although a longer time will have advantages. The amount of household sewage will not exceed a barrel per day per person on the aver- age farm. Thus a tank holding thirty to forty barrels will suffice for a family of six persons. The sewage as it passes into the septic tank contains much organic matter in solution and is in condition to serve as bacterial food. The solid matter of the sewage sinks to the bottom of the tank and is rendered soluble by the continued bacterial action. On the surface of the sewage a scum collects which shuts out all air and gives favorable conditions for the growth of anaerobic bacteria. The sewage as it flows from the tank after four or five Water Supply and Sewage Disposal. 221 days exposure is a turbid liquid with a disagreeable odor. The bacterial action is so complete that the solid organic matter is wholly destroyed and scarcely any sediment collects in the tank ; hence it need be emptied and cleaned only at intervals of several years. The tank must be so arranged that a quantity of sewage can be discharged from it at intervals rather than constantly as is the case with the sewage flowing into the tank. The sewage should remain in the tank for a sufficient length of time so that it will no longer putrefy. If this is accomplished, the farther steps in purification and dis- posal can often be very simple. If the septic tank is so situated that a drain can be laid which shall discharge onto the surface of a field that has some fall at a distance from the house, the sewage can be discharged onto the surface of the soil. Since the sewage contains no solid matter it sinks rapidly into the soil, where the purifica- tion is completed. This arrangement can best be used on a sandy or loose soil. The drain should empty into open furrows. Since the tank is arranged so that the sewage can be discharged at intervals the soil has an op- portunity to become aerated between the periods of dis- charge. This avoids keeping the soil saturated with moisture which of course would be detrimental to nitrifi- cation. A preferable process is to discharge the sewage from the tank into drains of ordinary tile laid with open joints. The sewage as it flows from the tank at intervals fills the tile and gradually percolates into the soil through the open joints. On account of the intermittent discharge it has time to drain away and thus favorable conditions for nitrification are maintained. If the sew- age flows into the drains constantly, it would all seep out through the first few joints and keep the soil water- 222 Agricultural Bacteriology. logged. With the discharge at intervals, the entire line of tile is filled and no part of the soil is kept in a satu- rated condition. The tiles should be laid 18-24 inches below the sur- face, the trench about the tile should be filled with cin- ders or gravel so that the water may pass out of the tiles freely. It is not necessary to place the tile below the frost line, although they will be somewhat disintegrated by freezing and the system will have to be dug up more frequently than if freezing did not occur. If the tile are laid too deeply, the amount of oxygen is small and nitrifi- cation is retarded. In a loose, sandy soil, the tile can be laid deeper than in a dense soil and a much shorter line of tile will suffice. By increasing the length of the tile drains, the system will work in a satisfactory manner in a close clay soil. The tile can be laid beneath a cul- tivated field or beneath the lawn since they need be re^ moved and cleaned only at intervals of several years. The essential parts of the system are: (1) a supply of water for the flushing of closets, etc. ; (2) the house so sit- uated that a small amount of fall can be had away from it in order that the septic tank can be emptied into the drains; (3) a septic tank large enough to hold the quan- tity of sewage produced in three or four days so that ample time can be given for decomposition of the solid matter; (4) a method of discharging a quantity of sew- age at intervals. In the accompanying figure the general arrangement of a sewage disposal plant is given. The main drain enters the septic tank below the surface of the liquid so as to avoid disturbing the scum on the surface or the sediment. The* first compartment, the septic tank proper, should hold at least three days sewage and is separated from the Water Supply and Sewage Disposal. 223 second compartment by a partition that does not reach the top of the tank. When the first compartment is filled, the sewage runs over the top of the partition and gradually fills the second compartment. In order to prevent the scum from passing into the second compart- ment a baffle board is bolted to the partition in such a manner that its top is above the level of the scum while its bottom dips into the liquid. Some space is left be- tween the baffle board and the partition. FIG. 22. A SEPTIC TANK. A. drain from the house; B. baffle board to keep the scum (C) from passing into the second compart- ment; D. plug closing the entrance to the drain. At any desired time the second compartment is emp- tied by pulling the plug which closes the opening of the drain. The entire contents of the chamber is discharged into the drain at once. The plug should fit tightly so as to prevent constant leaking of sewage into the drains. The second compartment should be of about the same capacity as the first. An overflow pipe is provided so that if the second compartment becomes full, the tank 224 Agricultural Bacteriology. will not be flooded. The opening of the overflow should" extend to the surface and be protected by a screen, thus allowing air to pass in and out of the drains. The two compartments can be made of different depths if desired. The first can be increased in capacity by increasing its depth; this also serves to aid in main- taining a constant temperature in the sewage. The sec- ond division can be of less depth, thus aiding in obtain- ing .the necessary fall where the slope of the ground is slight. Such a disposal plant will work for a number of years with no attention except the emptying of the second com- partment at regular intervals. If the drains run be- iieath the garden, a constant supply of moisture and of plant food is supplied to the plants. SECTION V. FOOD PRESERVATION AND DISEASES OF PLANTS. CHAPTER XXV. PRESERVATION OF FOODS. All organic matter whether of plant or animal origin is subject to the attacks of living organisms which find in it favorable conditions for growth. The changes in- duced are, in the main, decomposition changes which usually render the material unfit for use as food either by human beings or animals. Food supplies that are to be kept for any length of time must be treated so as to prevent or retard the growth of micro-organisms. This can be done in a variety of ways. Drying. One of the most common ways of preserv- ing organic matter is to dry it, so that the water content is reduced to a point where growth of micro-organisms in or on the material is impossible. The bacteria can grow only in the presence of considerable amounts of moisture. Molds demand much less moisture for their growth, hence many things may be protected from bac- terial action and still be spoiled by the growth of molds. Fodders of all kinds are dried in the field before plac- ing in the barn. If hay or dried forage is not thoroughly dried, it will heat in the mow. The heat is produced by 226 Agricultural Bacteriology. the action of organisms, such as the molds, the same as are concerned in the heating of manures. Ear corn, placed in the crib before it is well dried may likewise mold, although the moisture content is too low to allow growth of bacteria. Various ground-feeds, as meal, readily mold if kept in a damp place. Wheat becomes musty when damp. All of these troubles are caused by the presence of sufficient moisture to allow of mold growth. The preservation of many foods is also made possible by drying, as apples and other fruits, berries, green corn, etc. Meat is also protected from putrefaction in this way. As previously stated, the muscles of a healthy ani- mal are free from bacteria; but in cutting up the carcass the meat becomes contaminated with bacteria and conse- quently undergoes decomposition. If, however, the meat is placed in a dry atmosphere, the outer surface soon becomes so dry as to prevent the growth of bacteria, and as the moist inner part remains free from organisms It does not decompose. If the drying is continued until the entire piece is firm, it will keep for an indefinite period. In South America dried meat is extensively pre- pared and is shipped to all parts of the world. When ground and mixed^ with fat it is a very concentrated form of food and is used where fresh meat can not be procured. Dried milk, or milk powder, and dried eggs are articles of commerce and are extensively used in place of the fresh materials, especially by bakers. The drying of foods usually injures their flavor ma- terially, consequently preservation by desiccation is be- ing replaced, wherever possible, by other methods that conserve the natural flavor to a greater degree. Preservation of Foods. 227 Salting. If certain substances like salt are added to organic matter, they tend to preserve it. Most kinds of bacteria are unable to grow in a saturated solution of common salt. This fact is made use of in the preserva- tion of pork and corned beef, where the meat is placed in a strong brine. If the brine is too weak, certain of the bacteria will grow and the meat will spoil. Such a con- dition is more apt to obtain during warm, than during cold weather. The effect of low temperature, which has a restraining influence on bacterial action, together with the inhibitory action of the salt, exert a more pronounced preservative effect than either of the preservative agents alone. Salt may be applied in a dry form as in the pres- ervation of hides and meats. Smoking. In the preservation of meats such as hams and bacon by smoking, another factor is operative. In the slow combustion of wood, antiseptic compounds be- longing to the cresote group are formed. These are de- posited on the surface of the meat and are absorbed, and together with the salt protect the meat from the action of the bacteria on its surface^. Preservative action of sugar. Sugar, although fur- nishing an ideal food medium for bacteria and molds, may exert a preservative action such as is shown in syr- ups. All solutions containing sugar, as molasses, cane and maple syrups, or fruits conserved in sugar, will not keep unless they are sufficiently concentrated. "Where they undergo a fermentative change they are said to have "worked." The preservative action of sugar in concen- trated solutions depends upon the extraction of water from the bacterial cells causing them to become flaccid or wilted. Under such conditions growth can no longer go on and fermentative action can not follow. 228 Agricultural Bacteriology. Sweetened condensed milk is an illustration of this method of preservation. Part of the water of the milk is evaporated by heating in a vacuum, thereby increasing the density of the milk. The addition of sugar is then made which still further increases the density to a point where bacterial growth is impossible. Such milk may contain living organisms. Dilution of the milk with several volumes of sterile water reduces the concentra- tion to a point where bacterial growth becomes possible and the milk then undergoes fermentation. Fruits are protected from decomposition by placing them in concentrated sugar solutions in the making of preserves. In the preparation, the fruit is cooked so slightly in the sugar that it is not rendered sterile, but the bacteria that are not destroyed ar^ unable to grow in the concentrated medium. Marmalades, jams, and jel- lies owe their keeping qualities to the same factors. Preservative action of acids. The bacteria are un- able, as a rule, to grow in a strongly acid medium. This fact is made use of in the preservation of many foods and even fodders. One of the most common uses of acids in the preservation of foods is in the preparation of pickles with the use of vinegar, which is itself a product of bac- terial action. The acid reaction of the vinegar is so strong that the ordinary bacteria can not grow in it, thus if certain vegetables, as cucumbers, are placed in the vinegar they will be protected against the attacks of bac- teria. Some of the molds find favorable conditions for growth in vinegar, and may destroy so much of the acid of the vinegar as to allow the bacteria present to grow with the result that the pickles are spoiled. Frequently spices are added to the vinegar to be used for pickles, since they improve the flavor. They also have a preset Preservation of Foods. 229 vative effect which is made use of in the preparation of such foods as mince-meat, sausage, etc. In the first, the preservative effect is aided by the sugar present and in the case of sausage by the salt. Fodders such as corn, clover, and other leguminous plants may be preserved by placing them under such conditions that the air can not reach them, as in a silo. In such cases the preservation is accomplished by virtue of the acid which is formed in the tissues as a result of the continued action of the plant cells in the absence of air. The material to be ensiled must have the plant cells in an active condition. Silage can not be made from ripe or frozen corn. In the ensiling of clover it is necessary to place it in the silo before much wilting of the plants has occurred. The living plant cells continue to respire after they are placed in the silo. The supply of free oxygen is soon exhausted and the interspaces filled with nitrogen and the carbon dioxide formed by the respiring plant cells. The cells in their effort to keep alive draw on the oxygen that is found in the sugars and starches of their contents. They are then acting exactly as the anaerobic bacteria when they obtain their supply of oxygen from the sugar in the culture medium. In the effort of the plant cells to obtain oxygen from the materials of the cells, they de- compose the sugar with the formation of lactic and acetic acids and carbon dioxide. These acids are formed in such amounts as to prevent all bacterial growth. The silage of course contains many bacteria that were present on the fodder ensiled, which continue to exist in the si- lage but are unable to grow. The mold spores are also present in the silage but they are likewise unable to grow 230 Agricultural Bacteriology. on account of the lack of free oxygen. The carbon diox- ,ide that is formed in the silage is heavier than the air and does not pass out of the silage, hence, there is no op- portunity for the oxygen to enter from the surface. It the silo is not perfectly tight at the bottom and on the sides, the air will penetrate for some distance, and allow the molds to develop and cause the silage to spoil. If the silage is removed from the silo and placed in a loose pile, the molds at once begin to grow because of the abun- dant supply of oxygen, thus furnished. The plant cells in their respiration produce heat just as the animal does in its breathing. In the case of the living plant, the heat passes off as rapidly as formed. In the mass of material in the silo, the heat produced can not be radiated as rapidly on account of the volume, hence, the temperature of the silage rises to 120 F. or above. This high temperature is retained for a long time and prevents the freezing of the silage, a very for- tunate circumstance without which it would be very diffi- cult to use this method of preserving fodder in the north. If the plant cells are dead because the plant is ripe, or because of being frozen, the oxygen of the air in the silage is not used, and molds are able to grow. Acids are not formed by the decomposition of the sugars and consequently various kinds of bacteria are also able to grow. The result is a rotten mass instead of a fermented, but succulent and nutritious feed. It is desirable to al- low the corn to become \vell matured, as the silage formed is not as acid as is that prepared from the more immature corn. This is due in part to the difference in the compo- sition of the plant at different stages. If the corn or clo- ver is somewhat wilted, the cells cannot respire even though they are not dead. If water is added to the silage Preservation of Foods. 231 as it is placed in the silo, the cells are revived and normal silage is formed, when without the addition of water the silage would spoil. In the preparation of sauerkraut the fresh tissue is treated in very much the same way as is that placed in a silo, except that salt is added and the cabbage is packed until the interspaces are filled with liquid instead of gases as in silage. In this weak brine, acid-producing bacteria grow, apparently forming from the sugar and starches of the cabbage, lactic and acetic acids, that prevent the growth of the putrefactive bacteria. Sauerkraut is usu- ally stored in open vessels. On the surface of the acid liquid, molds grow which gradually neutralize the acid. At last a point is reached where the putrefactive bacteria can begin to grow. The sauerkraut then changes into an offensive mass of decomposing tissue. Preservation by canning. In many of the processes of food preservation, the product is less appetizing than the fresh material. In order to avoid this as far as pos- sible, the process of preservation by canning has been introduced. In the canning of most materials the bac- teria are absolutely destroyed by heating where the ex- posure is made either at the boiling point of water for a considerable period or for a shorter period of exposure at higher temperatures. In the canning of corn, peas, meats, fish, etc., the latter process is employed. The- canned foods are sterile and will keep for an indefinite period. In the canning of very acid vegetables, as to- matoes, it is not necessary to render them perfectly free from living bacteria, as the acid prevents germ growth. If the heating is sufficient to kill the mold spores, yeasts, and bacteria that do not form spores, the tomatoes will keep. Some bacterial spores will be left but they can not 232 Agricultural Bacteriology. germinate on account of the acid reaction of the toma- toes. Corn, peas and nonacid vegetables must be made absolutely free from all organisms. This is often quite a difficult process in the household, hence these are han- dled with less success than are the acid vegetables like tomatoes. Preservation by cold. In the modern methods of food preservation, low temperatures are constantly em- ployed. All kinds of foods are placed in cold storage. If the temperature is above the freezing point as must be used with certain kinds of foods, the bacteria grow slowly. If the material is such that the temperature can be reduced below the freezing point, the growth of bac- teria will be prevented. Butter and meats are stored at temperatures far below the freezing point. Eggs and fruits must be kept above freezing. Preservation of eggs. Fresh eggs soon deteriorate in quality due to the growth of organisms that cause the egg to spoil. Infection of the egg may occur in the ovi- duct of the hen before the shell is developed. Also, owing to the porous nature of the shell, bacteria may work their way through it into the white of the egg which affords them an excellent food medium. A number of methods have been devised whereby the keeping qualities may be enhanced. These methods are of much practical value as they enable the surplus eggs of summer to be held and disposed of at more profitable prices in winter when fresh eggs are scarce. The first step in all processes of preservation should be to keep the eggs clean by maintaining clean straw or other material in the nests. The most successful way of keeping the eggs is by placing them in a solution of water glass (sodium silicate). This compound can be procured Preservation of Foods. 233 at many drug stores. It costs from one dollar to one dol- lar and a quarter per gallon. The preserving solution is prepared by adding to nine parts of water that has been boiled and allowed to cool, one part of the water glass mixing the solution thoroughly. The eggs should be placed in the solution within twenty-four hours after they are laid. It is claimed that April, May and June eggs keep better than do those laid later in the summer. It is advisable to use July and August eggs first when eggs from all of the months have been preserved. The eggs should be examined before placing them in the solution to see that they are clean and are not cracked. The stor- age room should not be above 60 F. and should be as uniform in temperature as possible. Preparation of vinegar. Fruit juices, as apple juice, undergo a spontaneous fermentation. There are present on the surface of the fruit, yeasts which find favorable conditions for growth in the juice. These change the sugar to alcohol as in the preparation of cider and wine. If these liquids are allowed to stand exposed to the air, they usually undergo, spontaneously, what is known as the acetic fermentation in which, by the action of the acetic acid bacteria, the alcohol is changed to acetic acid. The bacteria causing this change are aerobic and grow only on the surface of the liquid. It is therefore advisa- ble to have the cask only partially filled with the liquid. The acetic bacteria grow most rapidly at 70 F. It re- quires a number of months (12-18) to complete the proc- ess of acetification. The process may be hastened some- what by adding to the cider or wine a quantity of mother- of- vinegar which is simply a mass of acetic acid bacteria. After the process is completed the casks of vinegar should be completely filled and stoppered tightly in order to pre- 234 Agricultural Bacteriology. vent the growth of aerobic bacteria that destroy the acetie acid and thus weaken the vinegar. A more rapid process is known as the Orleans process, in which dilute solutions of alcohol are allowed to trickle over beech wood shavings. This brings the liquid in inti- mate contact with the air and after the shavings once be- come seeded with proper bacterial growth, the conversion of the alcohol solution to acetic acid occurs very rapidly. CHAPTER XXVI. BACTERIAL DISEASES OF PLANTS. Bacteria, as a rule, grow best in food substances that are alkaline in reaction, while other fungus plants, molds, rusts, apd mildews, find most favorable conditions in an= acid medium. The juices of the animal body are alka- line, those of plants are usually acid. These facts have been usually regarded as the explanation of the greater susceptibility of plants to diseases caused by fungi other than the bacteria. Very few important diseases of ani- mals are produced by molds, and, conversely, few bac- terial diseases of plants are of great economic importance. Another reason for the greater prevalence of bacterial diseases in animals is that the invasion of the animal body by bacteria is made possible through the natural openings of the body. The invasion of the plant tissue is more dif- ficult since there are no natural openings comparable to those of the animal body. The diseases of plants caused by rusts, mildews, smuts, etc., are of the most varied nature and affect all kinds of plants. Methods of prevention through the use of solu- tions applied to the seed as in the treatment of oats and barley with formaldehyde or hot water in order to de- stroy the smut spores on the grain, or the spraying of fruit trees to destroy the fungi thereon, are widely and successfully used. A number of bacterial diseases of plants have been studied. The knowledge concerning many of them is 236 Agricultural Bacteriology. incomplete and methods of prevention can, therefore, not be so successfully used as in the case of diseases caused by other fungi. Pear blight. A disease that is most common in the pear is known as blight, or fire blight, since the diseased parts appear as though they had been injured by fire. The disease affects apple, quince, apricot, and plum trees. It is said to affect the mountain ash and several species of hawthorne. The bacteria enter the tissue most FIG. 23. PEAR BLIGHT. The bacteria causing the shriveling- of the fruit en- ter through, the blossom. often through the blossom, being carried from flower to flower by bees and other insects. They may also enter through wounds on any part of the tree. The bacteria grow in the inner bark, gradually working their way down the twig, causing the leaves to turn brown and to become dry, and the bark to blacken and shrivel. The growth may extend to the trunk and the tree be de- stroyed. The growth of the bacteria in the tree is most rapid in the spring and summer while the new tissues are tender Bacterial Diseases of Plants. 237 and full of sap. By midsummer the progress of the disease is checked by natural causes. The bacteria may pass the winter in the affected tree and with the advent of warm weather begin to grow once more. It is claimed that trees in a thrifty condition and that are making a large amount of growth are more susceptible to attacks than trees under less favorable conditions. Prevention. Since the bacteria are protected by the bark nothing can be done to destroy them by the use of spraying solutions. The only method of preventing the spread in the tree is by the removal of all affected branches which should be cut off several inches below the last visible signs of disease as the bacteria extend beyond this point. The diseased wood should be burned, other- wise the bacteria may be carried to still healthy trees by insects. Care should also be exercised not to spread the disease through the pruning or grafting knife. Cabbage rot. The cruciferous plants as cabbage, cauliflower, turnips, etc., are subject to rots caused by bacteria. The most common method of infection of the plant is through the small water pores on the edge of the leaf. They may also enter through wounds such as are made on the roots at the time of transplanting. It has been shown that the seed may be infected; in this way the soil of the seed bed is inoculated with the bacteria and opportunity is offered for infection of the young plants. The bacteria will persist in the soil of a field or seed bed for a number of years, hence it is advisable not to use the same^ field or bed when the disease has ap- peared. Seed may be rendered free from the cabbage rot bacteria by soaking it in a one to one thousand solution of corrosive sublimate for fifteen minutes. The disease appears first in the form of brown spots on 238 Agricultural Bacteriology. the edges of the leaves. The spread of the disease in the plant is along the veins and ribs to the main stem. On cutting across the stem of an infected leaf one can see the blackened ends of the fibrous strands (fibro vascular bundles). The channels that carry the food and water supply of the leaf are destroyed ; the leaf is thus deprived of nourishment and dies. Efforts to combat the disease in the field by the re- moval of diseased leaves have proved unsuccessful. Preventive measures must be confined to a treatment of the seed and to the growing of cabbage in a system of ro- tation rather than on the same field continuously. Melon wilt. Squash, cucumber, and melon vines are subject to a bacterial disease known as wilt since the af- fected tissues are wilted, due to the plugging of the water tubes with the bacteria. The disease is most prevalent in the early summer and is easily told from all other troubles of the melon family by the sudden wilting of the leaves without any other visible symptoms. The bacteria live in the soil and gain entrance to the plant through wounds. It is undoubtedly spread from plant to plant by means of the various insects that feed upon the vines. The only means of prevention is to grow melons and squash in rotation with other crops. INDEX. Abortion, contagious, 147. Acids, preservation of foods by, 228. Acidity produced in milk, 54. Actinomycosis, 142. Aeration of milk, 48. Aerobic bacteria, 8. Air, bacteria in, 14; contami- nation of milk from, 33. Alcoholic fermentation of milk, 60. Ammonification, 187. Anaerobic bacteria, 8. Anthrax, 98; spread of, 103; vaccination against, 101. Antiseptics, 12; in milk, 48. Antitoxin for tetanus, 132. Azotobacter, 205. Bacteria, aid in animal diges- tion, 208; colonies of, 18; determination of number of, 17; distribution of, 13; forms of, 2; in soil, 174; nature of, 1; pure culture of, 19; reproduction of, 3; size of, 3; structure of, 2. Barn air, 33. Bitter milk, 61. Black leg, 104. Butter, 65; deterioration of, 70; flavor of, 65; moldy, 72; sour-cream, 65 ; sweet- cream, 65; undesirable fla- vor In, 71. 'Cabbage rot, 237. 'Calcium, 182. Canning, preservation of foods -by, J231. Carbon, cycle of, 181. Carbolic acid, 168. Cellulose digestion of, 208. Certified milk, 83. Cheese, 73; Cafnembert, 80; Gorgonzola, 79; Limburger, 80; ripening of, 75; Roque- fort, 79; Stilton, 79; Swiss, 78; types of, 73. Chicago, rules for production of milk, 85. Chicken cholera, 157. Cold, effect on bacteria, 10; preservation of foods by, 232. Colored milk, 62. Copper sulphate, 169. Corn stalk disease, 109. Corrosive sublimate, 169. Cows, cleaning of, 28; clipping of, 28; tuberculosis of, 39. Cow pox, 146. Cow stalls, 27. Cream, ripening of, 66, 69. Cresol, 168. Culture, media, 15. Denitrification, 190. Diphtheria, bacteria of in milk, 40; of fowls, 159. Dirt in milk, 26. Disinfectants, 12. Disinfection, 165. Distemper of dogs, 163; of horses, 163. Drying, preservation of foods by, 225. Eggs, preservation of, 232. 240 Index. Factory by-products, 31. Farcy, 129. Farm separators, 31. Feed, effect of on bacteria in milk, 34. Ferrous sulphate, 169. Fermentation of milk, 53. Fire blight, 236. Foods, preservation of, 225; preservation of by drying, 225; preservation of by salting, 227. Foot and mouth disease, 162. Foot rot of sheep, 162. Fore milk, 25. Formaldehyde, 169. Fowl, cholera of, 157; diseases of, 157; roup of, 159; tu- berculosis of, 126; typhoid, 159. Fungi, 1. Immunity, natural, 95; artifi- cial, 95, 102. Intestines, bacteria in, 14. Intestinal diseases, caused by milk, 42. Garget, 144. Germicides, 12. Glanders, 127; diagnosis of, 130. Gorgonzola cheese, 79. Heat, effect on bacteria, 11. Hemorrhagic septicemia, 107. Hog cholera, 151; prevention of, 154. Hogs, diseases of, 151; tuber- culosis of, 125. Horses, distemper of, 163. Hydrophobia, 136. Lactic acid bacteria, 54. Leguminous plants, 198. Lesions of disease, 96. Life in soil, 177. Limburger cheese, 80. Lime, 167. Lumpy jaw, 142. Mallein test, 130. Mammitis, 144. Manures, bacteria in, 207; de- composition of, 209; fire fanging of, 211; losses from, 210; in milk, 26. Market milk, 82. Mastitis, 144. Melon wilt, 238. Microscope, 20. Milk, abnormal fermentation of, 57; aeration of, 48; al- coholic fermentation of, 60; bacteria in, 90; bitter, 61; care of, 89; certified, 83; clarifying of, 46; colored, 62; commissions, 83; con- densed, 52; contamination of, 23; cooling of, 46; dis- ease-producing bacteria in, 38; filtering of, 45; gassy fermentation of, 56; house, 37; market, 82; pails, 28; pasteurization of, 49; poi- soned, 43; preservation of, 44; slimy, 58; souring of, 53; straining of, 44; tuber- cle bacteria in, 39; utensils, contamination from, 29; utensils, washing of, 32. Milker, contamination of milk from, 34. Milking, 88. Minerals, action of bacteria on, 182. Nitrification, 187; conditions favoring, 188. Nitrogen, conservation of, 192; fixation of, 196, 204. Nodular disease, 126. Nodules on legumes, 199. Odors, absorption by butter, 72; by milk, 36. Organic matter, decomposition of, 178. Parasitic bacteria, 7. Pasteurization, 49, 87; of cream,. Index. 241 Pathogenic bacteria, spread of, 95. Pear blight, 236. Period of incubation, 96. Pickles, 228. Phosphorous, 182. Plants, bacterial diseases of, 235; leguminous, 198. Plant food, 171. Poll evil, 162. Potassium, 185. Preservatives. 12. Rabies, 134; diagnosis of, 139; prevention of, 138; symp- toms, 135. Roquefort cheese, 79. Roup, 159. Salting foods, 227. Saprophytic bacteria, 6. Septic tank, 220. Septicemia, 107. Sewage, disposal, 219; purifica- tion, 219. Silage, 229. Slimy milk, 58. Soil, bacteria in, 13, 174; inocu- lation of, 202. Spores, 5, 58. Stable, disinfection of, 169. .Starters, home-made, 66; pure- culture, 68. Sterilization, 16. Stilton cheese, 79. Sugar, preservation of foods by, 227. Sulphur, 185. Sweet curdling of milk, 57. Swine plague, 156. Swiss cheese, 78. Symptomatic anthrax, 104. Temperature, of cows, 120; ef- fect on bacterial growth, 9. Tetanus, 131. Transmissible diseases, 88, 92. Tuberculosis, 86, 110; diagnosis of, 118; distribution of, 110; of fowls, 126; of hogs, 125; symptoms of, 117. Tuberculin test, 118. Typhoid fever, bacteria of in milk, 40; of fowls, 159. Udder, contamination of milk from, 24. Utensils, milk, 89. Vinegar, 233. Water, 90; bacteria in, 13; dis- ease-producing bacteria in, 215. Water glass, 232. White scours, 161. Wisconsin curd test, 63. Yeasts, 60. UNIVERSITY OF CALIFORNIA -,, <. foXxj LIBRARY 201935 THE UNIVERSITY OF CALIFORNIA LIBRARY