sete ets? Sars ~6- 9-8-4 —@~ 4 — @—@ 0-8 Se PE PR a hel “Fa 9 Fs Pete a eee seen Stats wera te aa eater prot mbt el Fat teat tee oe ripe at tt ie aoe pia ee ; : = eee ; : rsa pee ee ete ete : EST ceed pre ed pS phen pee eee eel eet ere eee re eres 12 ApS ees a ieeree tae tt 1chy Sia eid fj ye) ats atta deme mores ef wre od Porta Bie 4 i = Ge. eam Weta paw ee eel rere PARC A eeeree ra et tS - eastern sas = aoe = ? ere Pear rere et re ee et ee sates re Cees eee nace a felettes Peeper eee eet SSgtetats. a Orr re Cope Stern et os rae eT Sir pe Mey Ay art Par er tert Lr Sere eee Set ee, it esecin oe =. Cornell Mniversity Library BOUGHT WITH THE INCOME FROM THE SAGE ENDOWMENT FUND THE GIFT OF Henry W. Saqe 1891 que td ais. 9724 RETURN TO ALBERT R. MANN LIBRARY ITHACA, N. Y. Cornell lea Library QR 56.C72 1912 mi d molds in the home, IN mann Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http :/Awww.archive.org/details/cu31924003199332 BACTERIA, YEASTS, AND MOLDS IN THE HOME BY ‘s v Ne \ y He W:' CONN, Pu.D. Proressor oF BioLoGy In WESLEYAN UNIveERSITY, MIDDLETOWN, Conn AUTHOR OF “‘AGRICULTURAL BACTERIOLOGY,” “ BACTRRIA IN MILK anpD 1Ts Propucts,” “THE Story or GERM Lire,” ‘THe Meruop or Evo.ution,” etc. REVISED EDITION GINN AND COMPANY BOSTON - NEW YORK - CHICAGO . LONDON ENTERED AT STATIONERS’ HALL CopyRIGHT, 1903, 1912 By H. W. CONN ALL RIGHTS RESERVED 913.8 The Athenaum Press GINN AND COMPANY « PRO- PRIETORS + BOSTON « U.S.A, PREFACE The rapidly growing interest in home economics is caus- ing this subject slowly to assume the aspect of an exact science. At the present time it is becoming necessary for those expecting to become housewives to understand at least the elementary phases of a number of sciences, most prominent among which are chemistry and bacteri- ology. The relation of microdrganisms to household affairs has only been recognized in the last few years, but is now felt to be one of the most important phases in the study of the problems of the household. The present work is therefore designed for all interested in household affairs, including not only students of household econom- ics but all persons who have practical charge of homes and are. interested in keeping them in the best and most healthful condition. TABLE OF CONTENTS CHAPTER Pace I. INTRODUCTION . ‘ 3 ‘ ‘ : : - I SEcTION I— MOLDS Il. THE GENERAL NATURE OF MOLDS : 3 é 12 III, CONDITIONS FAVORING MOLD GROWTH . : 32 IV. THE Decay or Fruit; Userut Moxtps; MoLp DISEASES é i 3 “ 5 . 5 40 SEcTION II — YEASTS V. YEASTS AND THEIR DISTRIBUTION . ‘ - - 56 I. YEASTS IN THE HOUSEHOLD . : . ‘ 7 68 II.) BREAD RAISING; FERMENTED LIQUORS . : . 86 Section III— BACTERIA VIII. THE GENERAL NATURE OF BACTERIA. , 7 100 IX. BACTERIA WHICH LIVE UPON DEAD Foop é . 124 X. THE PRESERVATION OF Foop; DRYING; COOLING 139 XI. THE USE OF PRESERVATIVES F . - 157 XII. PRESERVATION BY CANNING . : ‘ B : 169 XIII. MiLk; EGGs; PTOMAINE POISONING : : . 182 XIV. DISEASE BACTERIA ‘ : : . . : 203 vi CONTENTS CHAPTER Pace XV. PREVENTION OF DISTRIBUTION OF CONTAGIOUS DISEASES . 5 eRe A Fi é ~ 212 XVI. PRACTICAL SUGGESTIONS : . : . 242 XVII. DIsINFECTION . . . , ° 5 , . 256 APPENDIX DIRECTIONS FOR LABORATORY EXPERIMENTS . ‘ : 269 INDEX . ° ° ° ° ° : ° e ° . 289 BACTERIA, YEASTS, AND MOLDS CHAPTER I INTRODUCTION Bacteria, yeasts, and molds comprise a series of plants commonly known as microorganisms, or more popularly as microbes. It has for some time been recognized that together they form a group of the utmost importance not only to the physician but also to the agriculturist. To-day it is beginning to be appreciated that their rela- tion to the ordinary household, and hence to the house- wife, is even more intimate than to the physician. We are learning that many of the tasks of the housekeeper, some of which may be more or less unpleasant, have their foundation in bacteriology, and we are beginning to recog- nize that these microdrganisms constitute the foundation of the demand for cleanliness so forcibly emphasized in modern times. In the household microdrganisms have an important bearing in three directions: 1. They are the cause of the decay and spoiling of foods and many other products. 2. They are sometimes of value in the preparation of foods. 3. They are the cause of contagious diseases. I 2 BACTERIA, YEASTS, AND MOLDS 1. MICROORGANISMS AND THE PRESERVATION OF FoopD Although household duties are varied in character, the larger part of them concern the preparation and the pres- ervation of foods. The preparation of food belongs pri- marily to the department of cooking, although certain other factors are concerned. But the science of cooking has little to do with the preservation of food. This latter problem is intimately related to modern bacteriology. It is largely for this reason that the study of bacteriology and kindred subjects has in recent years come to be looked upon as a part of the necessary training of the housewife. At the outset we may properly ask, Why is it that food spoils? Why will not food keep indefinitely without the many contrivances designed to prevent its spoiling? The answer to this question is, briefly, that other living things besides ourselves are fond of the same foods of which we are fond, and that these other living beings take every occasion to consume the material which we design for our own food. Preserving the food in our pantries, cellars, and refrigerators, therefore, simply means protecting it from consumption by other living organisms; and if we can keep these organisms away, food may be indefinitely preserved. On the other hand, if we cannot protect our food from the attack of these organisms, it spoils; for the spoiling of food is simply the result of its consumption by living beings for whom we have not designed it. The living beings that endeavor to consume our food comprise, in the first place, some of the larger animals with which every one is familiar. Every one knows about PRESERVATION OF FOODS 3 rats and mice, and the various insects in the home are only too familiar pests. But not every one understands that in addition to these large animals there is a great host of plants and animals which seize every opportunity of feeding upon that which we intend for our own use. All such small animals and plants go by the general name of microbes or microorganisms. We are chiefly concerned, in this book, with three important groups of plants. Some of these plants are large enough to be seen easily and are generally well known, such as the molds that occur everywhere, and are always regarded as nuisances in household economy. In addition to the visible plants there is a still larger num- ber of others, quite too small to be visible to the naked eye and, indeed, only seen with the high powers of the microscope. These invisible organisms are the smallest living beings of which we have any knowledge, and are both friends and foes. Not only are they invisible to the naked eye but to the ordinary housewife they are quite unknown. Until within recent years they have been unknown even to scientists, and although science has now learned to understand quite well what they are and what they do, to the public in general they are little more than a name around which cluster various mysteries and in regard to which there is no general information. Molds and yeasts have long been known. The term bacteria is new, and refers to organisms just beginning to claim public attention but in regard to which there is at present a large amount of misunderstanding. But even though they are very minute, and though she knows little about them, the housewife finds them the most serious, indeed 4 BACTERIA, YEASTS, AND MOLDS the only serious foe with which she has to contend in her attempt to keep food in proper condition for use. These invisible plants are constantly on the alert to con-. sume for themselves the foods which the housewife designs for the table. If they have a chance to get at the food, she soon notices that it undergoes a series of changes, characterized by what we call putrefaction, decay, souring, or perhaps some other change not properly classed under any of these terms. The general rotting of fruit, the decay of meat, the souring of milk, and a host of other similar phenomena which occur in every pantry if the food is not carefully protected, represent some of the effects produced in foods when microérganisms begin to feed upon them. Thus it is evident that these microscopic plants play a very great part in domestic economy. This fact, however, has not been thoroughly appreciated until recent years, and indeed it is only just beginning to be recognized to-day that the housewife’s knowledge should comprise an understanding of the nature and hab- itat of these microscopic foes, their methods of distribu- tion from place to place, the conditions under which they grow and fail to grow, together with the various devices which may be adopted for checking their active growth where they are not wanted. Although the facts have only recently been appreciated, it is known to-day that a very considerable part of the duties in every household is concerned with these microscopic organisms, known and unknown. The chief desire of the housewife is to prevent the growth of these microorganisms in places where they are not wanted. For this purpose have been invented MICROORGANISMS AS USEFUL AGENTS 5 refrigerators and all devices for cold storage and for cool- ing and keeping cold any food products ; to this end, too, are designed the various methods of preserving food and fruits. The immense industry of canning, either on a large scale as is done in factories, or on a small scale as is done in the household, is dependent upon the relation of microédrganisms to food. The sterilizing or pasteuriz- ing of milk, as well as other foods, is also a bacteriological problem, and, indeed, many other phases of household life are really bacteriological phenomena. Whether or not she possesses a scientific knowledge of bacteria and their allies, the housewife must have a certain practical knowledge of their nature and of their powers, for this practical knowledge is absolutely necessary to enable her to preserve her food successfully from the microérganisms which are so liable to spoil it. 2. MICROORGANISMS AS USEFUL AGENTS It must not be understood, however, that micro- organisms are always our foes. It is true that in the household they are commonly a source of trouble, but it is also true that some of them are distinctly friends. To appreciate that they are sometimes useful, even in our foods, one needs only to remember that under this head are included the great group of yeasts that play such an important part in the household in the raising of bread and in all types of fermentation. Yeasts, as well as bac- teria, are microscopic plants, of which the microscopist recognizes many kinds. Some of these are troublesome, but, so far as concerns their relations in the household, 6 BACTERIA, YEASTS, AND MOLDS they are useful servants rather than undesirable foes. Even bacteria, which are in general looked upon as dreaded foes, and as agents only of evil, are, under some circumstances, our friends rather than our enemies. Bacteria, for example, produce the delicate flavors in butter and the stronger but equally delicious flavors of cheese. Bacteria also are solely responsible for the man- ufacture of vinegar; for although vinegar might be made by chemical means, the vinegar of our tables is produced by the agency of bacteria. Molds also, though generally looked upon as unmitigated nuisances, are, in some places, of decided use. The utility of molds, however, has little to do with household products, being confined chiefly to the production of certain types of cheeses. The flavor of Roquefort cheese, for example, is due chiefly, if not wholly, to the growth of certain types of molds within the cheese. These illustrations will serve to show that microérganisms, even in the household, must occasionally be looked upon as friends rather than enemies. 3. MICROORGANISMS AND DISEASE Certain species of microérganisms are harmful to human health and are the cause of contagious diseases. They are generally known as disease germs or pathogenic bacteria. Fortunately they are few in number. While large numbers of species of microérganisms may be troublesome in the household because of their action upon our foods, very few species, comparatively, are able to do harm in the human body or to produce disease if they should find entrance. The great majority of species MICROORGANISMS AND DISEASE 7 are, then, harmless to human health, but a small number are capable of producing disease, and for this reason are of especial interest. The study of the causes and cure of disease belongs primarily to the physician and not to the housewife. The housewife must, it is true, occasionally act as the nurse of persons suffering from contagious diseases, and will then be interested in the treatment of the patient and the cure of the disease. But even here the question of cure must be left to the medical profession, while as nurse she should simply follow the directions given. Yet one phase of the matter is almost solely hers, for to her must be left the task of preventing the distribution of contagious diseases. Many of the diseases produced by microérganisms are distinctly contagious and, unless the patient and the other members of the home are properly guarded, a disease is likely to be carried through a household from one person to another. To prevent the distribution of such contagious diseases is the duty of those who care for the home. , The problem of preventing the distribution of various diseases is a bacteriological one, for, inasmuch as bacteria are usually the cause of the disease, the prevention of contagion is the prevention of the distribution of bac- teria. In every home such problems are more or less com- mon. They concern the members of the home far more materially than they do the physician. Every household will occasionally have experience with contagious diseases, and the question of preventing their distribution from a patient to a healthy individual is sure to arise. The house- wife who cares for the home year after year will have 8 BACTERIA, YEASTS, AND MOLDS many experiences where a knowledge of distribution of diseases is of even more importance to her than to the physician himself. The physician is directly concerned in the cure and only indirectly in the prevention of contagion ; the housewife must always have upon her shoulders the duty of keeping her family in health, and when an instance of contagious disease appears she must try to protect the rest of the household. For these reasons it follows that a knowledge of disease germs is of more vital significance to one who cares for the home than it is to the physician, who is only concerned in curing the disease. The physi- cian or the Board of Health may give suggestions and directions, but the successful application of these direc- tions depends upon the intelligence of the home keeper. This brief outline of the relation of bacteria to various household problems is sufficient to show why a knowledge of microdrganisms should be a part of the equipment of any one who is to conduct the affairs of a well-regulated household. For the development and preparation of some foods, for the preservation of all foods, and for the pro- tection of the health of those under her care, the head of a modern well-equipped home needs to understand bac- teria and kindred organisms. A knowledge of molds, yeasts, and bacteria has become a vital if not a necessary part of training in domestic economy. DIFFERENT CLASSES OF MICROORGANISMS The microérganisms with which we are concerned all have one common characteristic : they are what botanists call colorless plants. ‘This does not mean that they are CLASSIFICATION OF MICROORGANISMS 9 absolutely without color, for they may be bluish, reddish, gray, or white, or, indeed, they may show other colors; but it means that they do not have the green color char- acteristic of the majority of plants in nature. The absence of this green coloring makes them unable to live upon the food in the soil, and forces them to live upon a kind of food different from that of ordinary plants. Ordinary green plants can live upon minerals which they obtain from the soil, and upon gases which they obtain from the air, but the colorless plants cannot use such materials at all. They need a more complex type of food. The materials in nature are frequently divided into mineral and organic substances. Mineral, or inorganic, sub- stances are such materials as rocks, sand, earth, etc. Organic substances (wood, bones, fruit, muscle, etc.) are those which have been produced by animals or by plants, i.e. by oxganisms. Evidently the foods we eat — meats, fruits, vegetables, etc. — are organic, since they all come from plants or animals. The colorless plants —the Fungi — are, like animals, obliged to have organic sub- stances for foods, and therefore feed upon materials essen- tially similar to those which form the food of animals, i.e. meats, fats, sugars, etc. Since the colorless plants and the animals are in need of the same kinds of food they become rivals in nature. The green plants, on the other hand, living upon totally different foods, are in no sense the rivals of animals, but their allies. It is this fact, their living upon organic foods, that makes the colorless plants of so much importance for good or ill, and explains their close relation to the problems of the household with which we are concerned. 10 BACTERIA, YEASTS, AND MOLDS Botanists class all colorless plants under one general group, which they call Fungi. Under this group is a large variety of plants which show wide differences of structure in size and general appearance. But inasmuch as they all agree in lacking green coloring material, they are, at least from the standpoint of their relations in nature, prop- erly placed in one general class. The group of fungi as recognized by botanists is subdivided into a number of divisions. A method of dividing them, convenient for our purposes, is as follows. FunNGI Higher Fungi. This includes the forms of large size, known generally as mushrooms, toadstools, wood fungi, rusts, sneuts, etc. With these plants we are not particu- larly concerned in the household. Molds. Fungi of considerable size, easily visible to the naked eye, composed of threads. Yeasts. Microscopic plants which multiply by a pro- cess called budding, composed of oval bodies. Bacteria. Still smaller plants that multiply by a pro- cess called fission, composed of spherical, rod-shaped, or spiral bodies. This classification is not scientifically accurate. The higher fungi include a large number of different types classed by botanists into many subdivisions. But since they are not concerned in household problems we may most conveniently group them together and consider them no further. The group of molds also is not a proper scientific divi- sion, since under this head are included several different CLASSIFICATION OF MICROORGANISMS II kinds of plants which botanists agree must be separated into several divisions. Some of the so-called molds really belong to the higher fungi. But though the term “mold” is not a good scientific one, practically it is very useful. It is a common English word, quite generally understood, and always refers to a variety of plants characterized by a general appearance so well known as to be easily recognized by persons who are entirely unfamiliar with scientific botany. Although admitting that the molds do not represent any real scientific division of fungi, we may use the term as referring to colorless plants which every one recognizes but which cannot be scientifically defined. The other two groups, yeasts and bacteria, are proper scientific divisions. In our study of household problems we are concerned only with molds, yeasts, and bacteria. SECTION I— MOLDS CHAPTER II THE GENERAL NATURE OF MOLDS As intimated in the last page, the group of molds does not form a scientific division. Among the plants grouped under this popular name are included representatives of several different groups of fungi. The general character of molds is a dense mass of fine white threads. But some of the higher fungi related to the toadstools produce a white threadlike mass, and if we find this growing in abundance upon the surface of wood we commonly call ita mold. Other so-called molds belong to the different subdivisions related to cup fungi, Ascomycetes, while still others belong to an order of fungi which includes parasitic . plants like rusts and smuts, and are called Acidiomycetes. We must not, therefore, look upon molds as a division which would be recognized by any botanist. For house- hold purposes, however, no term can take the place of this. one, so universally known and so thoroughly understood. In our studies, therefore, we shall group together as molds all types of fungi which produce white felted threads, which have the power of growing in or upon food materials, and which give rise to the well-known appearance that char- acterizes the plants going under this common name. Most of them are closely related to each other. 12 THE GENERAL NATURE OF MOLDS 13 The general appearance of molds is well known to every one. At first they are soft, fluffy masses, usually white, though later they may become blue, green, brown, black, or red. They grow upon all sorts of material and, under some conditions, with very great rapidity. A typical mold as it appears to the naked eye is shown in Fig. 2. The molds which are liable to appear on the foods in the household are by no means always alike,though the house- keeper rarely recog- nizes any difference between them. They differ in many respects, —in the fineness of the threads of which they are made, in the rapidity of their growth, in the mate- Fic. 1. Two colonies of common mold, A ; Penicillium, as shown under the micro- rials upon which they scope on a black background. grow, and more partic- ularly in color; for while most are white at first, they show many other colors later. The most common of the house- hold molds is one which at the time of fruiting becomes a bluish-green color, and hence is called the “blue mold,” Penicillium glaucum (see Figs. 1 and 5). This species is common upon bread and cheese, but it will grow upon 14 BACTERIA, YEASTS, AND MOLDS Fic. 2. A piece of bread upon which one of the common molds (AZucor) is growing. Fic. 3. A common mold, Mucor, growing on a bit of banana, THE GENERAL NATURE OF MOLDS 15 leather, as well as upon a host of other materials. We frequently find upon other foods, especially fruits, two or three kinds of brown molds, and some that even when fruiting remain pure white. Some, again, become pretty Fic. 4. The sprouting of the spores of Penicillium... At 6 there is a-cluster of. seven _ Spores sprouting to form a colony. * wie : néarly black, while still mayest others.’ grow red or, pink. / of spores of an One of the very. common older colony. forms consists of a rather yy, 5. The growth from two spores coarse: mass’ of threads, two days later than Fig. 4, showing ‘upon. which ‘develop the beginning of the formation of saat aay ‘ Gel: spores, showing method of origin at numerous © rounded blac nee balls ‘about the size of a period, while another consists of delicate threads with clusters of white.spores looking like snowballs. Each of these different colors indicates a different species of mold. There are scores of species known to botanists, but it is quite unnecessary for the housekeeper to attempt to dis- tinguish them: » Pieces of moldy lemon, banana, apple, and bread will be quite sure to show different species of molds. 16 BACTERIA, YEASTS, AND MOLDS SrrucTURE oF MoLps It requires microscopic study to make out the structure of molds, but it is important to understand this structure in order to be able to explain the conditions under which they grow. If we study a young mold before it has begun to produce its fruit, it is found to consist of a long, highly branching thread (Fig. 5). When it begins to grow all that can be seen is this tangled mass of delicate threads. The threads are so minute, as a rule, that the individual fibers are only just large enough to be seen by the naked eye, and in many cases they are too small to be seen except with a lens. The thread of the blue mold is too small to be seen without a microscope. The threads are practically always of a whitish color, nearly transparent when examined under the microscope, and appear as shown in the several figures. In some species of molds they grow into a very dense, felty, rather tough mass. In other species they form a loose mass of coarser fibers (Fig. 2). An important point to be remembered is that these threads, by their growth, can penetrate into the depths of the material upon which they are growing. If they are upon the surface of bread, the fine fibers push their way down into the substance of the bread. If they grow upon cheese, the threads force their way into the body of the cheese. When growing upon any soft food material, the mold threads, though visible only on the surface, really extend into the substance for a considerable distance, although they are so small and transparent that we cannot follow them. Of course the readiness with which a mold THE GENERAL NATURE OF MOLDS 17 can grow through food material will depend upon the tough- ness or firmness of the material. Upon damp leather the thread is not capable of growing underneath the surface so readily as it can upon bread. This thread is known to botanists by the term mycelium, and by this term we shall hereafter refer to it. The young mold is a white, loose mass of mycelium, but as it grows older it becomes denser by continued branching of the thread. Fruit. After a while (usually two or three days’ growth) the surface of the mold begins to show some color, — either blue, brown, red, or some other color. The appear- ance of the color on the surface indicates that the plant is fruiting, i.e. producing spores or reproductive bodies. The spores of different species of mold are produced in quite different ways, and botanists classify molds by their methods of forming fruit. It will not be necessary for us to consider more than one or two of them. In the common blue mold the spores are produced as follows. After the mycelium has grown for some time there arise from its surface tiny threads growing vertically into the air. These threads, after extending for a very short distance, divide into little branches (as shown in Fig. 5, c), several branches arising from a single stem. After these branches have grown for a short distance they begin to be divided by slight constrictions, like rings, around them, so that each one of them looks like a string of beads (Fig. 5, ¢). These rings cut deeper and deeper into the branch until finally it is broken up into a string of a dozen or more small round balls (Fig. 6). These little balls (Fig. 6) are the spores. When seen under the microscope they appear quite transparent, but when a 18 BACTERIA, YEASTS, AND MOLDS considerable number of them are seen together they have a bluish tinge. The spore-bearing branches spring up in thousands all over the mold, and after a few days its sur- face is covered with a mass of thousands of spores, giving to the mold first a slightly blue color and later a darker ie blue, until the entire sur- face finally becomes cov- ered with the well-known shade spoken of as blue mold. These spores are ex- tremely light, are very easily blown by the winds and readi- ly float inthe air. Every breath of air striking a Fic. 7. A colony of Mucor, showing the. mycelium and the sporangium of the fruit capsules. Ata is a large sporangium filled with spores. mass of molds in full fruit will detach some of these minute spores and blow them away. The species of different molds can easily be distinguished by their different modes of forming spores. A mold com- mon on fruit and bread, called Mucor (Fig. 2), produces its spores inside of little sacs borne on long stalks. The mycelium in this mold is coarse and the threads are easily visible, making a loose mass of delicate fibers, and some- times forming upon bread a fluffy growth an inch thick (Fig. 2). When ready to fruit, threads grow vertically into the air and the end of each thread soon swells into a small rounded knob. This knob continues to grow until FRUITING OF MOLDS 19 it becomes a ball of considerable size, at first white, but finally black, and large enough to be seen with the naked eye (Fig. 7). Inside of this ball the living substance of the plant soon breaks up into hundreds of minute bodies (Fig. 7). These are the spores, and after they have become formed the sacs which hold them (sporangia) burst and the little spores are thrown out to be blown about by the wind. These molds are at first soft and white, but later blackfrom the ‘abundance of these spore sacs. Another very common sort of mold fruits still differently (As- pergillus) A fine, threadlike Fic.8. A colony of Aspergillus, showing mycelium and spore clusters. The lower figures show in detail the method of spore formation. mycelium is produced, as in. . the other cases, and from it grow the fruiting branches. At the end of each fruiting branch grows a little round ball, from all> sides of which project many little knobs (Fig. 8, a). These knobs lengthen a little, but soon break up into round spores very much like the branches of blue mold (Fig. 8, a'-c). The result is that, since they pro- trude in all directions, there appears on the end of each fruiting branch a little rounded mass, looking very much 20 BACTERIA, YEASTS, AND MOLDS like a corn ball (Fig. 8, 2), —a resemblance which is very striking in some species when the spores are white. This species of mold, even after producing its fruit, remains white; but a careful examination shows it to be covered all over with minute white balls just big enough to be seen by the naked eye, but looking very beautiful under the microscope (Fig. 9). Each ball is a mass of scores of spores. Some molds of this last type produce brown spores in- stead of white. Of the scores of species of molds each has its own method of produ- cing spores. Each is at first a white, threadlike myce- lium, but each in Fic. 9. A colony of Aspergillus as shown under the microscope on a black background. : time shows spots of color. When the color begins to appear it commonly means that the mold is producing spores. The spores are nearly always so small and light as to be blown easily by the wind, and in this way they are carried to and fro. The air in any household is almost sure to be filled with them in greater or less abundance, as can easily be proved by simple experiment. Figs. 14-17 showa variety of com- mon molds, with their methods of forming spores. FRUITING OF MOLDS 21 a a qg 2 fs vet | Dc es Fic. 10. Mucor,a Fic. 11. Antenaria, a com- common mold. mon mold found upon apples. Mycelium shown.at a, and en- larged fruiting bodies at 4. SSsgs— ae oa Fic. 12. Fruiting bodies of another Fic. 13. Fruiting bodies species of Anjfenaria. of a mold found upon apple scab, Cephalo- thectum. Fic. 14. Stysanus, a common mold. «, mycelium; 4, fruiting branch. Fic. 15. A common household mold. 22 BACTERIA, YEASTS, AND MOLDS Germination of Spores. The function of these spores is to reproduce the plant. If one of them lights upon a proper material having sufficient warmth, moisture, and nourishment for its life, it soon germinates and sends out from itself a little thread (Fig. 5, a). This thread feeds upon the material on which it is growing, and continues to extend and branch until within a few hours a new mycelium is produced, thrusting its way into O- Spores Cog 9 id Fics. 16 and 17. Two species of molds, A/ozilia; common in cheese. the food substance and developing into a typical mold. After a day or two the spores are again produced (Fig. 5), and the process is repeated. The air is almost always so well filled with spores of molds that it is quite impossible to leave any food product exposed for any length of time without a number of these living spores falling upon it. If a piece of moist bread, for example, is exposed to the air for an hour or’so in an ordinary room, and is then cov- ered with a bell glass in such a way as to keep it moist, it will, in the course of a day or two, become covered with molds which have come from the sprouting of spores that FRUITING OF MOLDS PLaTE I PLATE IT Fic. 18. Plates exposed to the air before and after sweeping, showing the abundance of mold spores in the air. The upper plate was exposed before sweeping, and contains one mold; the lower after sweeping, and contains numerous molds. Each was exposed for one minute. 24 BACTERIA, YEASTS, AND MOLDS fall upon it. These spores— including species already described, as well as a variety of others — are almost sure to be floating in the air, and one of the valuable practical lessons for the housewife to learn is that the ordinary air of her house is filled with mold spores which are sure to get upon any food material that is left exposed. The mold spores, although very light, are slightly heavier than the air, and after floating awhile they sink to the floor, if the air is quiet, where they remain until the air is again disturbed. Sweeping stirs them up, and so does dusting. Fig. 18 represents two plates filled with a jelly upon which molds will readily grow. Plate I was opened to the air for one minute in an ordinary room and then closed. The room was then swept and Plate II was exposed to the air for the same length of time. Both were then set aside until the spores germinated, when the photographs were made. The plate exposed to ordinary air shows only one mold, while that exposed after the room was swept contained large numbers. Dusting a room pro- duces similar results. Even walking through a room, espe- cially with long dresses that sweep the floor, will stir up mold spores. The practical conclusions are thus taught that wiping up dust with a damp cloth is far better than dusting ; that carpet sweepers are better than brooms; and lastly, that no food should be exposed to the air of a recently swept room. PROTECTION OF Foop FRom Mo.Lps The fact that the molding of food starts from spores that drop upon it from the air suggests protecting the food by the simple means of keeping the spores away from PROTECTION OF FOOD 25 it. If we can keep the spores away, no trouble of this sort will arise. For example, jellies made from the juice of fruit, which the housewife puts up for winter use, are excellent material for mold growth, as many a person has discovered after the jellies have been stored away for a time. There is, however, little difficulty in preventing the molding. In making the jelly the material is commonly heated sufficiently to kill the spores present, and if it is afterwards properly covered it will keep well enough. After the jelly has been poured into the jelly tumblers and has become somewhat hardened, the surface should be moistened with some alcoholic solution, like brandy, or even pure alcohol. Then a piece of clean white paper the size of the tumbler should be placed upon the surface of the jelly. After this the tumbler should be covered with a piece of paper tightly glued over its edges; or tumblers with special covers may be used instead of ordinary tum- blers covered with paper. The alcohol aids in destroying the spores that may have chanced to light on the surface of the jelly, and the paper, if properly fastened, will pre- vent the entrance of more. This device is not sufficient to exclude dacterza, and if the jelly were liable to decay, the simple paper covers would not protect it from bac- terial action. But the method is sufficient to prevent the growth of molds in a majority of cases. Molds fre- quently grow upon the top of the papers in such jelly tumblers, but they do no hurt to the contents below. Other devices for closing the tumblers are also used. Sometimes a little white of an egg is used instead of alco- hol. Instead of using paper, a little melted paraffin may be poured upon the surface of the jelly, thus sealing it 26 BACTERIA, YEASTS, AND MOLDS effectually. The paraffin should be melted in some dish, like a cup, at the lowest temperature at which it will melt, about 140°. The surface of the jelly may then be covered with a thin layer, which will quickly harden. These methods of protecting jelly are not sure, and even after sealing it is necessary to keep the jelly in a dry place to insure its keeping properly. Spores may be left under the paraffin, and it is difficult or impossible to seal so that no mold spore can subsequently enter, Jel- lies should therefore be stored in dzy closets to keep them from spoiling. If it should happen that no dry closet is convenient, the air in a damp closet may be partly dried by keeping unslaked lime in bowls on shelves near the jelly. These will absorb the moisture and aid in checking the molding. The lime should be renewed from time to time. Canned goods will also sometimes mold when the process of canning has not been thorough. This will however be considered later. We must notice here, how- ever, that when cans of fruit are opened and exposed to the air, mold spores are very likely to drop into them, and if they are then shut up again the contents of the can are almost sure to show a fine crop of molds in a few days. It is almost impossible to open a can of fruit, take out a part of it, and close again, without allowing mold spores to drop into it from the air. This must, of course, be guarded against, and if the whole contents of the can can- not be used at once, the part that remains should be boiled and once more closed, as in the original canning. By such heating the spores that may have dropped in while the can was opened are destroyed, and it may be closed and set away safely. MATERIAL LIABLE TO MOLD 27 MATERIAL WHICH IS LIABLE TO MoLp Since molds are fungi, they require to be fed with organic food. Hence they are unable to live, as green plants can, in purely mineral soil. Indeed, they do not grow readily anywhere except upon rich food, and they grow best when feeding upon the same kind of foods that animals require. Whatever contains organic material will support them. They feed readily upon bread, cheese, or meat, and they can also support themselves upon leather or upon woolen or cotton cloth. Some molds grow easily upon damp wood; but although thus capable of living upon almost anything except mineral matter, they grow much more readily on some materials than on others. Of common foods, cheese is probably the one that molds most readily, partly because it is always more or less moist, and partly because it is quite sure to be inoc- ulated with mold spores. Wheat flour, or any material made from it, like bread or cake, is sure to mold if kept sufficiently moist and warm. The molding of the flour in the flour barrel is occasionally noticed, and the molding of bread is a common occurrence. All other forms of flour and meal, as well as articles made from them, mold readily enough. Even pickles will occasionally mold; for the intense acid of the vinegar, while it quite prevents the action of the common putrefactive organisms, does not necessarily stop the growth of molds. In short, almost any of the foods which are found in the pantry may, under certain conditions, show mold growth upon their surfaces. Molding is not confined to food in the pantry, for other substances which contain organic material can furnish 28 BACTERIA, YEASTS, AND MOLDS proper sustenance for mold growth. Leather, like that of old shoes, if kept in a warm, moist atmosphere, becomes covered with mildew. The same is true of carpets and of woolen or cotton cloth. Such material does not furnish a very luxuriant growth, the effect being commonly called mildew instead of molding. At first sight there seems little similarity between molding and mildew, but the microscope tells us that mildew is really nothing more than the growth of certain species of molds that have not developed very luxuriantly. Paper is also liable to mold if kept damp, and certain molds are occasionally found in and upon books. Even woodwork will sometimes mold, especially in dark, damp. cellars. In short, almost anything in the household which is of vegetable or animal nature may, under proper circum- stances, furnish a substratum which can develop a more or less luxuriant crop of these plants. Resutts oF Moitp GrowtTH The effect of mold growth varies with the species of the mold and also with the material on which it is grow- ing. Sometimes molds are useful, as for example in the ripening of Roquefort cheeses. Upon most of our food products, however, their action is injurious in at least four directions. (1) They make the food unsightly, for few people would be willing to use as food any material upon which a luxuriant growth has made its appearance. (2) They generally injure the taste of the foods, for a peculiar flavor is sure to be imparted to any food product where mold has grown, and after the mold has a luxuriant growth the flavor of the food is so modified that we are RESULTS OF MOLD GROWTH 20 usually not willing to eat it. (3) They affect the odor of food. Mold is always sure in time to develop a peculiar smell which we generally speak of as “musty.” Musti- ness, indeed, is commonly nothing more than the odor that comes from molds. It is due in part to the presence of the microscopic spores which arise from the mold mass, and which, breathed into the nostrils, produce the pecul- iar effect upon the nose which gives rise to the odor. It is due also in part to gases which arise from the molding material as the result of deccmposition. At all events, mustiness is always character- istic of mold growth, and whenever any material or any room smells musty we may be confident that it contains growing molds. We may be sure also that any material capable of molding, if left in such a musty room, will be sure to show signs of molding in a short time. (4) In the end the growth of the molds results in the total ruin of the food, since after a while mold growth produces decomposition, putrefaction, and decay. These later changes are due to the fact that the molds are consuming the material as their own food. While they use the food for their own purposes they are producing chemical changes which result in the production Fic. 19. A bit of Stilton cheese. The dark parts are masses of mold spores. 30 BACTERIA, YEASTS, AND MOLDS of the peculiarly flavored products characteristic of certain forms of decay, rot, or putrefaction. It must not be understood, however, that putrefaction is produced wholly by the action of molds, even in the materials on which molds are visibly growing ; for another class of organisms to be considered later, the bacteria, is more commonly concerned in putrefaction. But molds contribute largely to the development of putrefaction, and in the case of some materials, as fruits, molds are prac- tically the sole cause of this phenomenon. MoLps UPON FooD NOT NECESSARILY UNWHOLESOME The result of these various changes is that almost all foods are soon spoiled if molds are allowed to grow upon them for any considerable time. They rapidly change in flavor, odor, and in ap- pearance, and eventually the putrefaction or decay makes them utterly value- less. If, however, the molding is checked quickly andthe food preserved from Fic. 20. A bit of Gorgonzola further molding, or if it is cheese. consumed at once, there is no reason why the food should not’be utilized, for the mold itself is not particularly unwholesome. We may consume food that has begun to mold without its produ- cing any ill effects upon us, provided that the molding has not extended too far and that we do not eat a great quantity USEFUL MOLDS 31 of it. Indeed, Stilton (Fig. 19), Gorgonzola (Fig. 20), and Roquefort cheeses owe their delicious flavors to molds. If a large quantity of moldy material is taken at once, it is possible that a slight poisonous effect may be produced; but this practically’never occurs in the consumption of moldy food. It is well to remember, therefore, that molds are not unhealthful. It is not always necessary to throw away moldy food; much of it may be used. Moldy cheese is by no means ruined, for the moldy surface may be scraped off and the center will be found as good as ever. Many samples of preserves or jellies which are beginning to mold may be utilized if we simply stop the growth of the mold and preserve the food from further molding. It may be that the mold has developed a slight musty odor and taste, which would, perhaps, injure the value of the food from the standpoint of the palate, but they will not have injured its ease of digestion or its value as a food. It is, however, the desire of the housewife to prevent molding so far as possible, and to check it quickly if it begins, in order that she may thus preserve the valuable foods. To understand the methods by which we may best prevent the growth of mold, or check it if it once begins, we must next consider the conditions most favorable for mold growth. CHAPTER III CONDITIONS FAVORING MOLD GROWTH ‘Moisture. The factor of primary importance is water. A vigorous growth of molds needs an abundance of mois- ture, and in dry material they will not grow at all. This moisture may be supplied by the air in which the food is kept, or by the food itself. 1. Many materials which do not contain in themselves enough water to support the development of molds will serve as a fine locality for mold growth, provided they are kept in a sufficiently damp atmosphere. If the air of a room becomes damp or “close,” as we say, it is almost certain that molds will begin to grow upon any organic substance. Thus a large variety of materials in the house- hold, ordinarily free from molding, may show signs of mildew during a damp season. The mustiness of a closed room is due to the presence of molds and is always an indication of dampness, for dry rooms neither show signs of mold nor do they smell musty. 2. Some materials contain within themselves sufficient water to produce a vigorous development of molds quite independent of the moisture present in the air. Fruits, for example, are so full of water that it makes little differ- ence to them whether the atmosphere in which they are kept is dry or saturated with moisture. Jf the mold once gets a start, the fruit itself furnishes all necessary water. 32 EFFECT OF MOISTURE 33. The same might be true of other very moist food materials. But while a majority of food stuffs are liable to mold in our houses, they are commonly not moist enough to sup- port mold growth if kept in a moderately dry atmosphere ; and even in the case of fruit a moist atmosphere is neces- sary to start the growth. From these facts it follows that food capable of being thoroughly dried may be protected absolutely and per- manently from molding. Various kinds of flour and meal, although furnishing excellent food for molds, will keep indefinitely while dry. This statement is an absolute one with no exception. It must, however, be remembered that even the driest of foods may become moist in a damp atmosphere, and that hence the driest material, if exposed to a moist atmosphere, may in a short time show the growth of molds. Flour in a flour barrel, dried apples packed in a box, and dried meat hung in a shed may all show signs of mold in damp seasons. Molds will start upon carpets in damp weather, and upon leather boots or shoes if they are kept in damp closets sufficiently long for the germination of the mold spores that are floating in the air. Books in our libraries and clothes stored away in closets or drawers are not free from molding in damp weather. Sometimes leather pocketbooks will develop mold in our pockets, stimulated by the moisture and heat in our bodies, and will become covered with the well-known mil- dew. Boxes of cotton cloth shipped for transport may mold on their journey if the weather is moist. In short, in damp weather no animal nor vegetable material is free from the possibility of molding, and dryness is in all cases an efficient remedy. 34 BACTERIA, YEASTS, AND MOLDS It is evident that drying may be conveniently used for preserving cloth, leather, etc. Thorough airing and drying by exposure to sunlight, followed by brushing, is the cure for mildew. It is also well to remember that soiled clothes mold much more readily than clean clothes, probably because the dirt upon the cloth furnishes a little food for the molds which suits them better than the cloth itself. Soiled clothing, if packed away. and left undisturbed for a time, is quite likely to be injured by molding. While moisture is necessary for mold growth, it is true, on the other hand, that too much moisture is generally not favorable to molds. Very wet foods, like fresh meat, milk, etc., do not commonly mold, although they readily decay from the action of bacteria. Stagnation of the Air. Molds grow better in an atmos- phere where the air is not freely moving, and therefore are much more vigorous in foods shut up in tight boxes than in the same foods when currents of air are allowed to flow over them. The reason for this is not wholly known. It may be that the agitation of the thread pro- duced by the currents of air is injurious to the growth of molds ; but it is more probable that the air currents simply tend to evaporate the moisture from the surface too rapidly to allow the growth of molds. Certain it is that a vigor- ous growth of mold, upon a bit of cheese for example, will, when exposed to the air, change from a fine, loose, fluffy mass to a dense, flat, matted layer, and will soon almost cease to grow. Whether this is due to evapora- tion of moisture or to some other cause is a matter of no great practical importance in the house. The facé is borne out by long experience, that molds grow in closed vessels EFFECT OF AIR ON MOLD GROWTH 35 much more rapidly than upon open surfaces. As a result we find that molding is more likely to take place in food when a number of pieces are piled together in a heap, as, for instance, several slices of bread or a number of pieces of fruit. Such a heap furnishes many little recesses partly surrounded by walls which prevent the free pas- sage of air currents, and these little nooks furnish a sheltered place for the mold spores to germinate. If bits of bread are spread out on the shelf of a damp closet they will probably not mold at all, while the same pieces would mold if piled in a heap. Foods with smooth surfaces are, for the same reason, not so liable to mold as those filled with little cavities, like bread. On the other hand, molds require some air, and molding almost always begins on the surface. Although, as we have seen, the mold thread can force its way down into the solid substance of food, it always starts upon some sur- face exposed to the air. To grow vigorously, the threads demand an abundance of air, and, as a consequence, will never grow in the center of solid food masses, or at least, if they do, they grow there very slowly. After starting on the surface they may grow for some distance into solid food substance. In the manufacture of Roquefort cheese it is desired that molds should start at the center of a hard cheese mass. To bring this about the growth is stimu- lated by piercing the cheeses full of holes by means of long needles, so that air can penetrate to the center. Airis quite necessary for the formation of the spores, and the fruiting of the mold practically always occurs upon the free surfaces. We need not expect any molding in the center of a mass of food unless some signs of it are visible externally. 36 BACTERIA, YEASTS, AND MOLDS Darkness. Molds will grow both in light and darkness, but on the whole they grow somewhat better in darkness than in light. Indeed, the action of direct sunlight is injurious to them, and most species of molds fail to grow upon the surfaces of material exposed to sunlight. Asa result of this we rarely find molds growing upon the free surfaces of materials exposed to the sunlight or even to bright light. This is not universally true, but it is the common experience of housewives to find that materials, when shut up in dark closets, are very much more liable to mold than when left in a light room. This is doubtless due, in part, to the fact that exposure to sunlight, or even to the air of a light room, evaporates moisture rapidly and thus checks molding. But it is not wholly due to this, for light itself appears to be deleterious to mold growth. Temperature. Molds require a moderately warm tem- perature for vigorous growth. At a temperature slightly below freezing they will not grow at all, and at a few degrees above freezing their growth is very slight. Some species of molds, however, grow readily enough at 40°, growing better at this than at a warmer temperature. Hence it follows that the temperature of an ice chest will not wholly prevent molding. Most common molds, how- ever, either fail to grow at an ice-chest temperature or grow very slowly. As the temperature increases, how- ever, the growth becomes more vigorous, and at tem- peratures varying from 70° to 100° the growth of these plants is stimulated to their highest activity. A practical result from these facts is that any material which can be kept sufficiently cool will fail to show signs of mold, even EFFECT OF TEMPERATURE 37 though tightly closed in an atmosphere saturated with, moisture and abundantly sown with mold spores. Even in cold-storage houses, where the temperature is below freez- ing, there may be a slight molding, but if the temperature is near freezing, molding is almost prevented. The ice chest also, though much warmer, very decidedly checks the tendency in most foods to mold. Cheese, for example, after being cut, should be kept in a closed dish, to prevent its drying too rapidly ; but it molds rapidly when thus covered. If the dish be placed in an ordinary refrigerator, the contents will keep a long time. Killing by Heat. In considering the relation of tem- perature to molds a fact of great importance is that high heat will always destroy molds and their spores. A tem- perature considerably below boiling, 150° or 160°, is quite sufficient to destroy the mycelium of the molds, although the spores may resist this temperature ; but a temperature of boiling is necessary to kill the spores. Hence any food which has begun to mold, and which is of a character to allow heating, may be protected from the further growth of the mold by boiling. A temperature considerably below boiling will check mold growth, though not actually kill- ing the spores. This method of treatment will be possible for many preserves, canned foods, or any food that has been previously cooked. It may be applied to preserves, sauces, jellies, mince-meat, and even pickles. It would not be practicable, however, with foods whose flavor is destroyed by cooking. Fresh fruit which has begun to mold cannot be treated in this way without destroying the original fruit flavor and giving in its place the taste of fruit preserves or sauce. It is always necessary to 38 BACTERIA, YEASTS, AND MOLDS remember that after such heating the food is liable again to receive more mold spores from the air and may there- fore later show another growth of molds. Reaction. By reaction is meant the condition of food as to its acidity. Some foods are acid (lemons, pickles), while many may have the opposite reaction, called alkaline. The reaction of food is a matter of considerable impor- tance in determining its likelihood to mold. It is true that both alkaline and acid foods may mold, but in general acid foods mold more readily. Lemons are very acid, and so are ordinary fruits, all of which mold very quickly. Molds may even grow upon such strong acid materials as pickles. Bacteria, the second great agent in producing decay, grow in alkaline but not commonly in acid foods. Hence it fol- lows that materials which are most liable to mold are not likely to support the growth of bacteria, and vice versa. PRACTICAL SUMMARY From these general observations it will be seen that molds will grow best in dark, damp rooms or in corners of the rooms where there is not free circulation of air; they will flourish in heaps of food where many pieces are massed together; they will grow vigorously upon food inclosed in jars or boxes, and they prefer darkness rather than light. From all these facts we may reach practical sugges- tions as to the methods of avoiding the growth of molds. (1) The most important of all is that food should, so far as possible, be kept tolerably dry. If it is of a nature that will stand drying, it may be protected indefinitely if once PREVENTING MOLD GROWTH 39 dried and not allowed subsequently to become damp. Indeed, in a pantry or a cellar, molding commonly means excessive dampness. (2) Foods are more free from mold if exposed as much as practicable to light rather than if kept stored in dark boxes. It is of course necessary to keep some kinds of food in closed boxes in order to pre- vent them from becoming too dry, but it is useful to expose -such food occasionally to the air and sunlight in order to check the development of molds that otherwise might grow. (3) The growth of molds may be almost com- pletely stopped by lowering the temperature, and there- fore foods that are particularly liable to mold may be prevented from molding for a long time if kept in an ice chest. The temperature of an ice chest is not low enough to prevent all mold growth, but it is so low that some species of molds do not grow at all, while others grow so very slowly that even a material like cheese, which is quite sure to mold if shut up in the dark at ordinary temperatures, may be preserved in a dark ice chest for many days or even weeks without molding suffi- ciently to do it injury, CHAPTER IV THE DECAY OF FRUIT; USEFUL MOLDS; MOLD DISEASES Of all food materials commonly found in the house- hold none are so much injured by molds as fruits. Fic. 21. An apple beginning to decay under the action of certain species of molds. Most pears, plums, and peaches decay rapidly; apples, oranges, and bananas keep somewhat =| longer, but it is a } universal experience that none of our ordinary fruits can be kept for any con- siderable length of time without de- caying (Fig. 21). Winter apples, with their solid flesh and their tough, smooth skin, can be kept for many months without rotting, and the thick skins of oranges and lemons protect thema longtime. But thin-skinned fruits, like cher- ries or berries, can be kept only a comparatively few days. The decay of fruit is by no means always alike, and it is produced by a variety of causes. If one simply examines 40 THE DECAY OF FRUIT 4l decaying apples, pears, lemons, and bananas, the differ- ence in the character of the decay is quite evident both to the eye and to the smell. Bztter rot, black rot, and brown vot are three types produced by three different organisms. It is not within the scope of our study to describe the different kinds of decay which appear in com- mon fruit. The causes may be numerous, but in the majority of the examples of decayed fruit the active agency, Fic. 22. Monilia, a common species of mold causing fruit decay. at the start at least, is the growth of molds. In later stages of the decay bacteria may be concerned, but it is always molds that begin the process. There are a num- ber of species of molds intimately associated with the decay of fruits. The common blue mold (Fig. 7) is one of the most widely distributed, but there are several others (Figs. 22, 23, 24). METHOD OF INFECTION AND DISTRIBUTION To understand the decay of fruit we must first bear in mind that mold spores are constantly floating in the air, and that they may also be carried easily upon the feet of insects that chance to light upon a bit of spore-bearing mold. By some such agency mold spores are quite sure 42 BACTERIA, YEASTS, AND MOLDS to find their way to the skin of any piece of fruit. But after they fall upon the fruit they will not grow unless the conditions are right. If the skin is whole and smooth and dry, they do not readily germinate. Commonly they start at some small crack in the skin through which the thread sprouting from the spore can thrust itself into the softer parts within. Hence whole-skinned fruits are easier to keep than those with bruises. If the spores findsufficient moisture on the skin, and a convenient crack, they soon send a tiny myce- lium thread into the fruit. This grows luxuriantly, branching profusely, and presently pushes its way in every direction through the soft pulp of the fruit. The fruit begins to soften and eer eat ee decay. The rotting is caused Fe. 23, Mons shonin SIC" by the growth of the mod sprouting of spores at @ and 4. mycelium in the flesh, the visible decaying spots being simply the external evidence of the mold growing within. After a time the mold begins to form its spores. To do this it generally breaks through the skin so that the spores may be formed in the air. These spores can easily be seen in a well-decayed apple (Fig. 25). The spores thus produced are then scattered into the air from the broken skin of the fruit, They are carried either by air DISTRIBUTION OF SPORES 43 currents or by insects, or, if the pieces of fruit are in direct contact with each other, as is almost always the case when packed, one piece of fruit will directly infect the next and thus start a new center of decay. In this way decay which begins with a single piece of fruit is Fic. 24. Another species of Afonz/ia taken from a decaying apple, showing formation of spores. sure in a short space of time to extend to the neighbor- ing pieces. From a single decaying apple, infection may spread from apple to apple until a whole barrel speedily becomes decayed and ruined. It is an example of direct contagion. A practical suggestion arising from these facts is the wisdom of removing from the vicinity of sound fruits all 44 BACTERIA, YEASTS, AND MOLDS that show signs of decay, since decaying fruit will surely be shedding spores which will infect the sound fruit. Such fruit, therefore, should not be allowed to remain in a pantry with other fruit, nor in a cellar. Nor should it be allowed to accumulate in heaps near the home, for insects and air currents are sure to distribute the spores. The removal of all decaying fruit, or its total destruction, therefore, is a necessary safeguard to protect the sound fruit that remains. PROTECTION OF FRUIT FROM DECAY There is no thoroughly successful remedy for the decay of fruit. It is true that fruit may be preserved absolutely from such de- cay; but this can only be done by the process of canning, or by some other method of preserv- ing which involves oper- ations totally changing thecharacterof thefruit. These we shall consider inalater chapter. It is not possible by any Fic. 25. A small bit of an apple under a microscope, showing the molds breaking known means topreserve through the skin to produce spores, and showing the mycelium running through the substance of the apple. fruit indefinitely from the attack of molds and at the same time to re- tain its original, natural, fresh condition. Even the hardiest and toughest of fruits will, in the course of months, begin to PROTECTING FRUITS FROM DECAY 45 show signs of decay, though some kinds may be preserved much longer than others. But although it is not possible to prevent absolutely the growth of molds, it is quite pos- sible to delay it very materially if proper care is taken of the fruit. Fruit which would ordinarily keep only a few weeks may, if properly treated, be kept through the winter until the spring. Different fruits vary much in their ease of preservation. Peaches, cherries, and berries can hardly be preserved at all; pears only a little longer. Grapes can be kept a few weeks or longer if special care is taken. Apples, oranges, and lemons can be kept many weeks or even months. Moisture. We have seen that plenty of moisture is a necessary condition of mold growth. But in considering the application of this fact to the decaying of fruit we must remember that the interior of fresh fruit itself is always moist, containing, indeed, quite sufficient water for the development of the molds, provided they can once get through the skin. Hence the decay of fruit goes on about equally well in moist and in dry air, provided the molds once get a start, and it cannot be prevented by keep- ing the fruit dry. ; But the moisture which accumulates upon the skin of the fruit is a most important factor in its tendency to decay. The mold spores are quite incapable of germinat- ing unless they are moistened, and any fruit, the skin of which is kept perfectly dry, is very largely protected from decay, because the spores get no opportunity for germinating. If the skin of the fruit can be kept clean as well as dry, the rotting may be delayed for a very long time. 46 BACTERIA, YEASTS, AND MOLDS . This is no easy matter, for there are almost sure to be some depressions in the skin, such as cracks or dents, and in these moisture is sure to accumulate. The depressions around the stem or the eye of an apple serve the same . end, and, in damp air, water is so likely to accumulate here.that molding starts readily. Once germinated the threads quickly force their way into the apple around the stem and find plenty of moisture in the flesh of the fruit, Hence any devices which tend to keep the skin of the fruit dry are at the same time devices for checking the first steps of decay. Fruit whose skin is wiped frequently with a dry cloth will keep better than fruit that is not thus wiped. This question of moisture explains also why it is that fruits begin to decay first at points where two pieces come in contact with each other, since here there is a much better opportunity for moisture to con- dense. We also learn why fruit which has been cooled to a very low temperature—as in cold storage — and subsequently warmed, may decay more quickly than fruit which has not been cooled. The cold skin of the fruit taken from cold storage causes a slight condensation of water, and then when subsequently warmed this water furnishes a favorable starting point for the germination of mold spores. This explains also why covering with sawdust or charcoal is of great value in checking the decay of fruit. If packed in sawdust, fruit may be pre- served a long time, because the sawdust absorbs moisture and prevents the accumulation of water upon the fruit skin. Charcoal serves the same purpose. For some fruits, like pears, oat chaff or rye chaff serves better than sawdust. VALUE OF CLEAN SKIN 47 This absorption of moisture explains also the efficacy of one of the best means known for preventing the decay of fruits. Experience of recent years has shown that the wrapping of fruits with paper is a more efficient means of protecting them from the ordinary rot than almost any device that has ever been adopted. There may be two reasons for this. Wrapping the fruit with paper protects it to a considerable extent from mold spores, which would drop upon the skin from the air if it were not thus pro- tected. But this is doubtless not the chief reason for the value of the paper wrapper, since the fruit is almost sure to be infected with the mold spores while still on the trees, and certainly before it can be wrapped in the paper. The paper used is of a soft, porous nature, and, when prop- erly wrapped around the fruit, absorbs quickly any mois- ture that may be upon the skin, and prevents moisture from further condensation. Clean Skin. The facts mentioned also clearly explain the value of a smooth skin. Since decay always starts from spores that lodge on the skin, any method of pre- venting their lodging or of removing them will protect the fruit; hence the wiping of fruit with a clean cloth will be useful in protecting it from decay. Wiping can- not, indeed, wholly remove the spores, but it aids materi- ally. Moreover, if the wiping is done with a dry cloth, it will also remove the moisture, a matter of no small impor- tance. Fruit dealers, who have learned by experience how to handle fruit, understand well that a frequentywiping of fruit till it is dry and clean is a necessity for its best preservation. It is sometimes surprising to see in what fine condition some dealers can keep fruit far into the 9 48 BACTERIA, YEASTS, AND MOLDS spring months by the simple devices of low temperature and clean, dry skins. Temperature. We have already noticed how effectively low temperatures check the growth of molds, and this applies of course to their growth in fruit as well as else- where. If fruits could be actually frozen, the decay could be indefinitely prevented. But this is not possible with common fruit, since the freezing injures its character. All that can be done, therefore, is to cool the fruit to as near the freezing point as possible without actually freezing it. If the temperature is lowered until the fruit is near to the freezing point, the growth of the molds may be so delayed as effectually to prevent the fruit from decaying for very many months. This can be done readily in the modern cold-storage plant, and in the last few years fruit growers have been learning that cold storage furnishes a means of keeping fruit for the spring market. To be sure the expense of such storage is a considerable item, but the extra price that may be received in the spring may more than make it good. If one has not the opportunity for cold storage, it is best to keep fruit in cool cellars where the temperature does not go down to freezing and is toler- ably constant. The lower the temperature (above freez- ing) the better. The temperatures of cool cellars are not, however, low enough to prevent mold growth wholly. They will not prevent the final decay of the fruit, but they are very useful in delaying it. When fruits are removed from such cellars it must be remembered that they are cold and will condense water rapidly on their surfaces. They should be wiped dry after being in the warm air a few hours, or they will decay quickly. DECAY DUE TO DISEASE 49 RottTine oF FRUIT DUE TO DISEASES OF THE Fruit TREE In addition to the rotting of fruit due to the growth of common molds, it is important to know that many diseases are caused by certain microdrganisms that attack the plants upon which they are growing, or attack the fruits themselves while still growing upon the fruit trees. These sometimes produce various kinds of rots and decay in the fruit even before it is plucked (Fig. 26,27). In some cases the fruit may appear to be perfectly sound when picked from the tree, but it is really already in- fected with molds which cause it later to show signs of decay (Fig. 21). Nearly all of the diseases in question are caused by molds somewhat similar to those we have already con- sidered, but of different species. Botanists know a large number Fic. 26. Peaches tumed into a hard mass (mummified) by the action of fungi. of species of molds which grow upon different fruit trees, producing diseases of the tree and accompanied by decay of the fruit. So far as concerns affairs of the household these imperfections are quite beyond the reach of efficient remedies. If the fruit which we buy at the market and 50 BACTERIA, YEASTS, AND MOLDS bring to our houses is already infected with the molds in question, nothing that we can do will protect it from their subsequent growth and consequent decay. The only alleviating remedy is, as mentioned in other cases, to keep the fruit cool, because none of these microorganisms grow readily while in low temperatures. Dryness is of no value, since the molds are already within the fruit, where there is moisture enough. This cause of the de- cay of fruit is, however, of no very great signifi- cance to the ordinary household, because in a great majority of cases the fruits infested with these troubles will show some signs of decay be- fore they reach the mar- ket. The loss comes Fic. 27. Peaches decaying on the tree. UPON the fruit grower, upon the person whobuys the fruit for storing, or upon the dealer; rarely will the decay thus produced be delayed sufficiently for the fruit to be marketed, sold, and carried away bythe customers. The consumer would not distinguish this from the more com- mon types of decay. For this reason this species of fruit disease, while of great significance to the farmer and to the one who handles fruits, is of no very great impor- tance in the ordinary household and need not here be further considered. USEFUL MOLDS 51 Utitity oF Motps We never look upon molds as of any particular utility. Nevertheless, when we study their relations in nature we find that they are of the utmost importance. In the pro- cesses which are going on in nature the molds form a very important link, aiding in furnishing different kinds of liv- ing beings with food. The woody part of trees contains a large amount of material which cannot be used as food by either plants or animals. Were it not for some agent which brings this material into condition for subsequent use by plants and animals, the food material of the world would in time become stored away in the form of wood, and the world would materially suffer as the result. But the tree trunk does not remain a hard, solid mass very long after it has fallen to the ground. It slowly softens and decays, until eventually it assumes a condition in which it can again be used for food by various animals and plants. Insects, for example, feed upon the decaying wood until, in time, the tree trunk is all consumed. In this process a group of fungi similar to molds plays an important part, for it is a mold-like mycelium growing through the hard surface of the wood that begins the softening necessary to make its utilization possible. With this we are not particularly concerned, for the household is not usually concerned in the decay of wood. Wood in the household may occasionally decay, but it is sucha rare circumstance that the housewife pays little attention to it. Outside of their agency in producing the decay of woods, molds are of no great utility, so far as we know at the present time. A few of our food products are, however, 52 BACTERIA, YEASTS, AND MOLDS benefited by the development of molds. As already noticed, the peculiar flavor of certain cheeses is due to the growth of molds. Rogwefort cheese, by a special device of the manufacturer, is caused to mold. When cut open this cheese shows green spots extending through its sub- stance, and these little green masses are simply the spores of molds which have developed in the cheese during its ripening. Svzz/ton cheese, a variety made in England, and Gorgonzola are also ripened by molds. Camembert cheese, a type of soft cheese very popular in Europe and begin- ning to obtain a considerable market in the United States, is always covered with molds which have developed dur- ing the ripening of the cheese, and have contributed to its flavor. rte cheese is another type whose flavors are due to molds, and there are several others less well known. DISEASES OF ANIMALS PRODUCED BY MoLps Some species of molds may live a parasitic life. Many species live as parasites upon plants, sending their myce- lium into the leaves or stems of the plants, and produ- cing thus a variety of diseases. With these we are not concerned in this work. A few molds can live a parasitic life upon animals, and there are consequently a few animal diseases produced by molds. The mold diseases of man- kind are confined to two or three common skin diseases, which sometimes become quite troublesome. The most common of these mold diseases in man is called ringworm, an affection of the skin which produces open sores. These sores spread in all directions from a central starting point, and as they spread they heal in MOLD DISEASES 53. the ceriter, though continuing to spread at the edge, thus producing a ringlike growth that has given origin to the Fic. 28. A mold (7richophyton) which produces ringworm. Ata is a bit of hair with the mold spores on the outside, and at da figure of the mold itself highly magnified. name. The affection is a troublesome one to heal, especially when it gets into the scalp; but it never pro- duces any very serious trouble. Two or three types of this disease have been found to be produced by two or three kinds of molds. Fig. 28 shows one of the common species that is the cause of ringworm. At a is shown a bit of hair with the mold fungus and mold spores growing upon it, and at 6 the fungus more highly Fic. 29.. Two pieces of hair from the scalp infested with a mold (Aficrospo- ron) producing ringworm. The upper figure shows the masses of spores attached to the outside of the hair; the lower figure shows the mold thread lying beneath the spores. magnified. Of the several species of molds that produce this trouble some are more liable to grow upon the hair 54 BACTERIA, YEASTS, AND MOLDS and others upon the smooth skin, the latter proving less troublesome to heal. A second skin disease is favus, some- times difficalt to distinguish from ringworm, although it is produced by a different species of mold, shown in Fig. 30, In the case of both of these diseases the affection is spread by means of mold spores discharged through the skin. They are liable to be carried from person to person by the use of combs or towels, or even cloths and sponges used in washing or bathing the skin. If, therefore, there is an example of ringworm in a family, it is imperative, in order to prevent the spread of the disease from one to Fic. 30. Amold (Achorion) pro. another, that the person suf- Gucing a second type of skin fering from the attack should disease Known as favus. At@ 1 ove his own combs, his own the mycelium is shown, at 4 the ? spores as found on hair. towels, his own sponges, and even his own soap for washing. By this means the disease can usually be confined to the person in whom it originally appears. The cure of such diseases must be left to a physician. MOoLpD-INFECTED Rooms Sometimes a room, like a pantry, may become badly infested with molds, so that all sorts of food become rapidly infected by them. This is an indication that the room is filled with mold spores in such numbers that they MOLD-INFECTED ROOMS oe a drop into everything exposed. The remedy for such con- dition is to get rid of the spores. The room should be vigorously swept and dusted, a windy day being chosen, and all windows and doors should be left wide open to blow out the dust. After a thorough airing the room should be closed again and left undisturbed until the remaining dust settles; then the floor, shelves, window sills, etc. should be wiped with a damp cloth. This will usually remove the spores, and food will subsequently be less liable to mold. A far better method is to use a vacuum cleaner, which removes the mold spores without scattering them in the air. SECTION II— YEASTS CHAPTER V YEASTS AND THEIR DISTRIBUTION FERMENTATION Yeasts are the natural agents which produce the phe- nomenon called fermentation. This term has several mean- ings to the scientists, but as the word is commonly used it refers to a process by which alcoholic liquors are pro- duced from sugary solutions. Fermentation is therefore the basis of the various popular beverages known to civilized as well as to uncivilized races. Fermentation is also the foundation of another phenomenon apparently quite different in its character ; for the raising of bread by yeast is just as truly a fermentation as is the manufacture of beer. The essential phenomena of fermentation are the destruction of sugar and the production from it of two other substances. The sugar is originally a solid, although it is very easily dissolved in water. It is a somewhat com- plex body, but by the action of yeasts it is easily broken to pieces to form two simpler ones. One of these, alcohol, is a liquid and remains in solution ; the other, carbon dioxide, is a gas and usually passes off from the solution in the form of bubbles (Fig. 31). It is this production of alcohol 56 FERMENTATION 57 and carbon dioxide that is the foundation of all fermenta- tive phenomena. place as follows. C,H,,0, = 2 C,H,O +2 CO, (sugar) (alcohol) (carbon dioxide) The phenomenon of alcoholic fer- mentation has been known for many centuries, traces of such knowledge being found as far back as we have any recorded history. Back in the earliest historical days mankind was familiar with certain fermented drinks. At the present time we find that the phenomena of fermentation are known by nearly all races of men, and there is hardly a tribe of savages without its own kind of fermented drink. These “stimulating” beverages are ob- tained frgm a variety of different materials by different races. The juice of grapes has long been used for the purpose, but various other fruits serve equally well. The juice of the palm tree is used by some races, and sweet juices of various other plants are also used. In all Chemists represent the action that takes é Fic. 31. Fermenting so- lution of molasses, showing at a the grow- ing yeast with the bub- bles of carbon dioxide arising, and also the arrangement for con- ducting the gas under- neath limewater at 4, for the purpose of de- termining the nature of the gas. cases the material must contain sugar, or something that can be converted into sugar; for it is always sugar which undergoes the fermentation, no other source of alcohol being practical for producing intoxicating beverages. In 58 BACTERIA, YEASTS, AND MOLDS the process of bread making, too, fermentation has been known almost as long; for we read in literature of leavened and unleavened bread at least three thousand years ago. Although fermentation was thus long known, its cause remained a mystery until the nineteenth century. The type of fermentation which we are considering is in all cases produced by essentially the same agency, a group of plants called yeasts. It is not always the same species of yeast, for the group includes quite a large number of different species. The commercial product is simply one kind that has been cultivated for commercial purposes; but there are many others in nature not under’ cultivation which may conveniently be called wild yeasts. All of the kinds are, however, very similar in appearance, have the same general characters, and are closely related to each other. Yeast was discovered about two centuries ago by a Dutch microscopist, who found fermented liquors filled with minute bodies, the significance of which he did not understand. Nor were they really appreciated until about the third decade of the nineteenth century. At that time it was quite conclusively demonstrated that these minute bodies were living organisms, capable of feeding, growing, and multiplying, and having a very close relation to the phenomena of fermentation. It was soon shown also that it was their gvow/hk that produced the fermentation, since this phenomenon would not occur unless these organisms were not only present but also growing and multiplying. In our study we must first learn the nature of the yeast plant. STRUCTURE OF YEASTS 59 WHAT ARE YEASTS Yeast plants are always microscopic, no species being large enough to be seen with the naked eye. When these tiny plants are massed together, as in a yeast cake, the mass may form a bulk large enough to be seen. We can see a yeast cake, ce but the individual yeast plant is not more than = of an inch in diameter, and this is far be- low the power of the unaided vision. By the microscope alone we learn that the yeast mass is made up of millions of minute bodies, Fic. 32. Common yeast very highly magnified. : : Figs. @ and 4 show vacuoles; ¢ shows a nucleus each of which is an z inside of the yeast cell; @ shows a budding individual yeast cell with the nucleus dividing; ¢ shows the cell divided, the new cell containing a bit of the plant. old nucleus. The yeast plants are much simpler than the molds. If a bit of a yeast cake be mixed with a little water and examined under the microscope, there will be found what is shown in Fig. 32. There will be seen large numbers: of minute oval bodies, sometimes very nearly spherical or sometimes considerably longer than broad. They are quite color- less and nearly transparent, as seen under the micro- scope, but whitish when seen in bulk. They have a 60 BACTERIA, YEASTS, AND MOLDS uniform, smooth outline, but inside of them may com- monly be seen some smaller bodies. There is usually ‘a somewhat rounded clear spot, as shown in Fig. 32, a, although in many cases instead of one we find two, three, or four smaller ones (Fig. 32, 6). These apparently rep- resent only little drops of an oily liquid and have, so far as we know, nothing very particular to do with the life of the yeast plant. These drops are called vacucles. No further bodies can be seen in the yeast cell by ordinary methods of study, although special microscopic devices show that there are other bodies inside (Fig. 32,¢). These other smaller bodies need not, however, concern us. The yeast cell thus described is quite unlike ordinary plants, showing less resemblance to them than molds. But though they bear no likeness to what we commonly call plants, biologists are unanimous in their opinion that they are to be classed with the molds as colorless plants and, hence, as fungi. Yeast exists in three somewhat different states: (1) the resting state; (2) the growing state; (3) the spore- bearing state. The yeast in an ordinary yeast cake already described is in the resting state. Such yeast appears as in Fig. 32, a, each plant being a single oval body or cell. It is alive but is not actively growing. The Growing State. When a little resting yeast is placed in a solution which contains proper material for food it begins at once to consume the food and grow. As it grows it multiplies by a method known as budding. Upon the sides of the yeast plants appear small buds (Fig. 33, a). Each bud at first appears as a little swelling on the side of the larger yeast cell. This little bud increases STRUCTURE OF YEASTS 61 in size until finally it may be as large as the original plant (Fig. 33, ¢). Usually by this time, if the growth is vigor- ous, there may have appeared a second bud. The latter sometimes arises from the side of the first cell and some- times from the side of the first bud, giving an appearance such as is shown at Fig. 33, ¢. This budding continues, the little buds appearing one after the other, until there are produced irregular-shaped groups like those shown at Fig. 33, @. For a considerable time the cells in these groups remain attached to each other, so that a little of the sediment from a fermenting liquid will appear under the microscope as shown in Fig. 33, d. After a while, how- ever, the different cells drop apart and may go into a resting stage, each cell remaining by itself. These cells are capable of growth and development, either imme- diately or subsequently, when again placed in a solution which furnishes them food. This method of multipli- cation, which is distinctly characteristic of yeasts and separates them sharply from bacteria, the next group of plants to be studied, is known as budding. The yeast. plants are therefore sometimes called the budding fungi. The Spore-bearing State. Under some conditions yeast plants produce a different kind of reproductive body known as spores. If a lot of yeast is placed where it has mois- ture but insufficient food, it does not grow by the normal Fic. 33. Growing yeast cells, showing method of budding and forming groups of cells. 62 BACTERIA, YEASTS, AND MOLDS method of budding, but its contents break up into several parts. In Fig. 34 is shown one of these yeast cells which has been growing on a porcelain plate without sufficient nourishment, and it will be seen that four small bodies have formed inside of the cell. These bodies are spores and are capable of Fic. 34. A yeast cell resisting for a long time a variety of i eels four adverse conditions, such as drying, heating, etc., without being injured. When the yeast cell breaks, the little spores burst forth ready to be distributed by the winds or by any other convenient means. Not all species of yeasts are yet OD) known to produce spores of this kind, although it is a ee) & characteristic pos- sessed by a large Q) GD number (Fig. 35). Botanists divide F!G.35. Three species of yeast each contain- yeasts into two a al divisions in accordance with their power of producing such spores. The genus Saccharomyces includes yeasts which produce spores, while the genus Zora includes those that do not. The number of spores formed in a single yeast cell is not always the same, although commonly three or four. It may not always be the same for the same species of yeast. DISTRIBUTION OF YEASTS 63 “WHERE YEASTS ARE FOUND From the facts just mentioned it will readily be under- stood that yeasts have a wide distribution, even though they do not grow luxuriantly except in sugar solutions. The spores are excessively minute and are capable of being thoroughly dried without injury, in which condition they will remain alive for months. These spores are easily blown by the winds and distributed far and wide. Even the bodies of the yeast cells in their resting stage, before they have produced spores, may be dried, and for considerable time suffer no injury. These dry yeast cells will keep for weeks and sometimes for months without losing their power of growth. The commercial dried yeast cake, which will be referred to presently, contains not yeast spores but simply dried yeast cells. These are still alive and remain for a long time capable of growing if placed in proper conditions of food and moisture. Such dried yeast cells are very light and easily distributed by currents of air. In such dried form yeast is distributed in dust by the winds, and may be found almost univer- ~ sally present over the surface of the earth, except in the middle of oceans and deserts. Elsewhere the air, the soil, and the water are practically sure to contain yeast in greater or less abundance. Such yeast plants, or yeast spores, blowing around in the air have sometimes been called wild yeast, a name quite convenient for distinguishing plants which are indiscrimi- nately scattered in the air from those which we cultivate in great masses for purposes of brewing, bread making, etc. 64 BACTERIA, YEASTS, AND MOLDS Spontaneous Fermentation. These wild yeasts are so common in the air that they are sure to be present in most localities, and they fully explain certain phenomena of fermentation that seem at first sight somewhat puz- zling. Almost any sugary solution will containthem. If the juice of an apple is squeezed from the pulp, it forms a sweet liquid which tastes at first almost exactly like the apple from which it is taken. But if it is allowed to stand in a warm place a fermentation begins in it which rapidly changes its character, pro- ducing in a few hours what we call cider. A typical alcoholic fermen- tation has started, just as truly due to the growth of yeast as are similar fermentations in a brewery. Since ee the yeast has not been planted con- Fic. 16 Wild yeast rom sciously in the cider, the fermenta- the juice of an apple, tion must be due to the wild yeasts which causes the fermen- which find their way into the juice, tation of cider, either before it has been squeezed from the apple pulp or afterwards. The apple has been growing in the air for many weeks, and the wild yeasts have had plenty of chances to lodge on its skin. When the juice is squeezed from the pulp it is sure to contain these yeasts, and they promptly start a fermentation (Fig. 36). In a similar way other spontaneously fermented prod- ucts are made from the juice of various plants or fruits; for any sweet juice from such natural sources will be sure to become inoculated with wild yeast and will consequently undergo fermentation. This fact has been learned by almost all people from experience. Most savage tribes SPONTANEOUS FERMENTATION 65 have learned to make fermented drinks from the juices of plants or fruits by simply collecting the sweet liquor and allowing it to stand until it ferments. These wild yeasts explain another phenomenon occa- sionally seen in the household. The housewife finds that some of her preserved fruits or jellies at times undergo an alcoholic fermentation. This is quite different from molding or decay, and is‘ found only in sugar-holding materials. The preserve develops a peculiar, sharp, pun- gent taste, easily recognized but difficult to describe. It is particularly liable to occur in jellies, partly because they contain much sugar, and partly because, even when covered in jelly tumblers, they are still somewhat exposed to the air and hence are liable to inoculation with wild yeast. Sometimes this phenomenon is also found in con- densed milk and in canned foods that have not been properly protected. It is not uncommon to find a similar fermen- tation occurring in certain types of sugar. Maple sugar which is kept in the pantry for weeks, until it becomes moist, may ferment and develop the peculiar sour taste characteris- tic of this phenomenon. In all such cases the trouble is due to the presence of the wild yeasts which are floating in the air, and which settle and multiply upon any food suited to their growth. These wild yeasts are so sure to be present in the air that it is very difficult to protect a fermentable mate- rial from their action unless the air is completely excluded. Such wild yeasts do not, of course, live permanently in the air, since the air would itself furnish no food for them. They live and grow in the soil, in decaying fruit on the ground, on the surface of fruit on the trees, and in a variety of other places. The air simply distributes them. 66 BACTERIA, YEASTS, AND MOLDS Foop REQUIRED BY YEAST All common species of yeast require sugar for food, and therefore will not grow rapidly unless sugar is pres- ent in abundance. Bread dough ferments because it con- tains some sugar. Flour itself contains a large amount of starch, which is not fermentable; but in the bread dough some of the starch is changed to sugar by a chem- ical process, so that fermentation is possible. Almost all sugar solutions furnish a proper medium for yeast growth, provided the solution is not too dense. Yeast cannot live upon absolutely pure sugar, since it needs certain other materials for food; but all natural sugar solutions, such as molasses, grape juice, etc., contain quite enough other material for the yeasts to feed upon, and they ferment readily enough. A high percentage of sugar is injurious to the growth of yeasts, a fact that explains why almost anything can be preserved if it is saturated with a large amount of sugar. (See Preserves, p. 163.) Food is required for yeasts during the fermentation, since they are growing and rapidly increasing in abun- dance. The simple presence of yeasts produces no fer- mentation. If anything prevents the growth of the yeast plants, no fermentation occurs, and it is always found that the yeast increases in bulk during the process. In the large fermentative industries there is consequently pro- duced a large quantity of yeast, which accumulates in bulk at the close of the fermentations, This material has been mostly a waste product, although a considerable amount of it has been utilized for bread raising, as shown -in the next chapter. Recently a new FOOD OF YEAST 67 use for such masses of yeast plant has been suggested. The yeast mass must contain considerable food material, and the question has been raised whether it is not pos- sible to utilize it as a food product. By simple means extracts of such yeasts have been made and have lately been placed upon the market. These materials, known as ovus, wuk, and szvzs, have not yet appeared in America but are found in the European trade. They have a value almost the same as that of ordinary beef extracts. They make an appetizing bouillon which may be a useful stimu- lant, but since they are only extracts, they contain practi- cally no real food. They may therefore easily take the place of such substances as Liebig’s beef extract and similar products, but like them they do not contain real food and must not be regarded as nutritious. CHAPTER VI YEASTS IN THE HOUSEHOLD As Enemies. Yeast must, in general, be looked upon as the housewife’s friend, since in almost all its relations to household affairs it produces only desirable results. Ina few instances we find yeast producing trouble. Its occa- sional presence in jellies and preserves has already been noticed, as well as in the fermentation of maple sugar. Any sirup containing fruit sugar, cane sugar, or beet sugar may undergo spontaneous fermentation in our homes. In dairy products yeasts occasionally produce mischief, since the bitter tastes of milk and cheese are sometimes caused by their growth. This will rarely if ever trouble the housewife, although it may cause mis- chief for the dairymen. It is only in the fermentation of sugary substances, like jellies and sirups, that the house- wife is troubled with undesired fermentation. One prac- tical suggestion in this connection may be of use. Since boiling will kill yeasts, any material which shows the easily recognized sign of fermentation—the peculiar, sharp, pungent taste can be preserved from fuither injury if it is merely heated to the temperature of boiling. No further fermentation will then occur, provided the subse- quent entrance of yeast is prevented by protecting the material from the air. If the material cannot be heated, there is no satisfactory remedy for a fermentation once started. 68 YEASTS A SOURCE OF ALCOHOL 69 As Friends. Yeasts must usually be looked upon as servants rather than as enemies. They are the allies of the housewife in a number of directions. We have noticed above that when they grow in sugar solutions they give rise to two new substances, carbon dioxide and alcohol, and in various domestic affairs sometimes the one, sometimes the other, and sometimes both of these products are utilized. Tue Use oF YEASTS AS A SOURCE OF ALCOHOL The alcohol produced by yeasts is the foundation of the great fermentative and distillery industries, for common yeasts are the agents which produce the alcohol found in all alcoholic beverages. The fermentative industries, of immense extent all over the civilized world, are dependent upon yeasts. In the manufacture of fermented and dis- tilled liquors these little plants are used in all cases for the production of alcohol out of various sugar solutions. The fermentative industries, therefore, involving the invest- ment of hundreds of millions of dollars, are founded upon the growth and powers of these microscopic plants. The struggle with gigantic evils resulting from these industries forms one of the greatest problems of civilization. This, however, is a matter which does not belong to our immediate subject. In breweries and distilleries some material containing sugar (molasses, preparations from rye, corn, barley, etc.) is inoculated with a quantity of yeast, a species being chosen which experience has shown to be well adapted to the purpose. The mixture is warmed slightly and a 7O BACTERIA, YEASTS, AND MOLDS vigorous fermentation is started. The fermented mass may subsequently be used directly for a beverage — fer- mented drinks, like beer, ale, etc. — or the water may be partly separated from the alcohol by distillation, produ- cing a liquor with a much higher percentage of alcohol, — the distilled liquors, like rum, brandy, whisky, etc. In the making of wines the process is, in a way, simpler, and reliance is usually placed upon the wild yeasts which produce a spontaneous fermentation. The skin of the grape becomes the lodging place of numerous micro- organisms which collect there while the grape is growing. These include molds and bacteria as well as yeasts, and when the juice is squeezed from the grape it is certain to contain some of this wild yeast. Fig. 37 shows some of the wild yeast thus spontaneously inoculated into grape juice. The juice is set aside and a spontaneous fermen- tation begins. The fermentation is not very vigorous and may require many weeks for its completion. In recent years some vintners have adopted the plan of adding to the grape juice cultures of chosen varieties of yeast for the purpose of hastening the fermentation and making it more reliable. The success of the plan is still somewhat doubtful, and this method of wine making has not been very widely adopted up to the present time. So sure is the grape juice to contain yeasts that unless some means of preventing their growth is adopted fer- mentation cannot be avoided. In making what is called unfermented grape juice the yeasts are destroyed by heat. The grape juice is heated to a temperature of about 170° for a few minutes. This operation is usually per- formed twice, after which the wine is bottled and sealed. YEASTS A SOURCE OF ALCOHOL 71 The process is really the same as that of preserving food by canning, which will be described later, the only essential difference being that the grape juice does not require boiling for its preservation. It will be noticed from Fig. 37 that there are other organisms besides yeasts upon the grape skin. These may have some effect upon the wine, but very little is known in regard to the matter. In the household yeasts are occasionally used in the same way, solely for the alcohol they develop. This use is practically confined to the manufacture of a few of the homemade wines which are produced from juices of fruit such as grapes, elderberries, blackberries, currants, rasp- berries, etc. Cider also is an apple wine. The principles in the manufacture of these homemade wines are the yy, 37- Organisms found upon the same as in the production of — skin of a grape.and concerned in the commercial wines. The the fermentation of wine. fruit juice, which contains a considerable quantity of easily fermentable sugar, is expressed from the fruits and mixed with water. Commonly the fruit juice is not sweet enough, particularly if a sweet wine is desired. In the manufac- ture of most homemade wines, therefore, sugar is added. The amount varies widely with the kind of fruit used, being greater for sour fruits, and it varies also according to whether a sweet or sour wine is wanted. The juice is then left to ferment spontaneously under the influence of 72 BACTERIA, YEASTS, AND MOLDS wild yeasts. The juice must not, of course, be heated, for this would kill the yeasts and prevent fermentation. The fermentation is not very vigorous, and the amount of alcohol developed not very great. After the fermenta- tion has about stopped, the wine is placed in bottles or in closed casks. The time required for fermentation may be a few weeks (currant wine) or many months (grape wine). In making cider nothing is necessary except to press the juice from the apples and allow it to ferment sponta- neously, Fermentation in any of these cases might be hastened by the addition of yeast. This is occasionally done, but is not a common practice. Whatever be the source of the yeast, the process of wine making is simply an ordinary fermenting of the sugar. The carbon dioxide that is produced is allowed to pass off into the air undisturbed during the fermentation, and the liquid gradually becomes filled with alcohol. The final result is the wine, which always contains alcohol in small percentage. After the yeasts stop growing, bacteria may develop in the product and cause further changes, so as to injure its taste, or even totally change its nature, as in the formation of vinegar. (See Chapter IX.) Tue Use or YEASTS AS A SOURCE OF CARBON DIOXIDE The chief use of yeasts in the household is not to pro- duce fermented drinks but to raise bread. The raising of bread by means of yeast has been brought to a state of great perfection, so that the method of producing a desir- able fermentation in bread dough by means of this product YEAST AS A SOURCE OF CARBON DIOXIDE 73 is now extremely simple. But it has taken many centuries of experiment and trial to understand the subject well enough to bring it under proper control. In all nations, and apparently in all ages, people have been accustomed to make bread from meals obtained from the different kinds of grain. The earliest method of cook- ing such material was simply to mix it with water and then bake it, the result being a rather hard, tough material known as anleavened bread. The next step consisted of a spontaneous raising of the dough. If dough is left in a warm place for a number of hours, it becomes somewhat swollen with gas, appears lighter in character, and when baked produces a type of bread more easily masticated, better in flavor, and more easily digested. Flour from most cereals, if mixed with water and kept for a few hours in a warm place, will undergo a fermentation, due to the wild yeasts that may have found entrance to the meal. This method of fer- menting the dough gave the first form of ratsed, or leav- ened bread. Very early, even before historical records, it was dis- covered that a little of the dough thus raised would serve as a starter for a second batch, resulting in a quicker and more satisfactory raising than that obtained by spontane- ous fermentation. This was known as leaven, and as far back as the time of Lot we read of leavened and unleav- ened bread. The Egyptians also knew of this process. Leaven has been used from those early days to the pres- ent time. Even to-day leaven consists of a little dough which has already fermented and hence contains yeasts, and which is saved to be used in fresh dough for the 74 BACTERIA, YEASTS, AND MOLDS purpose of starting fermentation. Although its use has largely given way to cultivated yeast, it has been employed in the baking of bread up to very recent times, and to a limited extent is still used in France. The difficulty with leaven is that its action is unreliable. The leaven contains bacteria as well as yeast, and these may make the bread sour, or sometimes bitter; and unless the very greatest care is taken in its manipulation the bread pro- duced by means of it is not good. Only very skillful bakers can use it satisfactorily. The use of leaven has, therefore, almost wholly been replaced by the far more easy and reliable method of raising dough with cultivated yeasts. The use of yeast instead of leaven in bread making is also old. Inthe time of the Roman empire it is apparent, from a few references in literature, that the use of yeast was understood. It is stated that the Romans in baking their bread sometimes used a leaven made of grape juice and millet for the purpose of hastening fermentation. We have already seen that grape juice is sure to contain yeast, and this phenomenon, whose nature the Romans, of course, did not understand, is perfectly intelligible to-day. The Romans were unconsciously using yeast for raising their bread. The early bakers soon learned to use yeast in a more accurate and satisfactory manner, and from the time of Rome down through the centuries the use of cultivated yeast products for the purpose of raising bread was more or less common. The methods of pro- ducing and cultivating yeast during these various ages are not known at the present time. It is known, however, that later the use of yeast declined, and bakers returned METHODS OF OBTAINING YEAST 75 to the old method of using leaven. In the seventeenth century the use of yeast began again, and from that time on it has been used more and more widely. As methods of cultivating yeast developed it became pos- sible to obtain a more reliable product, and as the relia- bility of the product increased so did its usefulness in a pro- portionate degree. At the present time yeast has very largely taken the place of leaven in baking, because it has proved easier to handle and more reliable in its results. METHODS OF OBTAINING YEAST The original source of all forms of cultivated yeast is wild yeast, which, as we have seen, may easily be obtained by exposing any sugary solution to the air. To obtain such yeast in quantity sufficient for the purposes of house- hold fermentation, various devices have been practiced. Some of these, though little used at present, are instruct- ive. A very interesting method of obtaining yeast called “salt raising’ was frequently practiced by housewives before the introduction of compressed yeast. To a quan- tity of milk was added a little salt, sufficient to delay the growth of the common bacteria which otherwise quickly sour it. The milk was then placed in a warm place for several hours. The yeasts which found entrance from the air were not injured by the salt, and grew rapidly. The milk soon began to froth from the carbon dioxide thus developed. This material was then used to mix with the dough for the raising. The method here described has nearly gone out of use, and no study has been made of the kinds of microérganisms actually concerned in the 76 BACTERIA, YEASTS, AND MOLDS process, though it probably involved both yeasts and bac- teria. It is interesting to-day simply because it was a method of utilizing the wild microérganisms for the pur- pose for which we now use cultivated yeasts. Other devices obtained by spontaneous fermentation have frequently been practiced. Bakers sometimes make a brew which is allowed to ferment spontaneously, and use the product for bread raising. In making the Scotch barms, a brew is prepared containing hops and flour, with other ingredients, and this, at least in making “ virgin barm,” is allowed to ferment spontaneously. In all such cases yeasts are obtained, but they are always mixed with bacteria, which may materially inter- fere with their successful working. The uncertainty of results due to these impurities has led to cultivating yeasts especially for household purposes. Cultivated yeasts are simply wild yeasts from the air which have been freed from impurities and planted in some pure food material, where they grow in abundance, giving finally a mass of pure yeast. Cultivated yeasts are now used almost universally by all bread makers because of their greater reliability. FERMENTING PoweER OF DIFFERENT YEASTS The cultivated yeast used to-day in bread raising has been gradually selected from a large variety of species. The microscopist recognizes many different kinds of yeasts, varying in their microscopic appearance, their rapidity of growth, and their power of producing fermen- tation, as well as in other important characteristics. Most FERMENTING POWER OF DIFFERENT YEASTS 77 of them will raise bread, but some of them are poorly adapted to this purpose. Some of them, like brewer's yeast, act so slowly that the bread will not rise rapidly enough. The use of yeast in bread making is dependent entirely upon its fermenta- tive power, and con- sequently the value of any type of yeast will depend upon the energy of its fermentation. Some types of yeast pro- duce a more vigor- Fic. 38. Three fermentation tubes inocu- ous fermentation lated with different varieties of yeast, show- than others. The indicated by the amount of gas collected in cake of compressed the closed tube. The tube on the right was yeast, for example, inoculated with dried yeast, the middle tube : with brewer’s yeast, and the left-hand tube produces a more vig- ; pier 2 with compressed or distillery yeast. ing the differences in fermenting power, as orous fermentation in bread than either the brewer’s yeast or the dried cake. The relative value of the three types in fermenting flour is shown in Fig. 38. In each tube was placed a mixture of flour and water so as to fill completely the closed arm on the right. Each was then inoculated with a different yeast, the same quantity in each. As they fermented the sugar in the flour, the gas given off collected in the closed arm as shown, and the vigor of the fermentation 78 BACTERIA, YEASTS, AND MOLDS may be inferred from the amount of gas produced. It will be seen that the tube on the left has in the inclosed arm a much larger amount of gas than is found in either of the other samples. This tube was inoculated with a dis- tillery yeast (compressed yeast), and the experiment shows that this type of yeast has a greater fermentative power upon flour than either of the other two forms. It sug- gests also that this yeast will be the most satisfactory for the ordinary domestic purpose of bread raising. There are also other factors concerned in the choice of a proper species of yeast. Some kinds of yeast give a sour or otherwise unpleasant taste to bread, and others give to the bread an undesirable color. From the many varieties of yeast which might be used for this purpose certain ones have been chosen by the brewers as par- ticularly well adapted for their type of fermentation ; others are commonly used in distilleries. But this does not necessarily make them the best for bread raising. A long experience in baking has resulted in the selection of the type best adapted for bread raising, and this is a species that grows quickly in dilute sugar solutions and hence raises the bread in a few hours. At the same time it gives rise to a pleasant, agreeable taste, and pro- duces no color. Consideration of all these phenomena has been clearly essential in selecting a yeast which is best adapted for bread making. All of the yeasts used by brewers and distilleries to-day belong to the same species, and this species is also the best for bread raising. But although all one species theré are several quite distinct varieties having different’ fermenting powers. DIFFERENT KINDS OF YEAST 79 DIFFERENT KINDS OF COMMERCIAL YEAST PREPARATIONS In the early periods of bread making there were no means of obtaining pure yeast. Gradually, however, we have learned to cultivate the yeasts by themselves, until at the present time there are quite a number of methods for producing tolerably pure masses of yeast. The chief preparations of this sort are given in the following pages and all one species, known as Saccharomyces cerevisie; but although belonging to one species there are a number of varieties differing in several characters. Compressed Yeast. At the present time the yeast most commonly used by the housekeeper is the compressed yeast cake. This well-known commercial article consists of a soft, somewhat soggy material, composed of large quantities of yeast plants mixed together with a certain amount of starch and a varying quantity of other material. T&is yeast is originally a distillery yeast, which the manu- facturers of certain Bohol products sow in large vats containing materials upon which the plant feeds readily. The yeast grows vigorously and after a few hours collects as a scum on the surface of the vat. This is removed, washed, and the water partly removed by heavy pressure ; then the mass is formed into cakes and sold to the public. This compressed yeast is the most convenient and reli- able type of yeast culture that has been produced. In the fresh cake nearly all of the yeast plants are alive and vigorous, and the results obtained from their use are almost uniformly satisfactory. Compressed yeast has one disad- vantage: it will not keep long, and hence must be used 80 BACTERIA, YEASTS, AND MOLDS while fresh or the proper results will be lacking. If the yeast cake is kept for a day or two only, the plants begin to die, and after three or four days only a small number of them may be left alive. Such yeast when a few days old will not produce as quick a raising of the bread as the fresh cake. More than this, a result is frequently experienced in old cakes that is worse than the loss of activity. The commercial compressed yeast is never a pure yeast, but contains a variety of other microscopic plants, among which are bacteria as well as other yeasts. These other organisms are liable to grow in the cake if kept for a few days, The yeast may even decay, which indicates an excessive growth of bacteria; but if it does not decay it is quite certain that in an old cake other kinds of yeast or bacteria are relatively more abundant than they are in the fresh cake. When such an old yeast cake is used it may give rise to undesirable fermen- tations in the bread, resulting in unpleasant flavors. If it is necessary to keep a compressed yeast cake some days before using it, it is best preserved by placing it in cold water and keeping it in an ice chest, but it should never be allowed to freeze. Where the compressed yeast cake can be obtained fresh, however, it is the most convenient form in use. It is so cheap that the expense need not be considered in the household, where only a small amount is needed. But where large quantities of bread are to be made, com- pressed yeast is rather expensive, and it may be cheaper then to brew one’s own yeast. Consequently bakers long adhered to their own methods of making yeast, to be referred to presently, instead of depending. upon the DIFFERENT KINDS OF YEAST 81 commercial product. For the ordinary housekeeper the bother of making the yeast brew is so great, the results so unreliable, and the expense of compressed yeast so slight, that the latter is now almost universally used. To-day many bakers have given up making their own yeast brews and depend upon compressed yeast. Dried Yeast. A second type of com- . mercial yeast is the dried yeast cake. This is prepared by cultivating yeast, mixing the product with certain ingredients, chiefly starch, pressing into cakes, and then drying the product at a low heat. The drying perhaps injures or kills some of the yeast plants, but a great many of them remain uninjured, and may be found for a long time in the dried yeast cake, still alive and capable of growing if placed under proper conditions (Fig. 39). In order that they may begin to grow again they must be mois- tened, and in using a dried yeast cake it is best to soak it in warm water to which has been added a small amount of sugar. The sugar furnishes food for the yeast plants, and by soak- ing them in warm water they are soon brought to a con- dition of growth, so that when added to the bread dough they readily enough produce a -fermentation (Fig. 40). The dried yeast cakes are not quite so convenient to use as the compressed, but a little experience will enable Fic. 39. Yeast from a dried yeast cake. Fic. 40. The same yeast after a few hours’ growth. 82 BACTERIA, YEASTS, AND MOLDS any one to obtain good results with them. Their great advantage is that they need not be absolutely fresh. The cakes may be preserved for many weeks or even months, and their powers will not be destroyed. They cannot decay or mold, since they contain no water. It is always well to remember, in using them, that the drying of the yeast destroys some of the yeast plants and in time kills them all. If such a yeast cake is examined week after week, an increasingly smaller number of living yeast plants will be found, and finally they will all disappear. The fresher the cakes are the better, and those that are very old are useless. But in spite of this fact these dried yeast cakes may be kept for many weeks, and for persons who have not a ready access to a market they are much more convenient than the compressed cakes. Sometimes yeast is prepared in the form of a dry powder. It is not a very common form, and the statements made concerning dried yeast cakes will apply equally well to yeast powder. Brewer’s Yeast. Yeast has frequently been sold in a liquid form by brewers to bakers, to be used in raising bread. Yeast from such a source is different in variety and action from that of the compressed or dried yeast cake. It grows in the brewer’s fermenting vats, either as the “top” yeast or the “bottom” yeast. The former grows as a scum on the top of the vat, while the latter sinks to the bottom, the former alone being used for bread raising. The first that appears on the surface of the vat is commonly removed, since it is liable to be filled with dirt and harmful bacteria. The flavor of bread raised with brewery yeast is a little different from that raised by YEAST BREWS 83 other kinds, and is sometimes slightly bitter, thus explain- ing the difference sometimes noticed in the flavor of baker’s and homemade bread. This type of yeast does not pro- duce so vigorous a form of fermentation in flour as com- pressed yeast, and is less satisfactory in a household. Its use even by bakers has largely ceased. Cultivation of Yeast Brews. When one is near a mar- ket, by far the most convenient method of obtaining yeast for bread making is to purchase the compressed cake; but when one is far from market a fresh supply is not easily obtained. Moreover, we have noticed that if yeast is needed in large quantities the compressed yeast is some- what expensive. It is then certainly cheaper and may sometimes be more convenient to brew one’s own yeast. Brewing yeast is a very easy process if one will exercise a little care. First one prepares a mixture known as the dvew, in which the yeast will grow readily; and then he inoculates this mixture with a small quantity of yeast from some good source and allows the material to grow. Many varieties of mixtures are in use for the development of yeast. Two good formule are as follows. (1) 1 lb. potatoes (2) % Ib. of malt 3% oz. hops ¥% oz. of hops 1 gal. water 1 gal. of water To prepare the first of these mixtures, boil the potatoes and remove the skins; boil again until thoroughly soft, and then mash finely. Meantime the hops are to be heated with the water to nearly the boiling point for a couple of hours, to dissolve the hop extract. After this the 84 BACTERIA, YEASTS, AND MOLDS liquid is to be strained and mixed with the mashed pota- toes. It is well to boil again for a few moments to destroy any microscopic organisms (bacteria or molds) that may have found entrance into the brew during its preparation. The material is then to be cooled and may be allowed to ferment spontaneously. But, since the results are then unreliable, there is usually added to it, after it is cooled to the temperature of 70° to 80°, a small quantity of pure yeast from some reliable source. The whole is to be stirred occasionally and allowed to stand until the yeast has developed for a few days. The yeast will then be present in large quantity in the brew, and can be used for any desirable purpose. In making the second of the above brews, the process is nearly the same. The hops are steamed or heated with the water, as in the first case, and then mixed with the malt according to the proportions given in the formula. The subsequent treatment is identical in both cases. Some such method of preparing yeast was in former years almost universally used for baking. Brewing yeast is inexpensive, simply requiring a little care; but with the introduction of the convenient compressed yeast at a small price this method of making yeast has practically disap. peared from the household. It is still retained, however, in some places where large quantities of yeast are used. The hops are added to these brews, not as food for the yeast, but for two other purposes: (1) They give a slight nutty flavor which is subsequently imparted to the bread, somewhat improving its taste. (2) The extract of hops is a partial antiseptic, in a measure preventing the growth of bacteria, though not injuriously affecting yeast. Without YEAST BREWS 85 the hops various mischievous bacteria would be almost sure to develop in the brew, injuring or perhaps ruining it. The slimy-bread bacterium, for example (see page 93), is liable to grow in these brews, but the hop extract has a decidedly antiseptic power against it. By a method somewhat similar to the above, breweries and distilleries cultivate yeast; but in these large estab- lishments, where there is a demand for large quantities of yeast of the highest grade, a care is given to the brewing impossible in the home. The brewer uses a microscope to test his product, and exercises a care in cultivating his yeast which insures its purity. Yeast from such sources is therefore more reliable than any other, and consequently most yeast in use to-day comes from breweries or dis- tilleries, or from institutions where it is grown upon a large scale. Home brewing of yeast is unreliable and unsatisfactory. CHAPTER VII BREAD RAISING; FERMENTED LIQUORS Wuat 1s BreapD Ralsinc? The method by which yeast makes bread light is very simple and easily understood. There is present in the bread dough, at the start, a small amount of sugar which comes from the flour; but there is, in addition, a con- siderable quantity of starch, and with the starch there is also present in the flour a small amount of a material known as diastase. By the action of this diastase in the dough, part of the starch is converted into sugar. Thus there is present in the dough, after it is mixed, a sufficient quantity of sugar to furnish proper ferment- able material for the yeast. The baker mixes the fresh, active yeast with the dough, and places the whole in a warm place where the yeast will be stimulated into active growth (Fig. 41). 86 Fic. 41. Recently mixed dough in- oculated with yeast, but before the yeast has grown. WHAT IS BREAD RAISING 87 The yeast begins to feed upon the materials in the dough and ferments the sugar, producing carbon dioxide and alcohol. Both of these materials remain for a while in the dough, the alcohol dissolving in the water, and the carbon dioxide accumulating as a gas in small bubbles. The dough is so sticky and heavy that it is not possible for these bubbles to rise up through the dough as it does in ordinary fermented liquids (Fig. 31). The gas, there- fore, simply collects as small bubbles in the midst of the dough, causing the dough to swell. This is the so- called razstng of the bread, and the bread maker must learn from experience when it has progressed suff- ciently. After the dough Poe has been properly “raised” yg, 42. The same dough after by the yeast, it may be yeast has grown and caused the seen to be filled with holes dough to swell up by the accumu- occupied by the gas bub- bles (Fig. 42). Now, after the proper kneading, it is put in the oven for baking. The heat of baking drives off the small amount of alcohol which is contained in the bread. The heat also expands the bubbles of gas so as to enlarge the little holes in the dough, thus causing it to swell still more; but while this is being done the heat hardens the dough into the firm texture of the baked bread, and the holes previously occupied by the lation of carbon dioxide. 88 BACTERIA, YEASTS, AND MOLDS carbon dioxide gas are left as pores in the bread (Fig. 43). This makes the bread light and porous, and gives it the character that every one is familiar with in properly raised bread. If it were not for these holes, the dough would be a hard, tough mass, difficult to bake and more difficult * to digest. The purposes of the raising of bread by yeast are three. 1. It makes. the ma- terial /éghter, i.e. more porous, and hence easier of mastication and more palatable. 2. Itrenders it move ai- gestible, because the por- ous material is more easily Fic. 43. The same material after bak- acted upon by the digest- tog tin 4 My julces than the more solid unleavened bread. 3. The yeast imparts a certain flavor to the bread which enhances its value. This flavor, due to yeast, is well shown by the difference in the flavor of bread raised in the ordinary household and that sometimes raised by bakers, where a different species of yeast is used. That the flavor produced by yeast is an important factor may be realized also by comparing the flavor of bread raised by yeast with that made light by chemical or mechanical means. Any process which will fill the dough with bubbles will make it light. In one type of bread, known as aévated bread, the spaces or cavities in RELATION OF BREAD RAISING TO TEMPERATURE 89 the dough are produced by mechanically mixing air with the dough. The result is a bread that is light enough but lacks the peculiar flavor present in ordinary raised bread. In another type of bread (guzck bzscuzts) chemical means are relied upon to produce the gas. A small quan- tity of cream of tartar and saleratus is mixed with the dough. These two materials act upon each other chem- ically and give rise to a quantity of carbon dioxide gas, which appears very quickly, and rapidly fills the dough with bubbles of gas. The dough, when subsequently baked, is light, but has a flavor quite different from that which would be produced in the same dough if it were raised by the action of yeast. No other method of pro- ducing lightness in the dough gives quite so good flavors as can be obtained by the use of yeast, and none is thought to make bread quite so easy of digestion. RELATION TO TEMPERATURE The growth of yeast, and hence the raising of bread, is very closely dependent upon temperature. Yeasts grow readily in warm temperatures, less readily in low tempera- tures, and not at all if the temperature is in the vicinity of freezing. Common yeast grows best if kept between 75” and go’ F, At higher temperatures the yeast does not produce such good results, since certain other injurious microérganisms (éacteria) are then likely to grow. If the dough is kept at a temperature above 90°, there is almost sure to be trouble from the growth of undesired organisms which give rise to unpleasant flavors. Bread made from such dough is very apt to be sour. The go BACTERIA, YEASTS, AND MOLDS temperature should be higher in winter than in sum- mer, owing partly to the fact that flour in winter is quite sure to be cold and to require some time to become warm. In winter a temperature of 95° is not too great for the proper raising of the dough, while in summer a temperature of 70° is more satisfactory. In the raising of bread dough it is always far better to use a ther- mometer and to determine the exact temperature. This is rarely done in the ordinary kitchen. It is more com- mon to place the dough near the stove and trust that the temperature will be close enough to that desired. It is not possible, under these circumstances, to depend absolutely upon the results. In the majority of cases the dough is fermented satisfactorily, but bad batches of bread from this cause are a frequent experience of the housewife. To produce uniform results it is quite necessary to use a thermometer, and then the dough may surely be kept within the limits of temperature above mentioned. The length of time for yeast to grow in the dough before baking is dependent upon the temperature of the fermen- tation; but it is important that it should not be too long. If the temperature is low (below 70°), so that it requires a longer time than usual for the dough to rise sufficiently, the texture of the bread is apt to be crumbly and brittle, and a sour taste is very likely to develop, due to the growth of other microdérganisms besides the yeast. If, on the other hand, the bread rises too quickly, owing to too high a temperature, an abundance of gas is produced which makes the dough rise rapidly; but the bread will be inferior in flavor, texture, and color. The best results IMPURITIES IN COMMERCIAL YEAST gi are obtained by a moderately active growth of the yeast, which will produce a sufficient amount of lightness in the dough in the course of eight or ten hours. IMPURITIES IN COMMERCIAL YEAST One factor largely determining the value of commercial yeast is its purity. It rarely or never happens that a yeast cake, or yeast culture of any form, is composed purely of yeast. There is almost certain to be mixed with it a quantity of bacteria. Frequently there is also present a variety of mold spores, and especially in summer the yeast cake is likely to contain other species of yeast besides the one desired for bread raising. These impurities may be abun- dant or scanty in any cake of yeast. If they are present at all, they may produce trouble, but this will depend upon circumstances. The yeast plants themselves are present in such overwhelming proportions that, under ordinary cir- cumstances, the impurities get little opportunity to develop. If the raising is conducted at a proper temperature, the impurities will rarely do much injury. In the common use of yeast, therefore, in spite of the fact that various bacteria and mold spores may be mixed with the dough when the yeast is added, the bread rises in a normal way, and the impurities produce no trouble. These foreign bacteria in the yeast cake are quite sure to increase with its age. While the yeast plants do not multiply in the compressed yeast cake, the bacteria are almost sure to do so, especially if the cake is kept in a moist condition for some days before using. An old yeast cake is therefore quite sure to contain more of these 92 BACTERIA, YEASTS, AND MOLDS impurities than a fresh one. Moreover, in an old cake, as we have seen, the number of living yeast cells is less than in a fresh one, and so the undesirable germs have a better chance to grow in the dough. The use of an old yeast cake is therefore unwise, since the bread may thus be ruined. The fermentation does not progress rapidly enough, the bread must be kept longer at a warm tem- perature, and during this whole period the other yeasts or bacteria have a chance to develop and produce a variety of bad flavors. If one uses fresh yeast cakes, there is little probability that any trouble will arise from the action of the smaller number of bacteria or molds that may be present. Sour Bread. The impurities from the yeast or from some other source do, however, occasionally produce trouble, two types of which are so common as to demand notice. The raising of dough by means of yeast some- times causes it to become sour. The dough rises in the proper manner apparently, but the bread when baked is found to have an unpleasant, sour taste. This is espe- cially likely to happen if the bread is raised too long. By some this sour taste is regarded as an improvement to the flavor. It is due to the development, during the fer- mentation, of certain acids in the dough, which come, not from the action of yeasts, but from the growth of bacteria that are present either in the yeast or flour. It has been a disputed question whether the acid produced is /ac- tic, acetic, or butyric. (Lactic acid is like that formed in sour milk, acetic acid is formed in vinegar, and butyric acid is the acid found in old rancid butter.) It is fre- quently a mixture of all three, but ordinarily it is prob- ably mostly lactic acid. Each of these acids is known SOUR BREAD 93 to be produced by bacteria. Since the acids are caused by bacteria, this subject really belongs to a later division of our discussion ; but its close relation to bread making leads to its introduction at this point. Recognizing that the cause of sour bread is due to the growth of bacteria, it is not difficult to suggest the proper means of avoiding it. Fresh yeasts only should be employed. A good quality of flour should be used, and the dough should be mixed in clean utensils. After mix- ing, the dough should be placed in a clean dish at a proper temperature (75° in summer, 90° in winter), so that the bread will rise in.about eight hours. Dough should never be allowed to ferment too long. Strict attention to these details will commonly remove the trouble. The bacteria which produce sour bread do not, however, come wholly from the use of impure yeasts, for the flour itself is likely to contain some organisms which may cause this trouble. A sour taste is much more likely to be found in bread made from poor grades of flour than in that made from the higher grades. This is perhaps due to the fact that, owing to difference in the method of manufacture, the lower grades of flour contain a larger number of bacteria. The same trouble is also sometimes caused by the use of unclean utensils in the mixing of the dough, or by leaving the dough to rise in a dish not thor- oughly washed. Unclean utensils are sure to have a large number of bacteria attached to them, and these bacteria, becoming mixed with the dough, grow there readily side by side with the yeast. Slimy Bread. In recent years it has been noticed that, a few hours after baking, bread sometimes ‘becomes slimy. 94 BACTERIA, YEASTS, AND MOLDS When perfectly fresh it does not show any sliminess, but after standing a few hours the inside of the loaf appears more or less moist, and shows a slimy texture when broken, looking as if permeated with cobwebs. This trouble is occasionally met with in the household, but more commonly in bakeries. Indeed, sometimes sliminess has become so troublesome in certain bake shops as nearly to ruin the business, the trouble reappearing day after day and prov- ing extremely difficult to remedy. The cause of the trouble is known to be the develop- ment of certain bacteria, one species of which is shown in Fig. 44. These bacteria are capable of growing in the dough, and are not killed during the baking. After the bread is removed from the oven they begin a rapid growth, if the bread is kept warm, and in a few hours produce the trouble de- Fic. 44. A species of bac’ scribed, These bacteria frequently terium which produces slimy bread. come from the yeast, but in some cases, where the subject has been studied in detail, it has appeared that the source is the flour rather than the yeast. Certain samples of flour con- tain these mischievous organisms, and when bread is made from such flour it is difficult to avoid their presence and growth. A change to a new brand of flour will then obviate the trouble. If a housewife should experience this slimy bread fermentation, the proper method of pro- cedure is (1) to use a new brand of flour for bread mak- ing, (2) to sterilize, by methods to be referred to later, all utensils that are used in connection with bread making, ALCOHOL AND CARBON DIOXIDE 95 and (3) to get a fresh supply of yeast. After this the trouble ought to disappear. It is also important to remember that the sliminess only occurs if the bread is kept warm, and hence chiefly in the summer. If the bread is cooled at once and kept in a cool place until it is eaten, the trouble is not likely to manifest itself even though the slimy bacteria are present. The bread is wholesome enough even though slimy. THE UTILIZATION OF BOTH ALCOHOL AND CARBON DIOXIDE In the immense fermentation industries involving the production of deers, porters, ales, etc., both of the products of fermentation are commonly utilized. The general char- acter and effect of beer are due partly to the alcohol pres- ent and partly to the presence of a quantity of the car- bon dioxide, which gives to the beer its sparkle. In the manufacture of such a product the fermentable material, usually some form of grain, is inoculated with a large quantity of a vigorous yeast, a species being chosen that has been found by experience to produce the desired results. A fermentation starts up which progresses rap- idly if the temperature is kept warm, as it is in the man- ufacture of common beer. The fermentation lasts a few days. If the temperature is low, as in the production of the so-called lager beer, the fermentation lasts many weeks, During this fermentation alcohol accumulates in the liquid, and the carbon dioxide gas escapes into the air, forming a froth in the fermenting vat. The yeast increases in amount, and either collects on the surface or sinks to 96 BACTERIA, YEASTS, AND MOLDS the bottom. Most of the yeast is then removed, and the liquid stored in casks or bottles. Here the fermen- tation continues for a time, but rather slowly. Since the vessels are closed the carbon dioxide gas cannot escape, but, accumulating in the vessel, is partly dissolved in the liquid itself. The gas exerts considerable pressure inside the bottle or cask, and when it is opened the expansion of the gas gives rise to the popping of the corks and the bubbling and frothing of the beer; in other words, to the sparkle. Beers are usually drunken while they are toler- ably fresh, and sometimes before fermentation has wholly ceased, though some types of beer are kept for months. In all such fermented products the carbon dioxide is desired no less than the alcohol, since it contributes materially to the flavor of the product. In the production of sparkling wines a similar effect is produced by a sec- ondary fermentation, forming carbon dioxide in the wine after it is placed in the bottles (Fig. 45, 0). For those interested simply in home problems the fer- mentation of beers is of little importance. It is carried on chiefly in the great breweries, where beer is made ona large scale, but only to a very limited extent in the house- hold itself. It has been, however, a somewhat common procedure in certain households to make homemade beer on a small scale. In previous years this was made from certain roots and extracts of strongly flavored plants. For example: home beers have been made from a mixture of molasses and hops flavored with spruce extract; or sugar and ginger with lemon for flavor; or a mixture of sugar, crushed raisins, and lemon; but to-day highly flavored extracts are purchasable at stores for a small BREAD RAISING; FERMENTED LIQUORS 97 price. These flavoring extracts are mixed at home with a quantity of sugar and water (two pounds sugar to ten quarts water). To the mixture is added a considerable amount of yeast (one cake for the above quantity), and the whole material, closed in bottles or other vessels, is then set aside ina warm place for fermentation. Oo The fermenta- ioe tion goes on : ) rapidly, and in ie the course of a ie: \ couple of days a beverage is Neen produced, filled oe with carbon di- . oxide, which causes a bub- i= - bling and froth- Lo, } ing when the t o5t, vessel isopened, Og and containing Fic. 45. Miscellaneous species of yeast. a small quantity «a, S, cerevisie; b, S. pastorianus I, from wine ; ¢, S. pastoria- nus III; d, S. ellipsoideus II; e, S. cerevisia, from beer; of alcohol The Y, S. apiculatus; g, S. minor. amount of alco- hol in such beverages is small if the fermentation is not kept up too long; but in o/d@ homemade beer the alcohol may be considerable. Such home-brewed beer has come to be somewhat extensively used in recent years. In its manufacture it must be remembered that the fermentation, which results 98 BACTERIA, YEASTS, AND MOLDS in the production of carbon dioxide and alcohol, is due to the action of the yeast upon the sugar and not to the beer extract. The extract is added in these cases chiefly to produce a peculiar flavor in the product, which renders it palatable. The commercial beer extracts simply give a pungent taste and perhaps stimulate the growth of the yeast ; but it is the fermentation of the sugar that causes the sparkle due to the carbon dioxide, and any sugary solution will ferment in a similar way if yeast is added. The product is not palatable, however, unless something is present to give it a flavor. The only reason why such homemade beers are less intoxicating than commercial beers is because the fermentation is allowed to continue but a short time, long enough to produce an abundance of carbon dioxide but only a little alcohol. Fermented Milk. A mild fermented beverage is occa- sionally made from milk by means of a yeast. It is called kumiss, and is regarded as useful for invalids, since it is supposed to be more easy of digestion than raw milk. Its preparation is as follows. Into a quantity of milk is placed a little common sugar, — from four to eight table- spoonfuls to a gallon of milk,—and yeast is added just as in homemade beer, one fourth of a cake of compressed yeast in a little water being sufficient fora gallon of milk. The mixture is put in a warm place and fermentation sets in. After twenty-four hours’ fermentation the material is bottled and placed on ice; when cool it is ready for use. The milk becomes slightly soured, giving a taste much relished by some people. It is filled with carbonic diox- ide and contains a small amount of alcohol, and is thus a sort of beer made from milk. It is not much used in this BREAD RAISING; FERMENTED LIQUORS 99 country except for invalids. Other types of fermented beverages, efir, mazoon, and some others, are made from milk by the use of special ferments, always containing yeast, but whose preparation is hardly within the reach of the ordinary household. SECTION III— BACTERIA CHAPTER VIII THE GENERAL NATURE OF BACTERIA Our study of bacteria must be more extended than that which we have given to either molds or yeasts. While molds and yeasts are of significance in the household, the action of bacteria is much more fundamental and universal. Bacteria are far smaller than yeasts or molds (Fig. 46). They are com- monly unknown to the housewife even by name, and rarely does she under- ‘stand that they have any Fic. 46. Showing the comparative size -alation to household of molds (a), yeast (4 and ¢), and bac- feria, 2), economy, or concern her very closely. Few have ever seen them or been aware of their existence. Never- theless they are so constantly at work upon all kinds of food products in the pantry, that the affairs of the house- hold are in a state of more or less constant warfare against these invisible, unrecognized, and unknown foes. They are more serious enemies than molds or yeasts. Chiefly to their presence and activity is due the fact that the preservation of foods, even for a few days, is frequently 100 STRUCTURE OF BACTERIA IOI difficult, while special devices are required to preserve food indefinitely. To the housewife bacteria are of little value and are foes, like the molds, rather than allies, like the yeasts. This does not mean that they have no utility. On the contrary, they are of the most fundamental importance in nature, and it is no exaggeration to say that the very con- tinuation of life is dependent upon their activity. To the agriculturist they are abso- lutely essen- tial. They are the dairy- man’s close Fic. 47. Comparative size of the point of the finest allies, and cambric needle (4), a particle of dust (2), and bac- 4 teria (c). ‘ they are in- dispensable friends of many industries. By their action are produced some of the articles for our tables (vinegar) and also the flavor of butter and cheese. However, these phenomena do not directly concern the housewife, and, with a few individual exceptions, bacteria are her foes. STRUCTURE OF BACTERIA Size. Bacteria are much smaller than yeasts, and only the high powers of the microscope can disclose their presence (Fig. 47). Many are not more than a fifty thousandth of an inch in diameter, and even the larger ones are not much more than a ten thousandth of an inch. But bacteria are far more abundant in nature than yeasts. They are present in great numbers in the earth, 102 BACTERIA, YEASTS, AND MOLDS the air, and the water, and are sure to find their way into every kind of food or anything else that may be exposed to the air. They aré also much more troublesome than molds for two reasons: (1) they multiply with a rapidity that is quite inconceivable; (2) they are quite invisible to the naked eye, and their presence is not suspected until they become numerous enough to produce undesired changes in the material upon which they are growing. As a result they present a vast number of problems to the housewife, which she has dimly seen for years, but for which science has only in the last few years begun to offer solutions. They are much more difficult to handle than either molds or yeasts, because they are smaller, more numerous, and more vigorous, and for these reasons it is almost impossible to exterminate them. It is an impossibility to free a pantry from bacteria and very diffi- cult to guard food from their action. Shape. Bacteria are very simple, and there are such slight differences between the various kinds that in many cases it is quite impossible by microscopic study to dis- tinguish one species from another. The bacteriologist knows to-day that many bacteria which when studied under the microscope appear absolutely identical, are totally unlike in their general characters. It frequently happens that perfectly harmless bacteria cannot by ordinary micro- scopic study be distinguished from those that are very harm- ful. For example, the bacillus which produces typhoid fever cannot be distinguished microscopically from another com- mon but harmless species found in water. For this reason the microscopic study of these plants gives only a small part of the facts that we need to know in regard to them. CLASSIFICATION OF BACTERIA 103 Classification. A consideration of the classification of bacteria is quite unnecessary for the purpose of our work, inasmuch as they are so minute that no one without the aid of a powerful microscope will ever be likely to see these organisms. Their activities are seen on all sides, but the organisms themselves are totally below the reach of our vision. It is sufficient, therefore, to give a few facts concerning their general appearance. Bacteria are the simplest organisms known. They are far simpler than molds and even simpler than yeasts. So minute are they, and so simple in their structure, that very little is known in regard to them at the present time except their general external appearance. They are uni- versally regarded as plants, although many of them are endowed with a power of motion and for this reason might readily be mistaken for animals. Biologists have learned, however, that many plants can move, and they are univer- sally agreed that bacteria must be classed with plants rather than animals. Flagella. The fact that many bacteria are endowed with the power of motion suggests that they must have. locomotive organs, and these, indeed, are easily seen by proper microscopic study. They consist of minute hairs which project from the body of the bacteria. Sometimes there is a single one from one end, sometimes they occur in tufts, and occasionally they may be scattered all over the bodies of the bacteria as shown in Fig. 48. These little hairs are capable of waving to and fro, and by this motion they drive the bacteria through the water. Not all bacteria possess such locomotive organs, and one means by which scientists classify these organisms is by 104 BACTERIA, YEASTS, AND MOLD: the presence or absence of these motor hairs. They are known by the name of flagella. Spherical Bacteria: Cocci. The simplest type. of bac- teria consists of those that are in the shape of a minute sphere. Their size differs somewhat, but they are always extremely minute, and about all that can be said in regard to them is that they are spherical organisms, sometimes possessing flagella and sometimes apparently without them. No internal Fic. 48. Cocci, bacilli, and bac- : teria. a (Coccus), band c (Bacil- structure is known. They Jus), show flagella; d (Bacterium) multiply sometimes in such has no flagella. a way as ore 0So P Be to produce long chains (Fig. 49, a), Oo OO sometimes so as to produce groups of eee fours or groups of eight or sixteen &B , (Fig. 49, 6, ¢, d). The general name UO jd given to spherical bacteria is coccus, and to this name are sometimes prefixed F!6- 49: Cocci.ghow- Saat B ing methods of mul- certain other syllables to indicate certain tipjication. a, Strep- characters. Streptococcus is a name tococcus; 6, Micro- given to cocci forming chains (Fig. 49, “ss ¢ and 4 : 5 Sarcina. a), and Micrococcus to those forming fours or irregular masses as at 5. The term Savcina is the name given to those that form solid masses such as shown in Fig. 49, ¢ and d. CLASSIFICATION OF BACTERIA 105 Rod-shaped Bacteria. These are in the shape of rods of greater or less length. They are usually somewhat rounded at the ends and may be only a little longer than they are broad, or they may be L225 O very many times as long as broad 2, Ses. (Fig.50). When one of these grows rE it lengthens and commonly soon ¢ f divides into two, but they may con- oe tinue to lengthen for a time without Fic. 50. Rod-shaped bac- manifesting any signs of division. ou In such a case they form long slender threads, as shown in Fig. 50, 4. These threads, however, eventually break up into short sections (Fig. 50, c). Some of these rod- shaped bacteria have flagella and are capable of active motion, in which case they form the species of Bacillus (Fig 48, c); others have no flagella and are quite with- out the power of motion, in which case they constitute the species Bacterium (Fig. 48, @). Spiral Bacteria. A third type of bacteria is in the form of a spiral rod, shown in Fig. 51. These, however, are somewhat uncommon and of less fa importance than the others. Like the other forms they may possess e flagella or they may be without 2S them. Multiplication. The growth and multiplication of bacteria is ex- tremely simple and consists in a lengthening of the individual followed by its division. A sphere becomes slightly oval in shape and then divides in the middle to produce two spheres, as shown in Fig. 52, a. Fic. 51. Spiral bacteria. 106 BACTERIA, YEASTS, AND MOLDS One of the rod-shaped forms lengthens itself and divides in the middle and produces two individuals, each of which again lengthens and divides (Fig. 52, 6). The same method is found in the spiral bacteria. This manner of division, which is characteristic of all bacteria, will be seen to be quite different from the method we have already noticed in the yeasts. Indeed, the distinction between yeasts and bacteria is based upon this method of multiplication. The ze) CIC 300 method of multi- plication in bac- 60D) CCTM teria is known as €Oaq Be was : fission, and this d eee sterarnssrmee ] group of fungi are called fission fungi ; Yi in distinction mera oe eer from the yeasts, Fic. 52. Showing the method of multiplication which are called by fission. «w, a coccus form; 4, a short rod; budding fungi. The c,d, and e, showing the method of growth into difference between long chains and the consequent breaking into these two classes sections. eae can be distin- guished only by careful microscopic study, but it is the scientific distinction between the two groups. Spore Formation. Under some circumstances bacteria have a different method of multiplication. Inside of the body of a single individual bacterium appears a little rounded mass which is known as a spore (Fig. 53). This spore may be broader than the rod which produced it, or it may be narrower; but it finally breaks out, the bacterium itself disappearing and the spore then coming out freely in the medium in which it lives. These GROWTH OF BACTERIA 107 spores are capable of subsequently germinating into new individuals like those that produced them and thus continuing the race (Fig. 53, 4). Not all bacteria produce spores, and the question whether any species of bacteria forms spores is a matter of most extreme significance in connection with its func- tions ; for these spores are covered by a little shell which is hard and tough and capable of resisting various adverse condi- tions. Spore-bearing bacteria may be dried without injury, for their spores protect them from destruction. They may be heated to a high temperature, even to boiling, without being killed. Thus the presence of spores will Fig. 53, Showing the forma- make a great difference in the tion of spores. At a is a ease with which any material can _ftee spore and at 4 a germi- 1s 4 nating spore. be sterilized by heat. Bacteria not capable of producing spores are very easily killed by heat, while the spore-bearing forms are destroyed with much greater difficulty. GrRowTH OF BACTERIA Rapidity of Growth. The most striking fact in regard to bacteria is their wonderful rapidity of multiplication ; for upon this are dependent their extraordinary powers. Bacteria growth and multiplication mean the same thing, and the rapidity with which they can multiply is almost inconceivable. Certain. kinds cf common bacteria can 108 BACTERIA, YEASTS AND MOLDS reproduce themselves once every half hour, the result of which is that a single bacterium will have become two in a half hour, four in an hour, eight in an hour and a half, and so on. This increase of progeny by geometrical pro- gression results in the production of descendants with immense rapidity. If the rate of multiplying above men- tioned should continue for twelve hours, the result would be the production of about seventeen million offspring. Such a rapid production as this does not continue very long, through lack of food and other adverse conditions. If it did, the world would soon become filled with bacteria, crowding everything else out of existence. Recognizing that they have this wonderful power of multiplication, we can readily see that bacteria represent a force in nature of almost inconceivable magnitude. This rate of growth is a possibility for a while at least, and in order that such a multiplication should continue it is only necessary that the bacteria should be given proper food and proper conditions. The results are mar- velous. Although they are so small that a single one can accomplish practically nothing in nature, the fact that this single one can in twenty-four hours produce millions of descendants gives to bacteria almost unlimited power. An appreciation of this fact is fundamental to an under- standing of the action of bacteria. Since one in the course of a few hours may become hundreds of thousands, and a little later its progeny may be millions, it is clear that in order to protect any material from the action of bacteria something more is necessary than simply to veduce the number of microdrganisms. If the material . is to be protected from them, every single bacterium must GROWTH OF BACTERIA 109 be destroyed, for if but one be left alive it will require only a few hours for its descendants to become so numer- ous as to be able to accomplish almost anything in the way of chemical destruction. Relation of Growth to Temperature. This great power of growth is dependent upon many factors, most promi- nent among which is temperature. Like all living things, bacteria will not grow at the temperature of freezing or below, but will develop at nearly all temperatures above, some species even growing at14o0.° Certain ,¢ ee species grow best ata : temperature that is not much above freezing ; others grow best at higher fom peratures, Fic. 54. Showing the effect of variations Most of the common in temperature on bacteria growth. a, household types require a single bacterium; 4, its progeny in considerable warmth for twenty-four hours at 50°; ¢, its progeny i in twenty-four hours.at 70°. their proper growth, and the warmer the temperature, up to a certain limit, the more rapid their growth. The relation of temperature to the rapidity of multiplication, for common species, is shown by the accompanying figure (Fig. 54). At a@ is repre- sented a single bacterium; at J is the progeny of this bac- terium when kept twenty-four hours at a temperature of 50°, a little above that of the ordinary ice chest ; at ¢ is the progeny of this bacterium kept the same time at 70°, the ordinary temperature of a living room. A glance at the figure will show what an extraordinary influence a few “mate 110 BACTERIA, YEASTS, AND MOLDS degrees of temperature may have upon the rate of growth of this bacterium. The figure teaches a very practical lesson in regard to the influence of cold in delaying the growth of bacteria and thus protecting food from spoiling. If the temperature is raised too high, it has an injurious action upon the growth of bacteria. Each species of bac- teria grows best at a certain temperature, growing less rapidly if warmed above this point or cooled below it. Most, though not all,. of the bacteria against which the housewife has to contend grow best at temperatures between 70° and 95°. If the temperature is raised above 95°, many cease to grow so rapidly, and at still higher tem- peratures — between 125° and 140° —a large majority are quite incapable of growing at all. At the higher temper- atures food would hardly decay. There are, however, a few species which grow only at very high temperatures, not developing at all unless it is above 125°. It is perfectly evident that all problems connected with the protection of food from the action of microérganisms will be dependent upon the temperature at which the bac- teria grow most rapidly. Food which is kept in an ice chest, although it may be protected from the action of those bacteria which grow only.at room temperatures, will be exposed to other species that grow best at lower tem- peratures. When we remember that some kinds of bac- teria grow at temperatures close to freezing, we can readily see that no method of cooling food short of actually freezing it will totally protect it from decay. Death Temperatures. All bacteria are killed by excess- ive heat, but the temperature which kills them is some- what variable. Bacteria exist, as we have seen, in two DEATH TEMPERATURE IIl forms. One is the active, growing form, in which they . feed and multiply rapidly ; the other is the spore form, in which they are at rest, neither feeding nor growing. In the former condition they are easily killed by moderate heat, a temperature of 140° to 160°, if continued for an hour (usually a much shorter time), being quite sufficient to destroy them. In the form of spores, however, such a temperature has little value in destroying them. Bacteria can resist without being killed a higher temperature than can any other known form of living matter. Spores of certain bacteria can be boiled for a long time without being killed, and if subsequently cooled they will grow and multiply. To destroy the vitality of such spores requires a temperature above that of boiling water, a temperature rather difficult to obtain, at least for liquids, in an ordinary kitchen. It is, however, important to remember that although many kinds of bacteria spores are not killed by a short boiling, a boiling of an hour or two is sufficient to destroy even the most resisting spores. Any material, therefore, that can be boiled for a considerable length of time may thus be thoroughly sterilized, that is, may have all its actively growing bacteria and all its spores destroyed at the same time. This great resist- ance to heat on the part of bacteria spores is a matter of much importance to the housewife, and she should fully realize it. All canning processes, as we shall see, depend upon the destruction of bacteria, and the resistance of spores to boiling is a factor that should always be remembered. A practical lesson to be drawn from these facts is that food heated to Joz/ug in its preparation is thereby, in a 112 BACTERIA, YEASTS, AND MOLDS measure, protected from spoiling, since the bacteria are mostly killed. But if the food is simply warmed, the spoiling is hastened instead of delayed. For example, in making beef tea, if the liquid is boiled, it will keep easily; but since boiling precipitates the proteids and deprives the material of most of its food value, it is better to make it by warming without boiling. Such material decays very rapidly, and, if set on the back of the stove to keep warm, will be spoiled in a short time. Moderate heat hastens bacteria growth. Boiling kills all but spores. Light. Direct sunlight rapidly kills bacteria (except some spores) and daylight in general has an injurious effect upon them in proportion to its intensity. They grow best in darkness. Dust or dirt exposed to sun- light soon loses most of its living bacteria, while in dark cellars, dark corners, and cracks they may remain alive a long time. Hence the rooms in our houses should be kept light. The too frequent habit of closing blinds and using heavy curtains or shutters to keep out the light is a great mistake. Pantries and kitchens should have all the light possible. A sick room particularly should have all possible sunlight; and bright colors for wall paper, curtains, etc., will aid not only in making it cheer- ful but in actually destroying the disease bacteria. Sun- light and fresh air should everywhere take the place of the darkened, closed rooms which have been only too common in our houses in past years. Relation to Air. Most living things require oxygen and therefore demand air for their growth. This is true of a majority of bacteria. Most bacteria like to feed where they can have plenty of air. Hence decay is apt RELATION TO AIR 113 to begin on the surface of things, extending towards the interior. This is not true, however, of all bacteria. Some species can grow perfectly well without air, and others, indeed, cannot grow at all if they are in contact with air. The latter bacteria, which live without oxygen, are known as anaérobic; the former, which demand oxygen, are called aévobic. The aérobic bacteria are by far the most important in the affairs of the household, but the anaé- robic bacteria, on the other hand, produce certain types of putrefaction which are sometimes more serious, inasmuch as the products of putrefaction which take place without air are likely to be more poisonous than those products of decay taking place in contact with the air. We must remember, then, that whereas most bacteria grow best in the air, we cannot protect any material from the growth of microdrganisms simply by keeping air away from it, inasmuch as some species grow perfectly well, and even better, out of contact with the air. Hence, in canning food, it is not the exclusion of air that makes preserva- tion of food possible, but the exclusion of bacteria. Moisture. Like yeast and molds, bacteria require water. Dry food is protected from their action because they cannot obtain water sufficient for their life processes. Bacteria, in general, require more water than molds. Vari- ous materials, if simply damp, will mold or mildew, but they will not support bacteria life unless the amount of water is considerable, 25% to 30% of water being necessary for any growth, and a larger amount still for vigorous growth. Hence they may be expected to grow in all kinds of food which are thoroughly wet, but they will not grow in any of the dried forms of food which we keep 114 BACTERIA, YEASTS, AND MOLDS in our houses, a fact of much importance in connection with the problem of food preservation. Acidity. For still another reason molds and bacteria do not commonly flourish upon the same material. The former, as we have seen, grow best upon acid substances; but most bacteria cannot endure acids, preferring a slightly alkaline food. Hence fruits, which are acid, decay by molding, while meats, which are not so acid or are alka- line, decay by bacterial action. The presence of acid or sourness in food will check its decay. Some food (cran- berries) may be actually too sour for bacteria growth. WHERE BACTERIA MAY BE FOUND We may almost say they are to be found everywhere upon the surface of the earth. This is not strictly true, since a few places seem to be free from them; for exam- ple, the middle of deserts and the bottom of the deep oceans.. But wherever on the surface of the earth ani- mals or plants are found, there, in the earth, the air, and all bodies of water, are also found bacteria. Air. Bacteria are so extremely minute that they are capable of floating in the air for a long time and of being blown by the winds almost indefinitely. Consequently it is almost impossible, at least in inhabited localities, to find any air that does not contain them. The number that may be present in the air varies with the density of human population. We find them more abundant in city than in country air; more abundant, as a rule, in houses than out of doors; more abundant in the air of rooms well filled with people than in empty rooms, since they DISTRIBUTION OF BACTERIA 1I5 arise from clothes and skin. In the air of schoolrooms or audience rooms the number of bacteria is very great, and there are more at the close of a school session than at the beginning. There are more bacteria in the air of a poorly ventilated schoolroom than in the air of a sewer. The presence of animals as well as of men always increases the number of bacteria in the air, Wherever we find dust, there we find bacteria. By this it is not meant that dust is composed wholly of bacteria, for many other things go to constitute what we know as oo% zie ae Vite dust; but among the dust 44 b € particles we may be sure to é ed, Me a> Cae d AL. find bacteria in great num- ilS/ ed bers. In short, all airin the “> ra pr vicinity of habitation contains ind ‘ : é Fic. 55. A group of bacteria in bacteria. The air of high venlee: mountains far from the habi- a, Bacillus ubiquitus; 6, bacillus circu: tation of animals is found fans; c, bacillus superficialis; d, ba- cillus rubescens; e, bacillus hyalinus ; to be moderately free from S, bacillus delicatulus ; g, bacillus jan- these ubiquitous organisms. 9“ Elsewhere they are present in abundance. Since this is the case it is quite impossible for any material exposed to the air for even a short time to escape a rapid contami- nation with microdrganisms. Water. Practically all bodies of water on the surface of the earth are filled with bacteria (Fig. 55). The number found in water, however, is widely variable. In spring water which comes fresh from the ground the number is small, and in some cases they may be wholly absent. The same thing is true of the water of arteszan 116 BACTERIA, YEASTS, AND MOLDS wells, drawn from a depth of a hundred feet or more. All surface waters are sure to contain them, for they are present in lakes, ponds, pools, rivers, and in the ocean. They are more abundant in flowing streams than in water standing in lakes or reservoirs, quite contrary to the usual belief. We commonly look upon running waters as purer than standing waters, but, so far as concerns bacteria, the severse is usually the case. Rivers or brooks contain them in large numbers; lakes in which the water has stood for a long time contain a far smaller quantity. The reason is that rivers and brooks collect the bacteria from the surface of the ground, from sewage, etc., and the longer they flow the greater the number of bacteria they con- tain, since they are great draining agents for the country. When water stands in lakes or ponds the bacteria, which are slightly heavier than the water, have a chance to settle to the bottom. This they do in the course of a few days, and after a time the water in such standing reservoirs becomes far purer than in the supply streams. It will easily be understood that the greater the amount of decaying matter entering any stream the larger will be the number of bacteria in its waters. The rivers of civi- lized countries, that receive the sewage from cities, not only contain these little organisms in immense numbers, but contain some of the most dangerous kinds, since they are the disease germs discharged from human patients. From these general facts we reach the conclusion that no water at our command upon the surface of the earth is absolutely free from bacteria. Spring water is the purest, and water from deep artesian wells is about equally pure. Water from lakes and reservoirs is the next in purity, and BACTERIA IN THE SOIL 117 water derived directly from flowing streams and rivers is most likely to contain these organisms in greatest num- bers. The most dangerous water for drinking pur- poses is that of rivers which have been contaminated in any way by sewage material, a condition of things true of the water used in some cities. Soil. Soil on the surface of the earth is usually filled with bacteria (Fig. 56). They are usually abundant in the superficial layers, decreasing rapidly as we pass below the sur- face, until at the depth of a com- paratively few feet they practi-° cally disappear. They are more abundant in some kinds of soil than in others. Where the soil is dry and sandy the number is comparatively small; where it is moist and loamy they are more abundant. They are found pro- fusely around buried bodies of Fic. 56. A group of soil animals, or in soil that contains baste: decaying roots of ordinary plants, “,*) Sut onznsm iB be mine They are immensely numerous — fusiformis; ¢, B. subtilis; f, Clos- . Ea ae terium pasteuriana. in the vicinity of earth closets or privies, and the soil near sink drains and manure heaps is filled with them. Indeed, any soil which contains the remains of animal or vegetable matter and a considerable amount of moisture will have bacteria in inconceivable num- bers, while in cleaner soils they will be much less abundant. They are sure to be abundant in all dirt which accu- mulates in a household, for nearly all such dirt contains 118 BACTERIA, YEASTS, AND MOLDS organic material in a state of partial decay. Any dirt which collects in corners of rooms, in the cracks of floors, or upon shelves in pantries, cellars, etc., is sure to contain bacteria in great quantities, The dirt that clings to the walls and ceilings of rooms is also quite sure to contain Fic. 57. A bit of decaying meat highly magnified, show- ing the bacteria feeding upon the material. them, and the dirt collected by sweeping the floors is filled with them. Bacteria in Food. Bacteria are found in all moist foods, especially in those undergoing the process commonly spoken of as spoiling (Fig. 57). Indeed it is the bac- teria, as we shall presently see, that ordinarily cause this spoiling. Any meat which develops the gamy flavor BACTERIA IN FOOD 119 is filled with them; sour mz/k contains them in immense numbers ; moldy bread and bad eggs hold millions of them, and decaying fruit may show bacteria as well as molds. All types of food which develop peculiar taints and tastes characteristic of putrefaction contain great numbers of bacteria. Long before these taints are appreciable to the senses the bacteria that produce them are abundant. No moist food can be exposed on pantry shelves or in ice chests, even for an hour, without containing bacteria, and after it has remained there for a day or two the number of bac- teria present in it becomes very great indeed, because of the multi- plication of those that have found entrance. In the Body. The presence of bacteria in food leads us to expect Fic. 58. Bacteria from the to find them in our mouths, stom- ‘eet? of healthy mouth. achs, and intestines. Our whole digestive tract is crowded with ‘them. Fig. 58 represents a bit of the scrapings from the teeth, highly magnified, and containing hundreds of several different species of bacteria. They are equally or more abundant in the stomach and intestines. This is the normal condition of things, and these bacteria do us no injury, but are probably of direct use. The substance of the matter is that bacteria are practi- cally everywhere on the surface of the earth. They are in immense numbers in the household, on the walls and ceilings of our rooms, upon our pantry shelves; they are present in every bit of food which remains exposed to the air for a short time; they are in all liquid foods, 120 BACTERIA, YEASTS, AND MOLDS particularly milk. So ubiquitous are they that it is an abso- lute impossibility for the housewife, by any means at her command, to keep her pantry and food free from them. These facts forcibly emphasize the futility of the common method of sweeping and dusting rooms. Bacteria are heavier than the air and, if undisturbed, settle and lie quictly upon floors, tables, etc. Every sweeping the room reccives stirs them up. A dustbrush sends them flying through the room, only to settle down again later. On the other hand, wiping Fic. 59. Vetri dishes exposed, one, a, before, and the other, 4, after a class has occupied a schoolroom. with damp cloths removes the bacteria and this is a proper method of cleaning. This is especially true for kitchens and pantries where food is exposed to the air, and for school- rooms where there is likely to be a collectidn of numerous kinds of bacteria, including some disease germs brought by the many children. Fig. 59 shows two plates, one exposed to the air before and the other after a school session. The relative abundance of bacteria floating in the air is clearly shown. These facts forcibly show the advantage of vacuum cleaners, which remove the dirt without stirring up the dust. RESULTS OF BACTERIA GROWTH 121 These facts, too, show the desirability of having the walls of kitchens and pantries smooth and glazed, in order that they may not furnish lodging places for air bacteria and may be cleaned readily with a damp cloth. They also show us that lace curtains and heavy hangings around rooms will be lurking places for numerous organisms. This may do no harm in ordinary parlors, rooms where the bacteria are mostly harmless and where no food is kept, but should never be allowed in kitchens, and should be most’ emphatically forbidden in sick rooms where dis- ease germs are likely to be floating about in the air. THE RESULTS OF BACTERIA GROWTH The bacteria with which we are concerned all require complex foods. Some species can live upon simple min- erals from the soil, but these are of no importance in the ‘household. All that are of interest for our purposes feed upon substances quite similar, in general, to those upon which animals subsist. Any materials containing sugars, starches, protetds (albumen, lean meat, etc.), or other ani- mal foods, furnish excellent nourishment for bacteria. For this reason the bacteria are in a sense the rivals of the animal kingdom. Both animals and bacteria feed upon the same kind of food, and both are, therefore, constantly seeking to obtain and use it for their own purposes. When we bear in mind the facts thus far outlined we can easily understand why bacteria play such an important part in the affairs of everyday life. They are too small to see, but are capable of inconceivably rapid multiplication. They are all about us in great numbers, in earth, air, and 122 BACTERIA, YEASTS, AND MOLDS water. Some can be dried without injury, others frozen for months without losing their vitality, and even a short boiling fails to kill many species. With all these wonder- ful properties it is not strange that they are constantly at work all around us modifying the nature of all substances upon which they feed. PARASITES AND SAPROPHYTES The food upon which bacteria feed may be either living or dead. If bacteria are capable of feeding upon the living body of an animal or plant, we call them parasites. Such bacteria quite naturally produce injury to the life of the individual upon which they feed. In mankind they produce a great variety of abnormal results which we call diseases. The parasitic bacteria, therefore, are commonly called disease germs, and are the cause of most of our con- tagious diseases. Many of them feed upon animals, pro- ducing animal diseases, while others live upon plants, giving rise to diseases in the plant world. Fortunately only a comparatively small number of spe- cies of bacteria are capable of existing upon living bodies of animals. The great majority are incapable of feeding upon living tissue, although they feed upon it readily enough after it is dead. Those dependent upon the dead bodies of animals or plants cannot live a parasitic life. When bacteria feed upon such nonliving materials we call them saprophytes. They are, like animals in general, depend- ent for sustenance upon dead animal and vegetable food The saprophytic bacteria, while they may be rivals of ani- mals for food, are not the cause of diseases. These harmless SAPROPHYTES AND PARASITES 123 bacteria far outnumber the disease germs. We should not therefore be frightened when we learn that bacteria are all around us, in the food we eat, the water we drink, and the air we breathe. Most of them are harmless or beneficial, and need cause us no uneasiness. It should also be noted, finally, that some bacteria can live both upon living tissues, like parasites, and upon dead material, like saprophytes. Such microorganisms are partly parasitic and hence are capable of producing disease. They are also capable of living outside the body in various localities in nature. They may be of serious importance to the health of man, inasmuch as they are capable of living a parasitic life if they can get into the living body; but are also able to live an independent life in nature. All disease bacteria either belong to this class or are strict parasites, while the harmless bacteria belong to the class of saprophytes. CHAPTER IX BACTERIA WHICH LIVE UPON DEAD FOOD: SAPROPHYTES These include the bacteria found living freely in nature, in the air, in water, and in the soil. Since they live upon dead organic material they may be expected in any kind of food upon which the human being lives, as well as in other substances that do not serve us as food. MATERIALS THAT SERVE BACTERIA AS Foop Some kinds of food are very readily attacked by bac- teria, others with more difficulty, and some hardly at all. Pure sugars are, as a rule, not attacked by them, although if the sugar is in water solution certain bacteria may some- times feed upon it, and raw sugar is sometimes injured by bacterial growth. The same is true of pure starches, since most bacteria are quite incapable of making use of pure starch. It happens, however, that nearly all of our food materials containing starch and sugar contain also other substances upon which bacteria can feed, so that the sugary and starchy foods in our households are by no means exempt from them. azs are also attacked by bac- teria, although less readily than some foods. By bacterial action the fat is made rancid and undergoes other less familiar changes. 124 FOODS OF BACTERIA 125 The food most readily attacked by the majority of bac- teria is the class known as profeids. Proteid materials are foods for nearly all species of bacteria, are most easily attacked by them, and are sure to be consumed if exposed to the air under proper conditions. By proteid food is meant a class of chemical substances, highly complex in nature, which may best be understood by illustrations. The best known examples are the following: the white of egg, named albumen; the lean part of meat, known by chemists as myosin; the curd of milk, called casein ; gluten, which is the gummy substance present in wheat flour; a similar substance present in beans, known as legumen. All of these substances will be recognized as liable to putrefy rapidly. Nearly all of our foods contain either these proteids or others in greater or less abun- dance. Anything made of flour contains gluten ; any- thing that has milk in it contains casein; all meats contain myosin ; anything made of beans or peas contains the legumen, while eggs always furnish albumen. Since most foods contain some of these substances, and since cooking does not change their nature, practically all foods hold some of these proteids. Proteids are of all foods the most necessary for the human body. While the body might live on proteids alone, it could not live entirely on any other kind of food, and proteids therefore are absolutely necessary for the human body. Most bacteria flourish upon proteids as well as we do, and inasmuch as practically all of our food products contain a certain quantity of proteids, it follows that nearly all of our foods are readily consumed by the great host of saprophytic bacteria. 126 BACTERIA, YEASTS, AND MOLDS Tue Errect or BacTERIAL GROWTH UPON Foop If any common food product is sufficiently moist, bac- teria which get into it from some source are sure to grow and in the course of a few hours will produce marked changes therein. But bacteria do not consume food as large animals do by taking it bodily inside of themselves. They are quite too small todo this. To the eye it does not seem that the bacteria are actually consuming the food but that they are simply producing noticeable changes within it. In reality, however, they are consuming it and in the end cause its almost complete disappearance. The essential effect that they produce is the chemical decomposition of the material upon which they are feed- ing. Bacteria do not consume the whole food but use only a part of it. An illustration may make clear their mode of action. If a house is built with a wooden frame and brick walls, and the wood is burned away, the house is sure to tumble to pieces, because the wooden framework is necessary to hold the building together. Much the same thing is true of a chemical molecule, which is a structure made of a variety of substances bound together to form a unit. Bacteria, as they utilize foods, have the power of taking some of these materials out of the molecule, but cannot consume the whole. The result of extracting some of the material from a molecule is that the entire structure will fall to pieces, just as the house falls whose framework has been burned away. The meat becomes putrid, the milk sours, the egg rots, and any other material containing proteid undergoes a similar type of spoiling. PRODUCTS OF BACTERIAL GROWTH 127 New Propucts Decomposition Products. When a house falls to pieces after burning, a mass of débris is left lying in the old cellar. So, when the chemical molecule is broken to pieces, as described above, there will remain certain fragments of the original molecule. Although really fragments of the original substances they are quite different in nature from the original material.. They are known as by-products of decomposition, or simply as decomposition products. When- ever bacteria grow in a mass of food, destroying the chemical nature of the food molecules, there is sure to be produced a variety of materials representing the débris from the destruction of the molecule. These materials are by-products of decomposition and are always of a nature quite different from the original food substance. They are, as a rule, simpler in their chemical nature than the original food, and are quite different in their physical characters. From the original food, which may have been a partly solid material, like a bit of meat, there arises as the result of its destruction a number of these by-products, some of which are in the form of gases and pass off into the air, some of which are more or less liquid and remain behind in the food mass. Others are easily soluble in water and dissolve in the liquids of the food. Thus the food material is almost sure to soften gradually and to become of a more or less fluid nature. There is likely to be a considerable variety of these by-products, some of them having new odors and tastes. The new materials give to the food mass as it is consumed by bacteria wholly new flavors ; 128 BACTERIA, YEASTS, AND MOLDS and since some of them are vapors they may give it a strong odor. Consequently the food material which is being consumed by bacteria soon begins to have a very strong taste and odor, due to some of these decomposition products. The character of the food changes very greatly, and after the bacteria have had an opportunity of feeding upon the material for a comparatively few hours no resem- blance to the original food mass remains, in appearance, taste, or smell. This whole phenomenon is spoken of as putrefaction, or decay. There is, however, a slight difference between these two terms. By putrefaction we commonly mean a change in food masses by which a series of very unpleas- ant odors and tastes make their appearance in the putre- fying mass. By the term “decay” we properly mean a more complete destruction of the food material, in which the unpleasant odors and flavors finally disappear, leaving behind a comparatively odorless material which represents the final débris remaining from the total destruction of the food masses. Putrefaction, with its high flavors and odors, is an incomplete process; decay, a more complete process of destruction. Putrefaction is produced in gen- eral by bacteria when they do not have an abundance of air or oxygen, whereas decay occurs when the amount of air or oxygen present is abundant. In other words, when a bit of food is being consumed by bacteria without suffi- cient oxygen it putrefies and becomes offensive in taste and smell; when, however, the oxygen is abundant, the pro- cess of putrefaction goes on to a more complete destruc- tion, ending finally in what is known as decay, by which the material is converted into inoffensive substances. BACTERIAL SECRETIONS 129 Bacterial Secretions. Besides the decomposition prod- ucts just referred to, another class of new substances is found in the putrefying and decaying food, and these are to be regarded as secretions from the bacteria, Bacteria are living organisms and, like larger animals and plants, are con- stantly emitting from their bodies certain secretions. Our own bodies are constantly secreting materials, like perspira- tion, urea, etc.; and bacteria, as the result of their activity, are also constantly producing a small amount of secretions. These secretions are totally different products from the original food. The secretions from some species of bac- teria are quite harmless, although others are of an intensely poisonous nature. As a result, a bit of food that is under- going putrefaction may in the course of time become highly poisonous because of the appearance of poisonous materials, part of which may be decomposition products but most of which are probably bacterial secretions. Chemists and bacteriologists are not able to separate very clearly decomposition products from the secretions of bacteria, and for our purpose it is quite unnecessary. We need only remember that as the bacteria consume our food products they produce profound chemical changes which we call putrefaction and decay. As the result of these changes not only is a host of highly flavored prod- ucts developed but also another series with strong odors. Some of these new products are poisonous, others are not. All of them have a tendency to be softer than the original food and more easily dissolved in water; the result of which is that as the food is consumed by the bacteria it becomes softer and more liquid. In the end it largely disappears, being dissolved into gases which pass off into the air and 130 BACTERIA, YEASTS, AND MOLDS liquids that soak down into the soil or evaporate, leaving only a small residue. This is the general phenomenon of putrefaction, ending in complete decay. Advantages from Incipient Decay. Although this pro- cess of decay may be a somewhat rapid one, it actually takes place by steps, one after another. The breaking down of the food under the action of bacteria is not a sudden falling of the molecules into fragments but a pro- cess that takes considerable time and presents a number of intermediate steps between the original food and the final condition of decay. As the bacteria begin to act upon the food it is not at first necessarily ruined or even injured, At the beginning of the process the new prod- ucts are quite different from those that appear later, and it may happen that those first produced give to the food a slight favor which, instead of injuring its character, actually improves it. The presence of a certain amount of flavor in our foods is very desirable, and even necessary. Pure foods with- out flavors cannot be properly digested and absorbed, a certain amount of flavor being needed to stimulate the digestive organs. Some of the flavors arising in the early stage of decomposition are of a character that is enjoyed by the human palate. For example, the so-called gamy taste of meat is a flavor which some people enjoy very much, while others dislike it. This gamy taste is simply the beginning of decomposition, and is due to the fact that the meats have been kept until the bacteria have begun to act upon them and to produce the incipient stages of putrefaction. In this early period the flavors are not very strong and not particularly unpleasant; but FLAVORS FROM INCIPIENT DECAY 131 if the process is allowed to go a little farther the taste of putrefaction becomes too strong for any palate. Another example is Limburger cheese, in which a strong flavor of incipient putrefaction is produced by the development of bacteria in the cheese mass. Any one who has ever known the flavor or taste of Limburger cheese will easily believe that it is incipient putrefaction. Other forms of soft cheeses show the same feature in less degree. A great variety of flavors and odors is found in the so-called soft cheeses, nearly every one of which represents a certain type of incipient pu- ee trefaction. Even the hard cheeses show S@ Xe this same characteristic, though there is re a less similarity to putrefaction. Neverthe- less the taste of the hard cheese is prob- F!G. 60. Bacterium ably, at least in part, due to the beginning Ailsa: ea of this process of chemical destruction produced by bacteria. If the cheese has become over- ripened, a very strong decayed taste may be apparent. In the making of butter the same phenomenon occurs, for the extremely delicate flavor of a high quality of butter is due to the action of bacteria upon the cream before the butter is made, and the butter flavor is thus one of incipient decay (Fig. 60). It is one of the most exquisitely delicate of all our food flavors, and is highly enjoyed by all people. VINEGAR Another example of a benefit derived from bacterial action is in the manufacture of vinegar. This is a mate- rial which, though not a real food, is used in considerable 132 BACTERIA, YEASTS, AND MOLDS quantities as a condiment and preservative. As ordinarily made it is simply a product of bacterial growth. The basis of vinegar is acezze aczd, and this is produced from alcohol by certain changes brought about in it through the action of microérganisms. The source of vinegar is always some weak alcoholic solution, commonly cider or weak wine; but any liquid that contains a moderate quantity of alcohol may be a source of vinegar. This material is caused to undergo a chemical change which converts the alcohol into acetic acid, and when this occurs it becomes vinegar. The change of the alcohol into acetic acid is brought about by the presence of a material, a brownish, felted, slimy mass, which increases in amount as the vinegar is made, and upon whose presence the conversion of alcohol into vinegar seems to depend. This has long been known as mother of vinegar. Good vinegar will always contain such mother. The study of this mother of vinegar shows it to be a mass of bacteria (Fig. 61). They are crowded together in countless millions to form this slimy mass, and during the production of the vinegar multiply rapidly and finally become excessively numerous. The grvow¢h of the bacteria produces the change in the alcohol which con- verts it into acetic acid. The formation of common vinegar is therefore due to the development of microdrganisms. Some types of a cheap product are made by a chemical process, but all good table vinegar is produced by bacteria. A knowledge of the manufacture of vinegar is to-day a matter of little importance in the household, for the mate- rial is commonly made either in large factories or in a farmer’s cellar. Tne housewife is simply concerned in VINEGAR 133 purchasing a good product, and in its use. The type of vinegar commonly regarded as the best is that which is made from cider, although a large part of the vinegar used in the world is made from some other source of alcohol (wine, beer, etc.). The value of vinegar is in a measure Nes dependent upon its flavor, JO BEL | eee Se 52. which differs according to | ez the material from which it is made. Vinegar, of course, has always an in- tensely sour taste from the presence of acetic acid, but in addition to this there are other flavors, due to the original material from which it is produced, and these affect its value. Vinegar also varies in color according to the substance from which it is made. Cider vinegar is of a rich brown color, while if made from other materials it may have a reddish or whitish color, or may be almost black. The color, therefore, is no indication of the char- acter of the vinegar, for a perfectly good product may be white, red, or brown. The market value of vinegar is dependent chiefly upon the amount of acid it contains. The higher the percentage of acid (the sourer it is), other things being equal, the greater its value. Fic. 61. Bacteria producing vinegar. 134 BACTERIA, YEASTS, AND MOLDS Although they are not bacteria a word may be said in regard to the vznegar eels frequently found in good cider vinegar. These are minute little worms, just visible to the naked eye, which are frequently seen swimming near the surface. Their presence may be consistent with a good quality of vinegar. They do not themselves have much influence upon vinegar, although if abundant they weaken its strength. They are quite harmless to the person using the vinegar, and one need never be suspicious or throw away any because it contains large numbers of these eels. They must be looked upon as present in ordinary good cider vinegar, and must be classed among the perfectly harmless organisms which are sure to occur in some of our food products, Foop EVENTUALLY RUINED BY BACTERIA These illustrations are sufficient to show that the by- products of decomposition are not always necessarily dis- advantageous to our foods. If the chemical destruction is only beginning, the result may be of a pleasant nature, and the food may be actually benefited by the action of the bacteria. If, however, this process is allowed to go farther, most foods are entirely ruined. Gamy food soon becomes putrescent; soft cheeses of all kinds soon undergo putrefaction and decay, and even the hard cheese in the end will become ruined by. the development of too strong a flavor of putrefaction. Butter in the course of time is also ruined, although bacteria do not grow readily in butter and it may be kept a long time without undergoing putre- faction. It is, however, really impossible to draw any GARBAGE 135 fine between the incipient decomposition that benefits the flavor of food and the later stages which utterly destroy it. Although the flavors of incipient decomposition may be pleasant and useful, the taste produced by later stages is offensive. In the end the food is always totally ruined, for bacteria will finally produce the complete destruction of the materials upon which they feed. The kinds of putrefaction, that is, the odors and tastes that develop, are by no means always the same. Different species of bac- teria produce different results, and the same species of bacteria produces a quite different kind of decay in differ- ent sorts of food material. But it is a matter of little significance what type of putrefaction occurs, for. all of them are equally sure to destroy the food. It is useful to remember, however, that the kind of decomposition which is produced when bacteria grow without sufficient air is always more unpleasant and more dangerous than that which takes place where there is plenty of air. Any food material which is closed in tight bottles or jars and under- goes putrefaction is sure to give rise to more unpleasant odors and tastes and to decidedly more unpleasant types of decomposition than food material which decays in the open air. GARBAGE All the refuse from our tables or our kitchens is just as good food for bacteria as is the material which we actually consume, and all of this waste material, after we have discarded it, is attacked by bacteria. This is shown simply enough by the odors arising from garbage if it is 136 BACTERIA, YEASTS, AND MOLDS allowed to stand, the putrefaction and decay that set in being sure indications of the presence of bacteria and proofs that the bacteria are decomposing the material. Such waste material is, of course, of no use in the house- hold, since it is not in a condition to attract the palate of man; but there is a large amount of food material left in these waste products which is very useful for feeding certain animals. It has commonly been used for feeding hens and hogs, and the recognition of its food value has in recent years made the garbage of our large cities a very valuable product. This use of garbage is being abandoned as unhealthful, and the practice of burning the material is becoming common. The housewife is not, however, concerned in this prob- lem but only in the proper disposal of the waste material from her kitchen and her table. This she simply desires to get rid of, and its tendency to rapid putrefaction makes it imperative that it be disposed of at once and not allowed to accumulate. She can adopt a variety of methods for this purpose. She may burn it, provided it is not too large in quantity, is not too moist, and she has a fire hot enough for the purpose. As a rule, however, burning garbage in an ordinary kitchen stove is not very feasible. It is commonly too moist to be easily consumed in a moderate fire; but where possible this is the best means of getting rid of the waste. The usual method of disposing of garbage in a city is to allow it to be removed by those who pay for the privi- lege because of the value of the material for feeding hogs. The household waste is placed in receptacles, which are emptied by the garbage collectors. In order that such GARBAGE 137 receptacles may be kept in a tolerably wholesome con- dition, the garbage should be removed frequently, and for this we must depend upon the faithfulness of the col- lectors. The vessels themselves should occasionally be cleaned. If not cleaned, they give rise to unpleasant, unwholesome odors in or around the house. They may become the breeding places for flies and prove to be in general a considerable nuisance. The chief trouble with such garbage cans is their smell and unsightliness, but these difficulties are removed if the cans are kept clean. It is not difficult to clean them. Cold water for washing garbage cans is of very little use; but if they are thoroughly washed with very hot water they can be kept so clean that they emit no odor and are not unpleas- ant. Since putrefaction is due to bacterial growth it is of course possible to prevent the smell and decay of the gar- bage by the use of disinfectants. Borax might be used for the purpose, but it is expensive ; and the use of more vigor- ous disinfectants is likely to make the material poisonous to hogs subsequently fed upon it, or to dogs who very fre- quently feed upon the contents of the garbage receptacle. Such disinfectants are quite unnecessary, and the only thing that the housewife needs to do is to keep the garbage can tolerably clean, and to see that it is emptied as fre- quently as possible. She should remember, however, that she cannot depend upon the garbage man to clean the recep- tacle. He will simply empty it. If the garbage can gets to smelling offensively, a thorough washing with hot water and sal soda applied vigorously with an old broom will make a great improvement. Naturally greater attention must be given to the matter in the summer than in the winter. 138 BACTERIA, YEASTS, AND MOLDS Closely associated with these problems are certain other minor questions relating to the kitchen sink. In the ordinary sink a considerable amount of organic material is liable to find its way into the drain and trap. The cloths used for washing dishes are also quite sure to become soiled with various forms of organic material from the food. These materials are liable to bacterial action and therefore will decay and become offensive. Consequently boiling water should be occasionally poured down the sink drain to disinfect the trap as far as possible, and the cloths used in dishwashing should be thoroughly washed in boiling water and dried to prevent them from becoming offensive by furnishing a chance for bacterial growth. CHAPTER X THE PRESERVATION OF FOOD: DRYING; COOLING The growth of bacteria in food is nearly always unde. sirable and the housewife must always aim to prevent it. Even where the incipient decomposition products are useful because pleasant to taste, this taste is developed in the food before it is received into the house, so that the housewife is not concerned in the methods adopted to produce the flavors. Her sole aim must be to prevent the food from spoiling. To do this she must constantly bear in mind that putrefaction is always due to the growth of microérganisms, and that all types of putrefaction and decay may be prevented by stopping the growth of such organisms, and delayed by decreasing its rapidity. Any- thing which will check the activity of bacterial growth will delay the spoiling of food products. In order to know how to treat food for this purpose it is most useful to bear in mind the facts already mentioned in regard to the growth of bacteria. To the housewife of to-day the problem of food preser- vation is of less significance than it was fifty years ago. To-day, at least in all communities of even moderate size, these problems have been largely solved for her by the marketman, and she can buy her food in such small quan- tities that frequently she does not need to consider the problem of preservation. The housekeeper of fifty years 139 140 BACTERIA, YEASTS, AND MOLDS ago was confronted with many problems in the preserva. tion of meats, vegetables, and fruits, because she was likely to have large quantities brought to her hands at once for immediate disposal. But though the questions are not so pressing in the modern home, they are still con- stantly arising in the well-regulated house. A somewhat extended notice of the subject is therefore necessary. The Use of Foods while Fresh. The first thing that must always be borne in mind is that nearly all kinds of food are better when used as fresh as possible. The earlier food is consumed after it reaches the household, the surer it is to be free from the troublesome action of bacteria and the more certain it is not to develop decom- position tastes and flavors. The necessity of using food while fresh is much more imperative with some foods than with others. Meats are especially liable to spoil, the meat of immature animals more quickly than that of adult animals, and must be used promptly. Many fruits, like cherries, berries, peaches, and pears, keep only a short time, and beans and peas spoil very quickly if kept moist. The endeavor should always be to use such materials at once. The housewife in our modern community should remem- ber that a small proportion of the food she buys is really fresh. The crowding of people together into cities de- mands a food supply coming from long distances, and the constantly open markets twelve months in the year require some food to be preserved for weeks and months before use. Hence our markets are filled and our tables loaded with various forms of preserved foods ; and whether she buys canned or salted goods, or meats or poultry, the PRESERVATION BY DRYING 14! housewife may be confident that some device for preser- vation has likely been used in their preparation. The modern city is possible only because we have learned methods of food preservation. It is of course not always possible to use all kinds of food in a fresh condition, and it becomes quite necessary to have some means devised for their preservation. The means adopted for preservation are always to subject the food to conditions unfavorable for bacteria growth. DryiInG Since bacteria require a considerable quantity of water for their growth and multiplication, they will not develop at all in foods that are even moderately dry. Molds will grow upon a food that has only a small amount of water, but bacteria require from 25% to 30% of water in their foods in order that they may grow. Molds will grow upon damp floors, damp cloth, or paper, but bacteria can attack these materials only when soaked with water. A practical application of this fact is dryzng,—one of the most widely used methods of preserving food. This is adopted by nature for the purpose of preserving many food products, like corn, wheat, oats, rye, etc. Nature wants to keep such seeds from decaying for some time, perhaps during the winter season, in order that they may be in good condition for the growth of the young seedlings in the spring. To accomplish this the seed, when it ripens, is deprived of its moisture, so that when fully ripe and ready to be shed from the -plant it has become a dry, hard, tough mass, forming the grain of wheat or corn, or 142 BACTERIA, YEASTS, AND MOLDS the dry pea or bean. Such a food material is beyond the reach of bacterial action, and, unless these grains become subsequently soaked with water, they are protected from decay (Fig. 62). Bacteria grow in them readily enough in the spring when they are moistened and begin to sprout. This drying of the grains protects all kinds of flours and meals made from them. The wheat is ground into flour, and the corn into meal, each of which con- tains but a small amount of moisture, far too little to allow bacteria to feed upon the material. Flour is perfectly good food for bacteria, and if we only moisten it with Fic. 62. Showing nature’s method of . preserving seeds by drying. The upper Water, putrefaction and figures are the fresh seed, the lower decay begin in a short figures the same after drying for winter Poole time; but as it is ordinarily prepared the amount of moisture is too slight for bacteria. The same is true of all flours or meals prepared by grinding dried seeds furnished by plants. Toa less extent the same is true of various food preparations made from these flours. In making bread or cake dried flour is mixed with water and subsequently baked. The mixing of the flour with water brings it into a condition for bacterial action, but the baking dries up enough of the water to preserve it. If the baking is so thorough that the water is almost completely driven off, as in the case of dried biscuits, or crackers as they are called in the United States, the PRESERVATION BY DRYING 143 material is left so completely dry that bacteria cannot consume it at all. Dried crackers, if kept dry, can be pre- served indefinitely, neither decaying nor molding. In the case of bread and soft cakes the water is not wholly driven off; hence these foods are not protected entirely from -the action of microdrganisms. As a rule bacteria cannot attack them and the housewife hardly fears their decay ; but molds can grow upon them readily, and they must therefore be protected by means already suggested. In addition to foods that are naturally dry, a large variety of others may be preserved completely from bac- terial action by artificial drying. This method of pre- serving has been known for centuries and is understood by both civilized people and savages. Most kinds of meat can be treated in this way, and the drying of meat is carried on to a large extent in different parts of the worid. The frontiersman and the hunter in the woods sometimes cut the flesh of deer, bears, and other animals into thin strips and hang it where it will be dried by the heat of the sun. This dried meat is called pemmican, a tough, hard, dry substance which can be kept for months without danger of decay. It is good food, though somewhat less digestible than fresh meat. A similar drying could be adopted in the household to preserve meats, but it is rarely worth while. Usually the efficacy of the drying is increased by the use of salt. This plan for the preservation of meat is adopted in many parts of the world where cattle are plenty and the market is distant. In South America thousands of tons of dried flesh are prepared each year, the drying in this case being produced artificially, and the meat being 144 BACTERIA, YEASTS, AND MOLDS still further protected from: decay by the addition of a small quantity of salt. Such preserved meats are then shipped all over the world and form an excellent food which can be kept indefinitely. The commercial names under which this dried meat is sold are several; the more common ones are chargue and tassajo. Such meats, though useful, do not take the place of the fresh product. Their flavor is changed; they are tough and not easy to digest. A more familiar method of preserving meat is the cur- ing of hams, bacon, etc. In such cases the flesh is first salted thoroughly by soaking in a brine, and then sub- jected to the action of smoke from burning wood. Such smoked food is thoroughly protected from bacterial action by at least three factors: (1) The material becomes some- what dry, so that the bacteria cannot readily act upon it. (2) The action of the smoke is in a measure antiseptic, partly destroying bacterial life upon the surface, and at the same time so impregnating the meat with injurious vola- tile products that bacteria cannot ordinarily grow in it. (3) The salt is itself injurious to bacterial life. The ham is thus preserved from the action of bacteria by a combina- tion of drying, smoking, and salting, all of which processes together are sufficient to prevent completely the subse- quent growth of bacteria, although molds may grow upon it if it is not properly protected. The same thing is true of dried beef, a material preserved from decay partly by a pre- liminary soaking in brine and partly by a subsequent drying. The methods of preparing dried beef vary. Sometimes the process is one of artificial drying simply, but commonly smoking and salting are adopted to aid in the process. The drying of flesh is sometimes carried out so completely that PRESERVATION BY DRYING 145 the mass can be reduced to a powder. Powdered meat, however, is an article of commerce not very widely used. Drying is adopted extensively for a variety of other animal foods. It is much used in preserving fish, some- times without salting, sometimes with an abundance of salt. The heat of the sun, artificial heat, and smoking are all employed. Mzssels and other shelifish are some- times preserved by drying. One of the most recent and useful applications of dry- ing is in evaporating m/z. Milk is now easily dried by special devices and is put upon the market at a low price. The dried product will keep indefinitely, and is an extremely valuable food, since it is one of the cheapest as well as the most nutritious that can be bought. It will not take the place of fresh milk, for when subsequently dissolved in water it has a peculiar flavor, not unpleasant, but not like milk. For baking and for many other purposes, how- ever, it has proved to be one of the most useful as well as one of the cheapest of foods. It is as nutritious as milk, is easily digested, and has the great advantage of keeping indefinitely without decaying, souring, or molding. In the drying of flesh, milk, etc., it must be remembered that the process simply checks the growth of bacteria, but does not necessarily kill them. Hence, if the meat con- tained any disease germs at the time of drying, the process itself would not remove the danger of eating it. Meat from diseased animals cannot, therefore, be rendered fit to eat by drying. Even the parasitic worm, 77ichina, can withstand the smoking in the curing of ham. Unless the temperature is raised quite high during the drying, the process does not, therefore, remove dangers attending 146 BACTERIA, YEASTS, AND MOLDS the use of food procured from diseased animals. In the process commonly adopted for drying milk, sufficient heat is used to render harmless any disease germs it may have originally possessed. A large variety of fruits, berries, and vegetables are also capable of preservation indefinitely by the simple process of drying. The farmer’s wife has long known that she can preserve apples by cutting them into small pieces and hartging them in strings over her kitchen fire todry. The same thing is possible for many vegetables, like squashes, pumpkins, and even potatoes. Many kinds of berries — blackberries, blueberries, strawberries, and some others —can be preserved by merely extracting from them a large part of their water. This drying of fruits and vege- tables is often accomplished by subjecting them to artificial heat, but more commonly in recent years the materials are subjected to hydraulic pressure, by means of which the water is actually squeezed out. A slight subsequent drying is then sufficient to preserve the material almost indefinitely. Some fruits are preserved by a combination of drying and the presence of considerable sugar. . Radsins, for example, are dried grapes, but they are not dried so com- pletely as berries, for some moisture is left in them. The preservation of the raisin from decay is due in part to the lack of water, but chiefly to the presence of a high per cent of sugar, which is in itself deleterious to bac- terial action. So, too, with other sweet fruits like prunes, apricots, figs, dates, curvants, etc. Their preservation is partly a matter of drying and partly the result of the sugar present. PRESERVATION BY DRYING 147 A large variety of fruits may be preserved by drying if we only have proper means for extracting the water. Indeed, probably any fruit could be thus preserved for future use if we could find a practical method of drying it. Todo this the fruit, divided into small pieces, must be subjected to a heat sufficient to dry it rapidly so as to prevent decay, but not sufficient to cook it. It is hardly worth while to attempt such work in the ordinary home, for the results are not entirely satisfactory, and dried fruits are easily purchased. Some such method is practical with certain fruits and impractical with others ; but it always greatly changes the nature of the fruit. Before it can be used the dried fruit must be soaked with water to soften it, after which it rarely bears much resemblance to the original fruit. Dried apples are quite different from fresh; the taste of the fresh apple has wholly disappeared, leaving in its place an entirely different flavor, The same is true of practically all fruits preserved by dry- ing. Their food value has not been reduced, for a bit of dried apple is just as nutritious as the fresh; but fruits have very little food value at any time, and are eaten mostly for their flavors. Dried fruit is much inferior in taste and cannot be used for so many purposes as fresh fruit. The drying of fruits and vegetables leaves a pulpy, somewhat tasteless substance, which, although it still retains its original food material, has lost the peculiar charm which gives value to the fresh fruit. It must be evident, then, that drying is the most widely adopted method of preserving foods, but it is not equally useful for all kinds. With some it works to perfection. For grains or other foods obtained from seeds it leaves 148 BACTERIA, YEASTS, AND MOLDS nothing to be desired. It is useful for meats and many other kinds of animal foods. For vegetables and fruits its value is far less, and sometimes very doubtful. For them it should be used only where there is a large quantity of fresh material for which no better method of preserva- tion can be found. Use oF Low TEMPERATURES The value of low temperatures in preserving all forms of food is familiar to every one. Microérganisms are stimulated into active growth by high temperatures and checked by low temperatures. It must be remembered, however, that the temperature at which bacteria grow most readily is not always the same; for although some species flourish only at warm temperatures, from 70° to 100°, others grow best at temperatures only a few degrees above freezing. While, then, a low temperature will check the development of most bacteria, it will not, unless it is actually below freezing, wholly prevent it, since some species grow readily enough at low temperatures. In the consideration of the use of low temperatures, therefore, three phases of the subject may be considered, based upon the degree of cold obtained. 1. Cold Storage. By cold storage is meant the use of storehouses which are cooled artificially, and where a very low and constant temperature is maintained for months at a time. In some compartments the temperature is held at a few degrees above freezing, while in others it is even below freezing. These low temperatures are commonly produced by the use of artificial-ice machines, COLD STORAGE - 149 based upon the vaporization of ammonia, and kept con- stant in spite of great changes in the temperature of the air outside. Cold-storage plants are a modern device, and only within comparatively recent years have they come to be used to any considerable extent for the pres- ervation of food. They are now found in all our large cities, and they are being utilized more and more each year, producing profound modifications of the conditions of civilized life. By means of them a large variety of foods can be preserved for many months without any tendency toward putrefaction and decay, and may be used at any time with the confidence that they have been kept in a perfectly good condition. The cold-storage plants make it possible to keep fresh for winter or spring use a large quantity of the perishable products which previously, if not capable of preservation by canning, it was necessary to throw away because of the certainty of putrefaction and decay. Such devices are producing a far more equitable condition in the food supply of modern communities. It is now possible to have fresh at any season of the year the perishable food products produced at almost any other season, provided we take the trouble to preserve them in cold-storage plants, and our city markets can furnish fresh fruits at almost any time. The length of time during which food can be preserved by cold storage depends upon the temperature. If actually frozen, as is commonly the case with fish, fowl, and flesh generally, food may be preserved indefinitely. Frozen food in the arctic regions keeps for years, and will indeed keep as long as it remains frozen. The same would be true of frozen food in cold storage. But some kinds of 150 BACTERIA, YEASTS, AND MOLDS food, particularly fruits, are ruined by freezing. In these cases the temperature may approach freezing but must never quite reach it. Such food will be preserved for a while, perhaps for months if the temperature is low, but not indefinitely. The cold-storage plant cannot be utilized by the house- wife, and need not therefore be further considered here. She should always remember, however, that during the winter and spring a considerable part of the perishable food products purchased in markets has come from cold- storage plants, where they have been retained for a long period at a temperature in the vicinity of freezing, or even below it. If she buys fish, fowl, or fruit during the win- ter, in a city market, she may regard it as probable that they have come from cold storage. This is a matter of considerable importance because of the practical question of the keeping property of such material. The question has frequently been raised whether foods from cold storage is not subject to exceptionally rapid decay after being brought again to a warm temperature. It is a general belief that meats and other materials that have been frozen decay very rapidly after they are thawed out, and hence that food taken from cold storage must be used quickly, since it will putrefy more rapidly than when fresh. This belief seems to be well founded, but the reason for it is not clear. Possibly the food is slightly changed in its physical nature by the freezing so that bacteria can more readily act upon it when it is thawed. In many cases, however, especially with fruits, which are not actually frozen, the rapid decay which follows re- moval from cold storage is due to the large amount of THE ICE CHEST ISI moisture which condenses upon the surface of the cold fruit when it is placed in warm or damp air. Such sur- face moisture, as we have seen, furnishes the necessary condition for the starting of mold growth. The prac- tical lesson to be learned is that after the material has been removed from the cold storage and warmed up to ordinary room temperatures it should be consumed as rapidly as possible, because putrefaction and decay are sure to take place speedily. If not used at once, it must be kept in an ice chest. There is practically as much difficulty in keeping food bought in the markets from decay in the winter, if kept in a warm house, as there is in the summer. Cold-storage plants are hardly found outside of large cities, and persons at a distance must depend upon other means of producing low temperatures. These are easy to obtain in winter, but difficult in summer. 2. Temperature of an Ice Chest. A far less efficient means of obtaining low temperature is by the use of the ordinary ice chest, —less efficient than cold storage simply because the temperature is higher. The temperature of ice chests is variable, depending upon the size of the chest and the amount of ice in it. It will sometimes be as low as 40°, or even lower, but never quite reaches the freezing point ; at other times it will run up to 50°, and as the ice’ melts the temperature rises to that of the outer air. Food preserved in an ice chest is far less thoroughly protected than in cold-storage plants. The use of the ice chest is simply a means of checking the development of bacteria, but it by no means stops their growth. At the tem- perature of 40° most bacteria, if they grow at all, grow 152 BACTERIA, YEASTS, AND MOLDS very slowly, and the food. may therefore be preserved for quite a long period, although it is sure in the end to undergo certain forms of putrefaction. The type of putrefaction that occurs in material kept in an ice chest is usually somewhat different from that which occurs in the same material at an ordinary room temperature. The common putrefactive bacteria grow readily at high temperatures, but hardly at all at the temperature of the ice chest. Other types of bacteria, however, grow more readily at the lower than at the higher temperatures, and meat or other food kept in the refrigerator will in the course of time undergo a type of decay due to the microdérganisms favored by the low temperature. This decayed meat appears somewhat dif- ferent from decayed meat at higher temperatures and has a different odor,—a fact indicating a different type of pu- trefaction. Certain peculiar kinds of decay are seen at these low temperatures which are hardly found under other conditions. Occasionally, for example, fleshy foods, particularly those from salt water, like lobsters or fish, develop a peculiar phosphorescence if kept in an ice chest. If examined in the dark they will be seen to glow with a somewhat brilliant greenish light. This phosphorescence is due to the development of certain very interesting kinds of bacteria, and always appears if they grow luxuriantly at low temperatures. They grow chiefly upon foods which contain considerable salt, and hence particularly in marine foods. They are more likely to be found in meat pre- served in an ice chest, since the more common decay produced by other bacteria will at higher temperatures mask the growth of the phosphorescent bacteria. It is THE ICE CHEST 153 not necessary to throw such food away, since the phos- phorescence does not appear to render it unwholesome, and it may be eaten with impunity. Although far less efficient than cold storage, the ice chest is a means of preserving for a short time food that would otherwise quickly spoil. Its efficiency depends upon its temperature. The larger the amount of ice in an ice chest the lower its temperature and the greater its efficiency. If the amount of ice is very small there will be such a rise in the temperature that food placed in the ice chest will spoil. In spite of its drawbacks the ice chest has become a necessity in the well-ordered household. It is frequently necessary to preserve foods for a few hours before they can be used, and in the warmer temperature of spring, summer, or autumn this is frequently impos- sible without the use of ice. In particular is this true of the preservation of milk, a topic which we shall notice by itself. In many parts of America the ice chest has become an almost universal aid in the housekeeping of families in moderate circumstances, and has greatly simplified prob- lems of home economics. To the poorer families, how- ever, it is hardly known. The home with an ice chest may purchase food to advantage in quantity and preserve it for a few days till used. The poorer families must rely upon their food being preserved by dealers in food sup- plies, and can therefore buy only such small quantities as can be used at once. To keep an ice chest in good condition it must be frequently cleaned. The inside is sure to be damp, and dirt is quite likely to collect in the cracks and corners. 154 BACTERIA, YEASTS, AND MOLDS This dirt will furnish a good place for the growth of such bacteria as thrive in low temperatures, and thus the ice chest in time becomes unfit for use. Food will not keep well under such conditions, becoming infected with bac- teria as well as affected by the odors given off from the decaying material. A frequent cleaning is necessary to keep the ice chest sweet and thus make it possible to preserve food properly. 3. Temperature of a Cool Cellar.—It sometimes hap- pens that the only place for storing the autumn products is a cool cellar. This is frequently the case on the farm, especially when considerable material is to be preserved. A cool cellar is of use in any home, for it makes possible the purchasing of fruits and vegetables in bulk during the fall, when they are cheap, and their preservation for use till a later season when they are more expensive. The value of a cool cellar rests upon two facts: (1) The temperature is usually /ower than in other parts of the house. (2) It is more likely to be wzzform. A cellar under- neath a house will have during the winter season, at least in cool climates, a temperature not much above freez- ing. For reasons which we have already considered such a temperature will preserve fruits and. vegetables from bac- terial action or other types of decay. Where sucha cellar is at hand it is, therefore, very well adapted to the preser- vation of fruits. Any other room, if its temperature could be controlled, would be just as good, and if it were light would be somewhat better than a cellar, which is usually dark. But rooms above ground are:generally lighted by windows, which make it difficult to control the tempera- ture. In the winter such rooms are pretty sure to have THE COOL CELLAR 155 a temperature below freezing in the cold climates, and this is sufficient to ruin fruits, most of which are spoiled by freezing. Since the value of the cellar in preserving fruits and vegetables is simply in its uniform and low temperature, the lower the temperature — provided it is above freez- ing —and the more even it is, the more satisfactory are the results. On the other hand, a warm cellar, so char- acteristic of most modern houses heated by furnaces, is of very little use in preserving foods, for decay occurs about as rapidly in such a cellar as it would elsewhere in the house, more rapidly, indeed, than in a cold pantry. Since one can purchase large quantities of many foods more reasonably in the fall by taking advantage of the low market rates, it is economy to have a compartment partitioned off from the heating apparatus in the cellar where fruits and vegetables can be stored. A cold closet is, indeed, almost necessary for the keeping of preserves. In the use of a cold cellar to preserve vegetables it is well to bear in mind that many of them — parsnips, car- rots, beets, turnips——are better preserved if buried in sand, and that fruits keep better in sawdust, oat chaff, or some other material which absorbs moisture. Other Devices. Any device for cooling will of course be useful in preserving foods. Cold running water, spring houses, submerging in ced water, are all used for the pur- pose. Suspension in deep wells is one of the most com- mon methods of obtaining a low temperature for milk, butter, etc., and is widely adopted in houses where ice is not at hand. Even the scheme of packing material in damp leaves may be of some value, since the evaporation 156 BACTERIA, YEASTS, AND MOLDS of the water from the leaves lowers the temperature. In warm climates this principle is made use of to cool drinks by keeping them in earthenware receptacles the surfaces , of which are constantly moistened. The evaporation of the water on the outside cools. the inclosed liquids. Cooling may be used for any kind of food. Three general rules should always be followed where food is put aside for preservation at a low temperature. 1. Cool the food as quickly as possible. This should be done before covering and setting aside for keeping. 2. Use every possible device for avoiding moisture. 3. Use food quickly after taking it from its place of storing, for such food when warmed decays rapidly. Tue Use or HEat The easy destruction of bacteria by heat suggests a means for increasing the keeping properties of many foods. Liquid foods may first be boiled and then cooled as quickly as possible, after which they may be put away in cold places for preservation. It is necessary that the material should actually be boiled, since a lower tempera- ture is not only useless but frequently detrimental. Ifa putrescible material is simply steeped in warm water and then put away, it will spoil rapidly; if it is boiled it may be preserved for some time. Boiling is useful for such materials as soups, stews, or any liquid not injured by boiling. It must be remembered, however, that boiling will not preserve the material indefinitely ; it simply delays the spoiling. CHAPTER XI THE USE OF PRESERVATIVES In early years the only means adopted for preserving food were drying and cooling, both of which have been known and used for many centuries. Within the last fifty years other methods have been used for the same purpose, and for some kinds of food they are far more satisfactory and valuable than those just mentioned. The first which we shall notice is the use of preservatives. The explanation of using preservatives is that it adds to the food something which will check the growth of microorganisms and thus prevent decay. Such preserv- atives must fulfill two conditions: (1) They must have some antiseptic power. (2) They must be comparatively harmless to man. Poisonous PRESERVATIVES Since we know that the spoiling of food is due to the growth of microdrganisms it is easy to find chemical sub- stances which will be perfect preservatives. If it were simply a matter of protecting food from decay, it would be the easiest thing in the world to bring about the result. But it chances that most of the materials fatal to the life and growth of microdrganisms are also poison- ous to man and therefore cannot be used in his foods. 157 158 BACTERIA, YEASTS, AND MOLDS This greatly restricts the number of materials that can be used for food preservation. Some it is quite impossiblé to use because of their violently poisonous nature. For example, carbolic acid and corrosive sublimate will preserve food perfectly, since they are fatal to bacterial growth; but they are also violent poisons to man and hence must not be put in his foods. There are other chemicals, how- ever, of a less poisonous nature which are frequently used for the preservation of foods. The milder drugs in use to-day for this purpose are chiefly borax, benzoic acid, salicylic acid, and formalin. Although these substances are poisonous and injurious to man when used in considerable quantity, they may be swallowed in small quantities without any appreciable effect upon the individual. But even in small quantities they have the power of checking the growth of bacteria, and they are frequently used for protecting various kinds of food from the spoiling that would otherwise occur. These materials, put up into proper form for use, can be found in our markets under a variety of commercial names. They usually go under special trade names, — pre- servaline, fruit preservaline, antifermentine, freezine, etc. These various commercial products differ in their chem- ical analyses, but are all made up of mildly poisonous materials. No two of these preservatives are exactly alike, but most of them are made up, wholly or in part, of the chemical substances above mentioned. The preserva- line products, for example, are largely borax, while the basis of freezine is formalin. They are undoubtedly effi- cient in protecting food from putrefaction and decay, for they all check bacteria growth. If used in sufficient COMMERCIAL PRESERVATIVES 159 quantity they will wholly prevent putrefaction, and even in small quantities they may so check the growth as to pre- serve the food much longer than usual. For this reason they are extremely convenient and have been widely used by people who do not understand what they are. Some have found them so convenient that they have given up the use of the refrigerator or other devices for producing cool temperatures, feeling that it is much cheaper, as well as more convenient and more satisfactory, to keep their food by adding a small quantity of preservaline or similar substance, than to use ice. The various forms of pre- servatives may be used for almost any kind of food, — for canning fruits or vegetables, for preserving milk, meat, etc., and, so far as concerns the actual protection of food from decay, they certainly accomplish their purpose. But the important question arises whether it is health- ful to use such materials in our food. Every one of them is of a morc or less injurious nature, and if taken into the body in any considerable amount will produce poisonous effects. This has led to much experimenting and discus- sion. In past years a considerable portion of the food products on the market has been treated with some of these food preservatives, — borax being widely used for this pur- pose. In the markets of Europe some of these substances are used to preserve a large part of the meats, butter, milk, etc. England obtains great quantities of her provisions from America and even Australia, and it seems difficult, or impossible, to deliver them at such long distances with- out treating them with preservatives. At all events, the foods coming from Australia to the markets of England are usually so treated. The use of preservatives in our 160 BACTERIA, YEASTS, AND MOLDS own country is less common, because our markets are nearer the sources of supply. The national Pure Food Law, making these preservatives illegal, has greatly reduced their use, and to-day the food on our markets is mostly free from them. It has been an open question for some years whether borax used in small quantities under such conditions is injurious to the consumer. Nor is the question yet posi- tively settled. It has become in a measure an interna- tional question, involving the importation of American beef and other products into foreign markets, and a great deal of contradictory evidence has been advanced. The fact that people have for years been unconsciously using food preserved by means of such substances, without any apparent injuri- ous effects, seems prima facie evidence that no harm results ; but it is possible, of course, to say that the harmful effects are not at first discernible, and that many of the digestive and other troubles of man are due to this unconscious con- sumption of such drugs. No positive answer can be given to the question. Although it is certain that many people in large cities have occasionally, or even constantly, consumed them without any apparent injury, the general belief is that they are injurious. Moreover, when such materials are used for preserving food, it frequently happens that a considerable quantity is unconsciously used. Our foods usually pass through the hands of several people before they are consumed. The original producer may put in a little preservative, the middleman adds more in order that the material may not spoil on his hands, and the householder, in ignorance of these additions, may put in a little more. By the time it PRESERVATIVES IN FOOD 161 reaches the table it may be so filled with some of these poisonous articles as to be decidedly unwholesome. In- stances are known where violent sickness, and even death, especially among children, has been traced to the use of such preservatives, which had been added by one person and another until the food contained them in large quan- tity. This is particularly true of milk, because it spoils so easily and quickly. For these various reasons the use of such preservatives is to-day forbidden by law in any food materials offered for sale, and they must also be condemned in the house, since even in small quantities it is possible that their daily use may cause trouble. It is also quite certain that if a preservative -is used at all, the food will occasionally contain so much of it as to be decidedly unwholesome, disastrous, or perhaps even fatal. No housewife should therefore depend upon any of these forms of preservation for her food. They are un- wholesome and even dangerous, and their use is liable to be followed by ill health and possibly by fatal sickness. Particularly should it be understood that it is dangerous to add preservatives to food that has previously passed through the hands of others who may have already used preservatives, —a condition of things especially likely to occur with milk. Nothing but universal condemnation for the use of the commercial materials can be given the householder. If any preservative is to be used, it is far cheaper and better to buy pure borax from the druggist. For milk or cream this may be used in the proportion of one quarter to one half ounce to six quarts of milk or 1 By a recent ruling a small amount of benzoic acid is allowed in certain foods. 162 BACTERIA, YEASTS, AND MOLDS cream; for preventing hams or bacon from molding or becoming slimy, the borax may be dusted on the surface, not more than one quarter of an ounce being used for each pound of meat. But any one of these materials, if used in considerable quantity, is certainly injurious, and this fact makes it quite out of the question to recommend them for home use. It is quite impossible for the physician, much less the housewife, to know how much may be used without danger. NoNpPOISONOUS PRESERVATIVES In protecting food by preservatives we are not confined to poisons, since there are a few materials capable of pre- serving food that are not poisonous but are, on the con- trary, beneficial to us. The use of such preservatives is of course perfectly proper. Some of them have been in use for many years and at the present time are more used than ever. The chief ones are mentioned below. Sugar. As already indicated, bacteria do not grow readily in pure sugar solutions, and if the solutions are very strong they do not grow at all. The other forms of microérganisms also, molds and even yeasts, fail to grow readily in solutions containing a considerable quantity of sugar. It is therefore quite feasible to preserve many of our foods from putrefaction by simply mixing them with a considerable quantity of sugar. Since sugar is an excellent food for man it does not injure the material but increases the food value of the product. As a preserva- tive sugar has more value against bacteria and molds than against yeast. It is the material which readily supports SUGAR AS A PRESERVATIVE 163 yeast life, and it occasionally happens that materials pre- served by it will ferment. But this does not commonly occur if the percentage of sugar is high, i.e. 40% to 50%. The use of sugar as a preservative is adopted in a number of well-known products. Fresh fish is occasion- ally preserved by rubbing with sugar. Condensed milk is preserved by the addition of 30% to 40% of it. It changes the nature of the milk, rendering it somewhat less digest- ible, but does not materially injure it as a food product. Jellies are also preserved from bacterial action, though not wholly from fermentation, by the large amount of sugar which they contain; for decay would take place quickly if it were not present. It has been used for a long time to protect fruits, in making what are known as preserves. Almost any kind of fruit may be preserved by stewing it with a large amount of sugar, equal parts by weight of fruit and sugar being commonly used. Ata moderate heat the fruit is so thoroughly impregnated with the preservative that no putrefactive organisms are subsequently able to grow in it, and it may then be preserved almost indefinitely. Marmatades are also preserved by the same preservative. This is also, in a measure, as we have seen, the reason for the preservation of raisins, figs, plums, etc., which are pre- served partly by drying and partly by the presence of sugar. In these cases the fresh fruit contains so much of it that none is artificially added. But most fruits contain too little to be preserved without the special treatment above described. There are of course decided limitations to the use of sugar for this purpose, for the flavors of most of our fruits are changed when mixed with a great deal of it. They cease to have fruit flavors and become a sort of 164 BACTERIA, YEASTS, AND MOLDS candied material which can be used only as a sweetmeat or a sauce. This method of preservation is used to-day much less than in earlier years before the wide extension of the process of canning. Salt. A more common, harmless preservative is salt. Materials thoroughly salted are completely protected from bacterial growth. Since salt is harmless and, indeed, a necessary ingredient in our food, such a method of pre- serving is quite legitimate. Salt is used as a preservative for a variety of food products. Fat pork is very easily pre- served by keeping it immersed in a strong salt solution called drine, producing what is known as salt pork. Corned beef and corned bacon are also preserved in the same way. Cheeses are sometimes preserved in brine, and the same is true of eggs. In other cases the salt is mixed with the food. ffams and some other meats are preserved partly by salt- ing, and in most forms of dried beef salt is added to assist in the preserving. It is used for the preservation of great quantities of jisk, particularly marine fish, which may in this way be preserved indefinitely from bacterial action. Fresh-water fish could be preserved equally well, but since they are not generally caught in large numbers they are rarely salted. The salting of du¢¢er is a procedure adopted partly for the purpose of giving a salty flavor and partly for the purpose of its preservation. In the preparation of cheeses salt is almost always used, for after their manufac- ture they are usually kept for weeks or months before they are ready for market, and salt is rubbed into their surfaces to prevent the growth of undesirable microérganisms. It must be remembered that, while salting preserves the material from decay, it does not preserve its fresh form. SALT AS A PRESERVATIVE 165 The flavor is much changed, and too large a quantity of salt meat is not wholesome. Moreover, salt somewhat changes the physical nature of food, so that it is not quite so easily digested. Salt foods, therefore, cannot wholly take the place of fresh foods. Experience has shown that when used in large quantities and unaccom- panied by plenty of fresh food they give rise to a kind of digestive derangement known as scurvy, a trouble fre- quently met with among sailors who have subsisted too largely upon salty foods. Nevertheless such foods are very useful, and if a quantity of fresh food is used with them they may be used very advantageously as part of our diet. In preparing such foods for the table they should be soaked in water to remove as much of the salt as possible. Vinegar. Acetic acid is another material used legiti- mately for the preservation of certain kinds of food prod- ucts. In its best known form, vinegar, it is the basis of the preservation of all kinds of pickles. The acetic acid in these cases serves two purposes: (1) It gives a new flavor to the material, rendering it very sour. (2) It pro- tects the product almost totally from the action of bacteria. The pickling of cucumbers has become a great industry, green cucumbers being more extensively used for the pur- pose than any other material. The vinegar is frequently mixed with spices, both for the purpose of added flavor and to aid in the preservation. Although pickled vegetables keep well, they do not keep indefinitely. Pickle brine sometimes becomes covered with a scum composed of bac- teria, and the pickles themselves may grow soft from decay. If the pickles are taken out and boiled for a few minutes, 166 BACTERIA, YEASTS, AND MOLDS the microdrganisms will be destroyed, the trouble may be checked and the pickles preserved. It is practically important to know that pickles should not be kept in glazed ware, since the acetic acid may unite with the glazing and make unwholesome products. Glassware receptacles are best for the holding of pickles. In a somewhat modified way acetic acid or lactic acid is the basis of certain other preserved foods. Sawer- kraut, for example, is cabbage protected from putre- factive fermentation by allowing it to sour and develop acids. Among these, acetic acid is somewhat prominent, but lactic acid is also found. The acid in this case is formed in the cabbage by the growth of acid-producing bacteria, and after it is formed it prevents the growth of other putrefactive bacteria, thus making it possible to preserve for a long time the vegetable material which would otherwise undergo putrefaction. Here we actually have an instance of one kind of harmless microérgan- ism protecting food from the action of other species. A similar food product is sometimes made from deans which are allowed to sour and are thus preserved from further decay. Any substance can be preserved from bacterial action if it can be soaked in vinegar or other acid, and it is therefore possible in the household to convert into either sour or sweet pickles a considerable variety of vegetables. The use of vinegar for this purpose is very limited, mostly confined to green fruits and vegetables, although fish or flesh is occasionally treated in the same way. The product obtained is used as a flavor to our diet rather than as a food. SPICES AS PRESERVATIVES 167 Spices. Many of the spices common in the household are more or less efficient as antiseptics, and when added to food material will preserve it from putrefaction. Their use is quite general in certain household products. For example, mince-meat is a watery mixture which under ordinary circumstances would readily putrefy. Both the meat and the apple in it would by themselves undergo putrefaction and decay; but when they are made into mince-meat, and spices, boiled cider, and some other mate- rials added, the entire mixture forms a mass which, though not absolutely protected from the growth of microérgan- isms, is ordinarily incapable of supporting the growth of the putrefactive and decaying bacteria which would natu- rally appear in the ingredients. The antiseptic effect is produced chiefly by the spices, and if the housewife should leave these out she would have a putrefying mass in a short time. Such material is not, however, completely protected from mold growth. It will keep longer if the apple is left to be added at the time of using, and, of course, it will keep best in a cool temperature. In a warm temperature the effect of the spices is not sufficient to prevent a more or less troublesome fermentation and decay, and particularly molding. In ordinary sausages and salads the same principle is concerned. Sausage meat is made of material which is subject to rapid putrefaction, but in cool weather it may be preserved for a long time. Here we have again an example of a readily putrescible material prevented from decay by the presence of the slightly antiseptic spices, like salt, sage, etc. The spices in the sausages have really a twofold purpose. Not only do they protect the 168 BACTERIA, YEASTS, AND MOLDS materials for a time from putrefaction, but they give to them the peculiar flavor which is desired. In the case of sausages, as in mince-meat, the spices are not sufficient to prevent putrefaction absolutely, and consequently in the warm summer weather it is not very easy to preserve them. Sausages, like mince-meat, are generally made in cold weather, for under such circumstances they may be preserved without trouble for a considerable length of time. : In a somewhat similar way, as we have already noticed, hops are used for aiding in the preservation of a yeast brew. They are also frequently used in making beer, to which they not only impart a desired flavor but also aid in preventing the decay of materials present which would readily support the growth of bacteria. Fruit cake of certain grades is preserved from spoiling chiefly by the spices it contains. Nearly all strong spices have an anti- septic power when mixed with foods, and protect them to a greater or less extent from bacterial action. This fact is made use of quite extensively by different nations; for most countries have special spiced foods preserved in this way, many of which are not known to people outside of the localities where they are made. Spices are thus of much value both as a means of imparting flavor and as a preservative, but they never preserve the original taste of the foods. Many spiced foods are used simply as condiments rather than as nourishment. CHAPTER XII PRESERVATION BY CANNING The addition of mild preservatives like sugar, salt, spices, vinegar, etc., while it makes possible the preser- vation of many kinds of food, very decidedly changes their nature. The flavor is totally changed, and in some cases the food is rendered less digestible; hence its food value is lowered. These methods of preserving food are very useful for some purposes, but they cannot be used for all kinds of food. In many cases the change of flavor would be so decided and the change in the nature of the food so great as largely to destroy the material for subse- quent purposes. None of the methods preserve the food in anything like its natural condition. Wuart 1s CANNING? A method of preservation based upon the simple plan of keeping bacteria away from food products has been devised in the last century. This has come more and more into common use, until to-day it is employed to an almost incredible extent. The method is spoken of as canning. The food is not treated by any antiseptic for the pre- vention of bacterial growth, but reliance is placed simply upon devices for keeping all bacteria from it. If this can be done, the food will not be subject to their action, and will never spoil. 169 170 BACTERIA, YEASTS, AND MOLDS We have already noticed that bacteria are almost uni- versally distributed in earth, air, and water. This fact makes it extremely difficult to protect food from their action, and, indeed, without special devices it is quite impossible to do so. All food material—meats, fruits, or vegetables —is sure to contain bacteria when it reaches the home or the canning factory. From some source, either air, water, or earth, every kind of food material is sure to become contaminated. Every one must recognize, then, that bacteria will be found with absolute certainty in every kind of fresh food. Hence the process of keeping food by protecting it from bacteria must consist of two steps: (1) Some means must be devised for removing the bacteria already present in the food. (2) The access of all other bacteria must be absolutely prevented. If these two objects can be accom- plished, the food will be protected from bacterial action and, thus protected, may be preserved zudefinitely. Food thus guarded may be kept for any number of months. No limit has ever been found, and we have no reason for ques- tioning that it might be preserved for centuries without any subsequent change, provided it could be kept abso- lutely free from the attack of microérganisms. This method, therefore, offers almost unlimited possibilities in the way. of preserving food for future use. It demands care in its application, but the results, when properly obtained, are permanent. 1. Destroying the Bacteria Present. The removal from any food material of bacteria already present is generally brought about by the action of high heat. We have already noticed that a sufficiently high heat is fatal to all STERILIZATION FOR CANNING 171 forms of life, and hence the simple heating of food will destroy all bacteria. The material to be canned must be cut up into pieces of convenient size, which will depend somewhat upon the kind of material. In general, the larger the pieces, the more attractive the appearance of the product when finished but the greater the difficulty of canning. Cherries, plums, and berries can be left whole. Pears are cut into halves or quarters, while apples are commonly cut into smaller pieces. These pieces are to be placed in water and the whole brought to a brisk boil, this temperature being chosen because it is easily obtained and because it is sufficient in most cases to destroy the bacterial life. The process of canning is, therefore, applicable only to materials that are not greatly injured by immersion in water and subsequent boiling. Hence it is useful for foods which cannot be well preserved by drying. In the application of heat several points must be borne in mind. 1. It must be remembered that the destruc- tion of the bacteria must be absolute. If a single indi- vidual bacterium is left alive in the food after the boiling, the whole process is useless, and the canning will be a total failure. One live bacterium will be capable of grow- ing and multiplying, producing a subsequent putrefaction and destruction of food with just as great certainty, though not so quickly, as if a million of them were left alive. The preliminary heating must therefore be a complete sterili- zation, that is, a heating so thorough that every individual bacterium is destroyed. No half-way processes are of any use whatsoever; it must be total and absolute. This is by no means easy, and most failures in canning are due to the inability to bring about this complete destruction. 172 BACTERIA, YEASTS, AND MOLDS If a housewife finds that a portion of her canned preserves is spoiled, she may be sure that the original heating was insufficient. 2. It must be remembered that the amount of heat required to destroy different species of bacteria is not always the same. While most actively growing bacteria are destroyed by a moderate heat, and quickly killed by boiling, certain bacteria spores, as already noticed, are capable of standing much greater heat. Some kinds of bacteria produce spores that may be boiled for a few moments, or, indeed, for an hour, without being wholly destroyed. From this it follows that a short boiling is not always sufficient to destroy bacterial life. If the food material chances to contain some of these resisting spores, the brief boiling commonly adopted in the pro- cess of canning will not kill them, and it will inevitably happen that the food, if canned, will undergo putrefac- tion because of the growth of the spores that were left uninjured. If on the other hand the food in question does not chance to contain such spores, a few moments’ boiling is quite sufficient to protect the material perfectly from later decay. It is a well-known fact that the process of canning is not equally successful with all kinds of foods. Some sub- stances (rhubarb) contain a material that acts as a par- tial antiseptic and can be preserved very easily. Others, like most fruzts, require a little more care, but are easily preserved ; while others, in spite of the ordinary precau- tions, will frequently show subsequent signs of decay. The canning of tomatoes has always given trouble to the housewife. In former years it was thought to be an DIFFICULTIES OF CANNING 173 impossibility to can gree corn, and the preservation of peas and Jeans has proved to be even more difficult. While all of these products are successfully preserved by canning to-day, it is chiefly done in factories; for they are far more difficult to preserve in this way than a large number of other foods which are more commonly preserved in the home. The problem of canning any product, whether it be fruit, tomatoes, corn, or peas, is simply that of totally destroying the bacteria that may be present. Ifthe material chances to = Zz contain only the bacteria that are Af > G, ; ef 6 0 unable to produce spores, as with a3, most fruits, it is quite easy to oO ® destroy them by simple boiling. Giihe Sai8 Green corn, however, has been a found by microscopic study to con- Fic. 63. Spore-producing tain a considerable number of acer- _ bacteria found in canned tain kind of bacteria which develop one spores capable of resisting very high heat (Fig. 63). These bacteria have been found on the corn husks while grow- ing in the field, on the corn cobs, and also in the green corn. They are difficult to destroy by heat, and hence the successful canning of corn has been regarded in past years as an impossibility. The presence of two or three or even one of these highly resisting spores may be quite sufficient to make the ordinary method of can- ning quite ineffectual. Although little microscopic study has been directed to other similar problems, like the can- ning of tomatoes and peas, there is no doubt that the trouble is due to the presence of spore-bearing bacteria which resist the temperature of ordinary boiling. 174 BACTERIA, YEASTS, AND MOLDS The remedy in all such cases is greater heat, since no satisfactory means of destroying bacteria is known except the application of heat. Even spores may be perfectly destroyed if the proper method is adopted. Higher Heat. Common liquids, when boiled in open vessels, cannot be heated above 212°, no matter how brisk the boiling ; but if boiled in closed vessels under pressure the temperature may be raised much higher. A tempera- ture of 212° does not destroy spores, but a few degrees higher will doso. If the material is boiled under pressure of a few pounds only, such a temperature is easily obtained, and if it is maintained for a short time the spores will be destroyed. In the household it is rarely possible to use apparatus for this purpose; but in canning factories there is no difficulty in constructing and using devices for heat- ing under pressure. This method of heating is commonly adopted for the sterilization of food products which are difficult to can because of the presence of spores. Longer Heating. Higher temperatures are not easily obtained in the household, but the spores may be killed by simply prolonging the boiling. If spore-bearing mate- rial is boiled for a sufficient time, the spores are eventually totally destroyed. The length of time necessary for the purpose cannot be stated exactly, for it will depend very largely upon the vigor of the boiling and the nature of the _ food. For the thorough sterilization of peas an hour, or even two hours, may be needed, and an equal time is required for corn or beans. Tomatoes do not require quite so much time, Any material will be more surely sterilized if placed at first in cold water and then brought to a boil, than if placed immediately in boiling water. HERMETICAL SEALING 175 Nearly all failures in canning are due to an insufficient amount of heating at the outset. In the canning of fruits, which is the kind of preserving most commonly performed at home, there is seldom any special difficulty, since fruits do not as a rule contain resisting spores. In the majority of cases, therefore, a vigorous boiling of fruits for a few moments is sufficient to destroy bacterial life, after which the materials can be canned with perfect success. It must be remembered, however, that absolute certainty cannot be reached by simple boiling, and that the employing of this method will result in occasional failures. Once in a while a can will become decayed, though the rest of the same lot will be preserved in the proper fashion. The difference in these cases is doubt- less due to the accidental presence of some spore-producing bacterium which happened to get into one of the cans and not into the others. 2. Preservation. After the food has once been de- prived of bacteria (stert/ized), it must be protected from the subsequent access of all kinds of microérganisms. Since bacteria are always present in the air, any of these sterilized products will surely be reinoculated if exposed, and the new bacteria would soon spoil the food. The practical method of keeping bacteria out is, there- fore, that of sealing the contents hermetically. In the laboratory it is possible to preserve foods without sealing by simply filtering all the air that reaches them through something fine enough to exclude bacteria. Bacteriolo- gists have found that the air which passes through cotton is deprived of all bacteria. If, therefore, any sterilized material is placed in bottles, tubes, or vials which are 176 BACTERIA, YEASTS, AND MOLDS tightly plugged with cotton, as shown in Fig. 64, it will be perfectly protected from the invasion of bacteria. A Fic. 64. Pre- served cher- ries, showing that the ex- clusion of air is not neces- sary for pres- ervation. knowledge of this fact may be of some practi- cal importance, even in the household, in case it is desired to preserve something for a short time only and one does not want to goto the trouble of hermetical sealing. But such a method is quite impracticable for the ordi- nary canning of food. At best it is of only temporary utility, for, though cotton keeps all bacteria away from the sterilized material, it will not wholly exclude molds, and there- fore cannot preserve indefinitely. flermetical sealing, which will prevent all subsequent access of air, is extremely easy to accomplish and is thoroughly effective. The material must be sealed in some proper re- ceptacle whzle still hot from the boiling, for it is at this time sterile, and if sealed at once has no opportunity of becoming inoculated with more bacteria. The devices for hermetical sealing are numerous. In earlier days the housewife employed ordinary bottles, which were filled with the material, then plugged tightly with corks, and sealed with rosin or something of the sort to exclude all air. The invention of the modern fruz¢t jar with its rubber ring and convenient top has done away with all such crude devices. The fruit jar with its variously devised top is a perfectly effectual means for excluding air and hence THE FRUIT JAR 177 for keeping out all microdrganisms (Fig. 65). The sig- nificant feature of these fruit jars is the rubber ring a, which is clamped tightly upon a flat ledge on the jar c, by means of the cover 4, so made that heavy pressure can be exerted upon the rubber. This pressure upon the rub- ber effectually excludes all air and all bacteria. Fresh rubber rings should be used each time the jar is filled, since the efficiency of the sealing depends upon the soft- ness and elasticity, of the rubber; if this , gets hard, as it will in a few months, the sealing will not be effectual. Of course the whole jar must -be sterilized before Fic. 65. The top of a common fruit jar. being filled. To do At ais the rubber ring upon which the suc- cess of the sealing is dependent. this it is best to place it in cold water, bringing the water to a vigorous boil, and then fill the jar while it is still hot. The glass fruit jar is almost universally used in the “home, is very convenient, and can be used again and again, But in canning factories the use of tin cans is largely adopted, since they are less expensive and are to be used but once. The principle of their use, how- ever, is exactly the same as that of the glass jar, although the details are different. The material to be canned, with or without previous boiling, is put in the tin can, upon which a cover is placed and sealed firmly by sol- dering, the whole now being closed to the air except for a small opening in the cover. Then the can, with 178 BACTERIA, YEASTS, AND MOLDS its contents, is placed in a convenient heating appa- ratus for thorough sterilization, the opening in the top being sufficient for the exit of steam and for preventing internal pressure, which might give rise to an explosion. In some factories it is sometimes customary to heat the product in a bath of CaCl, which makes it possible to obtain a temperature of 260° — quite sufficient to sterilize the contents of the can, even though it contain resisting spores,.as will be the case with peas or corn. While the material is still hot a drop of solder is placed upon the opening in the top of the can. This thoroughly seals it and the work is done. It is customary to keep the cans in the factory for a while in order to test the efficacy of the work. Any cans which later are found to be swollen, indicating the accumulation of gas on the inside, are discarded as ruined. In the ordinary process it fre- quently happens that an occasional can cither fails of ster- ilization or of complete sealing; the result of which is a subsequent ruin of the product. Canning factories some- times suffer great loss from the spoiling of their products. In all these cases the cause is probably the presence of resisting spores, and the remedy is the application of greater heat. A knowledge of this fact has enabled can- ning establishments in recent years to avoid in great measure their previous losses. In certain kinds of canned food it has been customary to add some mild antiseptic to aid in the subsequent preserva- tion. The material most commonly used for this purpose is borax, which is frequently found in cans of meat. Its purpose is to check the development of any bacteria that may be left in the meat after the process of canning. PRESERVATIVES USED IN CANNING 179 From the facts already given it will be seen that the presence of borax in canned foods is totally unnecessary, provided sufficient care is taken in the canning. Its use was a means of covering up a lack of thoroughness in canning, and it has been found in the cheaper products. If the-material had not been heated enough to produce complete sterilization, it might still be preserved in cans if sufficient borax were added. In large packing factories where a great amount of food, particularly meat, is to be canned at once, it had become quite common to use a certain amount of such a preservative to cover up this lack of complete sterilization and prevent subsequent loss. The method is of course more economical, because it does not require so much heat and because there- is a very much smaller per cent of loss. Whether the material thus preserved is unwholesome is a question that has not yet been positively settled, but the sale of it is to-day forbidden by the national Pure Food Law. In fruit canning in the household it may be given as a universal rule that no dis- infectants of any sort should be used. If the housewife cannot satisfactorily preserve her fruits without them, she would do very much better to depend upon the commercial products which she can buy at the store. At all events, no one should under any circumstances resort to the use of borax, preservaline, antifermentine, or any of the other materials put upon the market for preventing fermentation. They are dangerous to use, they are at least partly poisonous, and their use in any form should be absolutely avoided in domestic work. Practically any type of food can be preserved by can- ning. Some materials, however, are very much more 180 BACTERIA, YEASTS, AND MOLDS easily preserved than others. Meats are preserved with great ease, but it is rarely worth while in the household to can meat, since fresh meat can be bought in civilized countries at all seasons of the year. When one wants canned meats it is better to depend upon the product bought in the market than to go to the trouble of canning. The same may be said of tomatoes, corn, peas, or beans. All of these materials may be canned successfully in an ordi- nary household, but it requires long heating and special care, and at best there will be many failures. Consequently such materials, when canned in the home, may be very expensive because of the considerable amount that must be thrown away. In the canning factory, however, because of greater experience and better facilities, these foods can be preserved much more successfully and cheaply. Moreover the commercial products in these cases are of a very satisfactory quality and very cheap. If for any reason a housewife has on hand a large quantity of tomatoes which must be canned or thrown away, it may be econom- ical to can them at home, always remembering that they require more heat and more care than most other fruits. But except under such conditions it is better and cheaper to depend upon the market for canned tomatoes, peas, and corn. The market products are more reliable, consider- ably cheaper, and usually nearly or quite as good as those obtained by home canning. Concerning other materials, however, it is economical and frequently advantageous to adopt the process of can- ning in the household. Most forms of fruit —afples, pears, cherries, peaches, grapes, berries, etc. —are canned without much difficulty, requiring only a moderate boiling VALUE OF CANNED GOODS 181 and a careful sealing in fruit jars. The material thus prepared is usually of a better flavor, because more care- fully prepared, and more satisfactory than much that can be bought in the markets, in the preparation of which wholesale methods have been necessary. For the house- hold, therefore, canning is chiefly applicable to fruits, and it furnishes a means of keeping for winter use many delightful delicacies. The process of canning has wrought a wonderful change in civilization. It has made possible the use of great quantities of material which previously were sure to decay before they could be used. It is possible to take any crop which is produced in abundance during a short season and preserve it indefinitely for future use. It has brought about a great expansion of the food possibilities of the human race and a very great change in the habits of civilization. Canned food is, however, always changed in character by cooking, although materials which are ordinarily cooked before they are eaten may, of course, be canned without further change. The most noticeable effect of the process is the total disappearance of the original flavors. Canned fruit has a flavor of its own and oftentimes a very pleas- ant one, but the flavor of the fresh fruit is usually more agreeable. Experience has shown that a diet of canned foods alone is not wholly satisfactory, although arctic explorers have learned that they can live upon them much more healthfully than they can upon salt foods, which were the staple diet on shipboard before the extended adoption of canning. Canned foods are valuable, but they should not be used exclusively. CHAPTER XIII MILK; EGGS; PTOMAINE POISONING BAcTERIA IN MILK It is more difficult to preserve a supply of good milk than of almost any other food product. This is due to three reasons : (1) The number of bacteria, under ordinary circumstances, is greater than in any other food product. (2) Milk furnishes an exceptionally favorable food for bacteria. (3) The changes which these bacteria produce in milk are very decided and take place with great rapidity. These three factors together make it difficult to preserve milk in the household without exceptional precautions. The bacteria present in milk are not only numerous, but they comprise many kinds (Fig. 66), Milk as it is secreted by the healthy cow does not contain bacteria, but it has a chance of contamination with microérganisms from a variety of sources, and even a few moments after the milk has been drawn it contains organisms in large numbers. The chief sources of these organisms are: (1) the bacteria in the milk ducts which are washed into the milk can during the milking ; (2) the dust that is likely to be floating in the air of the barn or milking stall where the milk is drawn; (3) the milk vessels, which are rarely washed perfectly clean; (4) the dirt and filth that are always clinging to the hairs of the cow and which fall into 182 PTOMAINE POISONING 183 the milk pail during the milking ; (5) bacteria from the hands and clothing of the milker. The number of bacteria found even in fresh milk is extremely great, particularly if the milk be drawn without special precautions for cleanliness. Thousands and even hundreds of thousands are sometimes found in each cubic inch. These bacteria grow rapidly, inasmuch as milk is warm when drawn from the cow, and by the time it reaches the con- sumer in the city the milk is likely to contain these microérganisms in incredible numbers. The exact numbers, Fy. 66. Milk as shown under the microscope, show- however, are mat- ing numerous bacteria. 2, common lactic bacteria ; ters of no special 4, common cocci; ¢, fat globules; d, cells. importance to us, for fortunately most of the bacteria in milk are harmless. Some of them, indeed, are useful, and, while occasionally troublesome bacteria get into milk, as a rule we may look upon the milk bacteria as doing no injury to the health of the person drinking it (Fig. 67). Effect of Bacteria upon the Milk. But the housewife is interested in the effect of the growth of bacteria upon the milk itself. The bacteria which grow most rapidly in 184 BACTERIA, YEASTS, AND MOLDS milk belong to a type known as lactic bacteria (Fig. 67). These produce a change in the milk sugar, converting it into lactic acid, which causes the milk to taste sour and curdle. Curdling and souring will never occur if bacteria can be kept out of the milk. Oo Soe £330 0 OR eoco °8 SP 0885 55°0 3.0 Res re) Z foe) oO 2 3 “tlt XR > IX = ; cod st? avg ol ©" x? @ aes ai b eS a Lig So, 7 ALIS 0° & COD SO oom Ye \ ° SP 9 = Zo Fic. 67. Group of milk bacteria. x, the most common lactic bacterium, B. dactds actdi; 2, a less common lactic bacterium, B. lactis aerogenes ; 3, common cocci found in milk; 4, a bacillus producing cheese flavors; 5, a common bacillus with no action on milk, B, subtilis; 6, a bacillus causing slimy milk, B. lactis viscosus ; 7 and 8, com- mon organisms with no action on milk; 9, bacillus causing swelling of cheese; 10, a bacillus causing milk to become putrid. Although the souring is a nuisance, it does not injure the wholesomeness of the milk, and sour milk could be used freely were it not for its unpleasant taste. Indeed, souring is, under some circumstances, desir- able, since milk properly soured is protected from a variety of other changes far less agreeable. If the lactic bacteria do not cause the milk to sour, it'is almost sure to putrefy, and putrefaction is far more unpleasant and unwhole- some than ordinary sour- ing. The souring of milk, therefore, is a natural phe- nomenon, and one that should be expected and desired in milk after it has become a day or two old. Milk which will not sour is suspzczous, unless it has been kept at a very low temperature for preservation. Sometimes milk a day or two old becomes slimy or slippery to the touch, rather sweetish to the taste, and is PRESERVATION OF MILK 185 ruined for all practical purposes. There is no special rea- son for believing that such milk is unwholesome; but people will not drink it since it is not normal milk. Milk occasionally undergoes a sort of putrefaction, becoming tainted in smell and taste. Sometimes it becomes d/ue or ved, and occasionally other changes take place in it. Practically all of these phenomena are due to different species of bacteria, and they may all be prevented if the growth of the microérganisms can be held in check. None of them, however, produce so much trouble in the household as souring, and although, from the standpoint of health, some of these other types of bacterial action are more serious than the souring, the latter is the phe- nomenon which produces the greatest inconvenience. PRESERVATION OF MILK The preservation of milk, which commonly means pre- venting the milk from souring within too short a time, is, accomplished only by checking the growth of bacteria. In considering the question of furnishing the household with good, sweet, wholesome milk, several factors are involved which must be considered separately. 1. Source. Every housewife should be very particular about the source from which she obtains her milk. This is a matter frequently overlooked, and milk is obtained without special consideration as to its source, upon the general assumption that all milk is alike and that it makes little difference from whence it comes. This is common in the families of the rich and the poor, because the former leave the purchase to servants, and the latter are 186 BACTERIA, YEASTS, AND MOLDS likely to buy the cheapest quality. No article of food should be so closely scrutinized, for, although the legal safeguards which the public milk inspection places around our milk supplies insure a tolerably good chemical quality, there is a great difference in the product from different sources. It is an absolute rule that cheap milk 7s always poor milk, and the cheaper the less its value. It is not economy to purchase poor milk, for, although there may be a saving in the original purchase, the amount of food bought is less and the danger attending its use is much greater. Recognizing, then, that its value is in propor- tion to its cost, we notice the kinds of milk that may be purchased in the modern city. Sanitary Dairies. Certified Milk. The most expensive milk comes from special dairies where great care is taken to keep everything in proper sanitary condition. The cows are kept in first-class health and are under the care of a veterinarian. Every precaution is taken to exclude . contagious diseases from contact with the dairy, and care is taken to keep everything clean and sanitary. For all this care the dairyman must of course be reimbursed by the consumer, and he is obliged to charge a higher price. In the vicinity of our larger cities many of these dairies have grown up in the last few years and are to-day furnish- ing an exceptionally high grade of sanitary milk, for which the charge is commonly from twelve to fifteen cents per quart. Such milk, though the most expensive, is undoubt- edly the best and is far safer than the ordinary milk. A modification of this method is the sale of what is called certified milk. This is milk that is sold with the cer- tificate of a special commission, commonly composed of TYPES OF CITY MILK 187 physicians. This commission, by means of chemical and bacteriological tests and sometimes by visits to the dairies, insures itself that certain dairies produce milk of good character and under unexceptionable conditions. Exam- inations and tests of the milk are made frequently, and if it comes up to the high standard which is set, the com- mission gives the dairy its certificate, which is then placed upon each bottle of milk sold. Such a certificate assures the customer that the milk is thoroughly reliable. Milk from the Ordinary Milkman. Milk from the com- mon milk supply is less reliable and costs correspondingly less. Sometimes this milk is of a good character, perhaps of as high a grade as that from the sanitary dairies. At other times, however, such milk is not satisfactory, because it is. produced under conditions of unimaginable filth. There is no way for the consumer in a large city to deter- mine whether the milk from the milkman is reliable; and if milk is to be purchased from an ordinary milk supply, one must be content with such legal regulations as the state can devise for protecting the quality of milk. If one lives in a small community where the milk is distributed by the producer himself, it is quite possible to know more about its quality; for a little care in selecting the most cleanly milkman will ordinarily result in obtaining milk that is thoroughly satisfactory. Grocery Milk. The poorest kind of milk that can be purchased is that upon which the poorer classes in cities largely depend. This is obtained from groceries, and is bought in small quantities. This method of purchasing is a necessity with the poorer classes who have no re- frigerators, for in warm weather it is quite impossible to 188 BACTERIA, YEASTS, AND MOLDS preserve milk in a tenement house without. the use of ice. The grocer keeps the milk on ice, and the customer buys it in small quantities to be consumed at once. This would be a proper arrangement if it were not for the fact that poorer kinds of milk find their way into these groceries, and are likely to be kept until old, so that as a rule the milk thus purchased is the poorest grade that reaches the market. It is usually sold at a small price, but is of such poor quality that the poorer classes themselves would be much wiser to purchase a better grade. By the removal of part of its water the keeping property of milk may be increased. Condensed milk is such a prod- uct, which, after condensation, is commonly preserved by the addition of about 40% sugar or by sterilizing. It is a useful product, but cannot exactly replace fresh milk. A type sometimes called concentrated milk has three quarters of its water removed by evaporation at 140°. This destroys disease germs and brings the milk into a condition in which it will keep for many days. When, subsequently, the water is restored, the material is indistinguishable from fresh milk and will be easily substituted for it. But our care should not cease with the scrutiny of its source. Even though originally of the highest character, milk will not keep in our homes unless properly treated. The keeping of milk depends upon temperature and cleanliness in the pantry. 2. Milk Vessels. Special care should be given to the vessels in which milk is received and kept. A large part of the trouble which the housewife experiences in keeping milk is due, not to the milkman, nor to the character of the milk which she purchases, but to the condition of the PRESERVATION OF MILK 189 vessel in which she places it. A milk pitcher used day after day becomes filled with lactic acid bacteria, and any fresh milk poured into such a receptacle will be sure to sour in a very short time. This fact a housewife fre- quently overlooks. Milk vessels should be cleaned with the greatest of care and should be thoroughly scrubbed with boiling water in which there is considerable soap. The soap “cuts” the grease and cleans the dirt from the milk vessels, and the boiling water kills part of the bac- teria ; so that through the agency of the soap and the boiling water the milk receptacles are pretty thoroughly cleaned. Glass vessels are more satisfactory than others, since it is much easier to tell whether they are clean. Glass, however, is easily broken in hot water, and care must be taken in the cleaning. 3. Temperature. The effect of temperature upon the keeping of milk is more striking than upon that of any other food product. Since milk may be frozen, it may be kept in that condition for weeks, months, or even years without change. It is rarely possible to preserve milk in this way, however, although freezing has recently been adopted in some communities as a means of furnishing fresh milk to the public. But other means of cooling are in constant use. Milk is frequently placed in a cellar, since the temperature is lower than in the rest of the house. Another widely adopted plan is to lower the milk into a well, where, since it is near the water, it is cooled. An even more practical and widely used device is the ice chest, in which low temperature can be easily maintained. The lower the temperature the better the results, and con- sequently the more ice used the better. The ice chest has 190 BACTERIA, YEASTS, AND MOLDS become a practical necessity for families who try to keep milk for even a few hours in hot weather. If not cooled, milk will sour very rapidly. Ina moderately warm room it will keep for a few hours only, and in summer it will some- times sour almost as soon as delivered to the customer. The housewife should, therefore, place the milk in as cold a place as she can find zmmedtately after receiving it from the milkman. One caution must be given in regard to milk preserved at low temperatures. If milk is put in an ice chest with a temperature in the vicinity of 40°, it may keep for many days or even weeks without souring. It is usually assumed that milk is perfectly good and whole- some so long as it is not sour. This is based upon the assumption that the only important change to be feared is souring ; so that if it is not sour it is almost universally regarded as wholesome. Nothing could be further from the truth, for, although the lactic bacteria do not grow at low temperatures, certain other species do grow readily enough. Milk kept in an ice chest for many days, even though perfectly sweet and showing no trace of souring or curdling, usually contains great numbers of bacteria. The bacteria that grow under these circumstances are likely to be more injurious to health than the lactic bac- teria. The latter are not injurious, although they render the milk unpleasant ; while the bacteria that grow at low temperatures are, some of them at all events, mischie- vous forms, and the milk may, therefore, be made very unwholesome by them. If any unusual smell or taste should appear in milk which has been kept for a day or two in an ice chest, it is not fit to drink, for this means STERILIZATION OF MILK IQ that unusual types of bacteria have developed to great extent and have probably made it unwholesome. 4. Use of Preservatives. The facts given elsewhere concerning the use of preservatives apply equally in the case of milk. The use of any preservative is always to be deprecated, and, so far as concerns the housewife, the rule should be that no preservatives should ever under any circumstances be used in milk. It should be borne in mind that none of these devices remove dangerous disease germs. They make it pos- sible to keep the milk longer, but do not make it more wholesome if it chances at the outset to contain any mischievous bacteria, 5. Sterilization. Sterilization of milk has become extremely common in the last fifteen years. It has been recommended widely by physicians, it has been introduced by milk-supply companies, and it has very frequently been adopted in private families. In our large cities, during hot weather, families unable to obtain ice protect their milk by heating it. The most common method is that of simple dozing, a boiling temperature being sufficient to kill most of the bacteria present. Not all of the bac- teria are killed by this method, and hence the milk is not strictly sterilized, for this term means the destruc- tion of all bacteria. But the boiling does destroy most of them, and since it is an extremely easy method to use, the boiling of milk is a very general practice. Absolute sterilization is possible by using a heat higher than that of boiling, but this cannot be done in the ordinary kitchen. In common use sterilizing simply means boiling, and we shall so use the word, although it is not strictly correct. 192 BACTERIA, YEASTS, AND MOLDS The purpose of steriization is twofold. (1) It delays the souring of the milk. Milk that has been boiled may keep from souring for several days, whereas without boil- ing it will keep only a few hours. With the poorer fami- lies in cities this is the chief purpose of boiling the milk, since it will not keep more than a few hours without ice, and they have no ice chests where it can be preserved from souring. (2) The destruction of disease germs. Milk is a common means by which certain contagious diseases are distributed through a community. The diseases in question are produced by bacteria in the milk, and boiling destroys them. This is the ground upon which physicians and health boards have in the past few years so widely advocated the boiling of milk that is to be used for drink- ing. Since boiling does destroy practically all the disease germs liable to be in milk, it makes it incapable of dis- tributing contagious diseases. There are certain disadvantages in boiling milk. The taste is wholly changed, for boiled milk is quite a different article from raw milk. Most people do not enjoy the taste of boiled milk, and the adoption of sterilizing or boiling will, therefore, greatly reduce the amount of milk used as a food. It might indeed be possible to learn to enjoy the taste of boiled milk. Children brought up on it like it, while they cannot endure the taste of raw milk. A more serious objection to sterilization is that the heating so changes the nature of the milk that it is less easily digested and assimilated. Boiled or sterilized milk can be digested and assimilated readily enough by persons with strong digestive powers, and many children are satis- factorily brought up on it; nevertheless it is somewhat PASTEURIZATION OF MILK 193 more difficult to digest and assimilate than raw milk, and frequently children with weak digestive powers do not flourish when fed upon such milk. This is a serious matter and has prevented the widely extended use of sterilized milk. Because of these objections the practice of sterilizing has not increased in the last few years as it was once believed it would. 6. Pasteurization. — The objections to boiling have led to the adoption of a different method of treating milk for the purpose of accomplishing the same results. Pasteur- izing is also dependent upon the use of heat, but a lower degree than that of boiling is used. The temperature adopted for this purpose is commonly between 145° and 170°, sometimes running slightly above or below these limits, and the milk should be kept at this temperature from ten minutes to half an hour. /¢ must then be cooled rapidly. It may seem strange that the use of a lower tempera- ture than boiling should be more satisfactory than boiling. The reasons, however, are simple enough. The bacteria which sour the milk do not produce spores and are, there- fore, nearly all killed at a temperature of 145° Consequently, pasteurized milk will keep much longer than unpasteurized milk. Furthermore, all disease germs that are most liable to be present are also destroyed by this low temperature. The diseases ordinarily distributed by milk are produced by bacteria that do not develop spores, and a temperature of 140° for half an hour is sufficient to destroy such bacteria. Moreover, the disagreeable changes produced by boiling do not appear at the pasteurizing temperatures. Pasteurized milk does not have the taste of boiled milk, 194 BACTERIA, YEASTS, AND MOLDS and is nearly as easily digested and assimilated as raw milk ; hence the objections raised against sterilization do not apply to pasteurization. On the other hand, there is one practical objection. In an ordinary household it is almost impossible to find one em- ployed in the kitchen who can satisfactorily use a thermometer, and it is out of the question to expect any ordinary servant to heat milk at a temperature of 140° for half an hour. Fic. 68. Apparatus for home pasteurization of milk. The figure on the right shows method of cooling the milk by running water. The only way it can be accomplished is by some device which will bring about the result in a simpler way. The most con- venient apparatus for this purpose is that shown in Fig. 68. This consists of a series of bottles which readily fit into cylinders placed in a larger vessel. This receptacle is filled with boiling water, and the bottles, filled with milk, are placed in the cylinders. The whole is set aside to cool. The milk is warmed by the hot water surrounding it, and the water is at the same time cooled by the milk. The size of the vessel is so proportioned to the bottles that, when properly used, the milk is heated to about the temperature desired PASTEURIZATION OF MILK 195 before it begins to cool. The method of using this pasteur- izing apparatus is extremely simple and can be followed satis- factorily in any kitchen. Where such an apparatus is not obtainable, the same object can be accomplished in a still simpler way. Place the milk in quart glass jars. Fill a pail with boiling water and place the jars of milk in it. The amount of water should be such as to come nearly up to the top of the jars. The pail should then be set aside to cool, and the milk should be occasionally stirred. The result is that the milk is warmed to about the temperature desired before it begins to cool. After the heat- ing, the milk should be cooled rapidly by running cold water into the pail, this step being as important as the heating. Pasteurization has been widely adopted in the last few years, and its use is increasing. Indeed, in some of our larger cities ordinances have been passed requiring the pasteurization of all milk except that from cows which have been tested by tuberculin. The reason for such ordinances and for the in- creasing of the use of pasteurization is the recognition of the fact that it is impossible, by any ordinary safeguards, to so protect the milk as to render it perfectly. safe. It is cer- tainly not safe at the present time to feed babies upon ordinary unpasteurized market milk. In most of the larger cities pas- teurized milk may now be purchased, though some dairy firms pretend to pasteurize their milk without doing so effectively. They heat it somewhat, but not high enough to destroy the disease germs. Such milk is sometimes called ‘‘ commer- cially pasteurized,” and it is frequently worse than the ordi- nary unpasteurized milk. For this reason there is a strong tendency now to insist that pasteurization should be done under official inspection, and when such inspection is given, the milk may be relied upon as safe. 196 BACTERIA, YEASTS, AND MOLDS One caution should be given regarding the use of pas- teurized milk: the milk must be used quickly after pas- teurizing. It is true that such milk may keep for two days without difficulty, but bacteria are growing in it all the while, and although the milk does not sour it soon becomes unfit todrink. Hence pasteurized milk must be used quickly, at least within twenty-four hours from the time when it was pastcurized, and meantime it should be kept cool just as if it had not been pasteurized. The most important rule in regard to the use of milk in the household is that it should be used fresh. No satis- factory method of keeping it can prevent all bacteria from growing, and although the usc of ice and of pasteurization or sterilization may keep it in a drinkable condition for a day, two days, or even longer, it is always suspicious after it has been kept for this length of time. Milk is plenty old enough by the time it reaches the house, and it should therefore always be used fresh. It is far better to obtain it frequently, in small quantities, using it up as soon as possible after it reaches the home. : Above all it- should be emphasized that clean milk ts better than pasteurized milk. The proper procedure is to obtain milk in good condition and then pasteurization is unnecessary. Pasteurization is not a guard against filth, but only an unsatisfactory means of destroying the dis- ease germs which may chance to be in the milk from some source of accidental contamination. When young children must be fed upon cow’s milk probably the only safe procedure is to adopt home pasteurization or to use concentrated milk, unless one can afford the expense of purchasing high-grade certified milk. PRESERVATION OF EGGS 197 Ecos Eggs prove to be particularly difficult to preserve. They are sure to contain bacteria inside the shell, depos- ited there before the egg was laid. These will in time cause the egg to spoil. Eggs cannot be sterilized by heat, for this cooks them. Drying, of course, alters their nature. The use of low temperatures will preserve eggs as well as fruit. They may be protected from actual spoiling for some time by placing them in some liquids that keep away the air. Brine is used, and water glass is even more successful. To use the latter, mix the water glass purchased at the drug store with ten times its bulk of water, and keep the eggs in the mixture. They will remain in a usable condition for a long time, though they lose their fresh taste. No means are known by which this can be preserved. ErrecT oF BAcTERIA GROWTH UPON THE WHOLESOME- NESS OF Foop The question whether the growth of bacteria in the food necessarily renders it unwholesome remains yet to be considered. It is evident that after any food material has become completely putrefied it is quite ruined for all food purposes. The vile tastes and odors become so strong that no one can relish food that has entered the later stages of putrefaction. But how about the earlier stages, when the flavors and odors are so slight as to indicate that bacteria have only begun their action? In other words, are we liable to eat food which has begun 198 BACTERIA, YEASTS, AND MOLDS to be decomposed by bacteria, and if so, is such food unwholesome in any respect? We cannot regard any material as harmful simply because it is a product of decomposition or contains such. products. A number of such decomposition products are in more or less constant use. Aécohol is in a sense a decomposition product of yeast. It certainly is used to a very large extent, and probably, when used only in small quantity, causes no very considerable injury. Vinegar is also a decomposition product of bacteria, and is used freely by the human race without injury. The flavors of our high-priced butter are due to bacteria, and the extremely valuable flavors of cheeses are due, in many cases and perhaps in all, to decomposition products devel- oped in the curd of milk by the action of certain micro- organisms. Sauerkraut is a preparation which is allowed to undergo an incipient decomposition the flavors of which give the peculiar character to this food, That sauerkraut is a harmless food product is, of course, perfectly evident. In the general class of flavors known as gamzy we have fla- vors of decomposition produced by microérganisms. The very common use of such partially decomposed meats, and the fact that many persons are exceptionally fond of them, are indications enough that they are not appreciably harm- ful. These illustrations are sufficient to show that the simple fact that food contains decomposition products is not sufficient to make it unwholesome, since many decomposition products are distinctly desirable in our foods. The flavors of cheese in particular are very use- ful, for when eaten with coarse bread they give relish to otherwise rather tasteless foods. PTOMAINE POISONING 199 BAcTERIAL Poisons In Foops But, on the other hand, there are unquestionably some such products which are harmful and which, even though present in small quantity, may be decidedly harmful, or even poisonous. When certain kinds of microdérganisms grow in food material they give rise to a class of decom- position products which have been known under the gen- eral name of ptomaines. These ptomaines are chemical bodies of great complexity with whose chemical nature we are not in this work concerned. It is sufficient for our purpose to know that they are usually the result of bac- teria growing in animal products, and, while some of them are quite harmless, others are of an intensely poisonous nature. If such bodies develop in food they may render it unwholesome, or even fatally poisonous. To such poison- ous decomposition products are due instances of poison- ing from eating cheese, quite a number of which are on record. A similar cause explains the still larger number of cases of zce-cream poisoning, when many people have been rendered seriously and even fatally sick by the eat- ing of ice cream. Similar effects have sometimes resulted from the use of m/s, although such cases are rare. Many cases of poisoning are recorded from the use of meats, fish, and sometimes other foods. The poisoning in all such cases must not be confused with diseases produced by bacteria. Sometimes food may contain disease germs, and these may enter the body when the food is swallowed, and by growing inside of our bodies produce disease. (See Chapter XIV.) But in cases of poisoning from eating food the bacteria grow simply zz 200 BACTERIA, YEASTS, AND MOLDS the food. They do not live in the body, nor do they pro- duce any definite bacterial disease. The effects are due simply to the products of decomposition which have been developed in the foods by certain kinds of bacteria. These troubles are much more common than we are apt to realize. Since bacteria grow best at high temperatures, it is not surprising to find more,cases of food poisoning in warm weather. It is not an infrequent occurrence to have a general poisoning follow any one of the innumerable banquets held in our communities. Hundreds of cases of intestinal trouble occasionally follow such banquets. The illnesses resulting are rarely serious, but temporarily they produce great inconvenience and trouble. They are due to the development of ptomaines in some food prod- ucts, since almost any of the putrescible foods which come upon our tables may, in warm weather and under certain circumstances, undergo a type of putrefaction which gives rise to these poisonous ptomaines. When this occurs pto- maine poisoning is quite likely to follow the use of the foods. Such ptomaines are known to be developed quite readily in materials that have been preserved in cold stor- age and then removed to warm rooms. Hence it is desir- able to consume cold-storage material as soon as possible. It is almost certain that a large part of the szmmer diarrhea so common in warm weather is due to poison- ous decomposition products developed in some of our foods, milk being particularly likely to cause such trouble. Unfortunately we know very little concerning the con- ditions under which such poisonous materials appear. Not all bacteria produce them, and it is only rarely that food is thus rendered unwholesome by bacteria. We PTOMAINE POISONING 201 know that strictly fresh foods never contain these poisons. We know that their development is dependent in a measure upon temperature, inasmuch as they do not develop in food that is kept cool. We know that decomposition products are more likely to give rise to poisonous ptomaines in the absence of oxygen than in its presence. We know, lastly, that injurious substances are produced by bacteria; but we do not yet know the source of the bacteria, nor have we, for this reason, discovered any methods for keeping them from our foods other than those ordinarily adopted for checking bacterial growth. Anything that will pre- vent bacteria from growing will prevent ptomaine poison- ing. Consequently low temperature, drying of foods, and the other devices already suggested are the only means we have for guarding ourselves from such troubles. We may wisely remember that ptomaine poisoning is most likely to occur in foods that have been kept for some time in a moderately warm temperature. Fresh foods never contain poisonous ptomaines. The use of fresh foods and the preservation at low tem- peratures of any food that must be kept for some time are the only rules that can be given at present for prevent- ing such instances of poisoning. Eat food fresh when possible; keep it cold if it must be preserved; do not keep it any longer than necessary, and be particularly careful to consume quickly any material taken from cold storage. When food begins to have the smell of decom- position, it becomes suspicious, although this does not mean that it is necessarily dangerous, since many of these decomposition products are quite harmless. The food product that seems to give the largest amount of trouble is 202 BACTERIA, YEASTS, AND MOLDS ice cream, and it is therefore desirable to be particularly on one’s guard against its use in warm weather and, if possible, to use only that which has been made from fresh materials. Since the dangers are greatest in summer we should be particularly careful at this season not to allow any putrescible food to be warmed by the sun or by standing near a stove. CHAPTER XIV DISEASE BACTERIA The bacteria hitherto studied are all saprophytes. There remain for consideration those that can carry on their life within the body of living animals and plants, namely, the parasites. The distinction between parasites and sapro- phytes is not a sharp one, for while some species can live only in lifeless material, and others only in living material, there are many that can live either a parasitic or sapro- phytic life. When the bacteria grow in the body of a living animal or plant, they may give rise to disease, and these parasitic bacteria are therefore called disease germs, pathogenic bacteria, disease bacteria, etc. How BAcTERIA PRODUCE DISEASE The parasitic bacteria are all capable of growing and multiplying in the body, but the habits of different species of disease bacteria are widely different. Sometimes they become distributed all over the body, developing rapidly in any part, perhaps even in the blood. In such cases the disease produced by them is not located at any particular point, but distributed all through the body. This is true of certain forms of so-called blood poisoning, or septicemia. On the other hand, it sometimes happens that the micro- organisms become located in very definite parts of the 203 204 BACTERIA, YEASTS, AND MOLDS body, and while able to grow in certain places are unable to grow elsewhere. In these cases the disease produced may be local, although secondary general symptoms may appear, as is true of diphtheria. Between these two extremes are many intermediate types. Whenever bacteria obtain a foothold in the body they multiply more or less rapidly, and have the same general power of forming decomposition products and secretions as they have when growing in lifeless food. These new substances arising in the body are as varied in nature as are those produced by the common saprophytes. Among them are almost sure to be some that are distinctly poi- sonous, which we call ¢oxzns. These toxins may be either decomposition products or bacterial secretions ; but how- ever they are produced they are liable to be absorbed by the blood, and the body may thus be directly poi- soned by them. If the bacteria are in the blood itself, this poisoning is easy to understand; but localized dis- eases are similarly explained. Diphtheria, for example, is produced by bacteria growing on the inside surface in the throat. The bacteria themselvés do not enter the body, but their excretions are absorbed rapidly enough. Grow- _. ing in the throat, the bacteria develop very powerful toxins, and these are absorbed from the throat into the blood, producing a general poisoning of the whole body. Sometimes the germs grow in the intestine (Aszatze chol- eva), and their poisonous secretions are absorbed with the digested food. Something similar is true of practically all disease germs. All produce poisonous materials which are absorbed by the body, and these cause the direct injury characteristic of the various diseases. DISEASES, HOW PRODUCED 205 Not all the bacteria which secrete poisons are disease germs. Some saprophytes may produce deadly poisons, but since they are not able to grow in the living body they are never in a proper sense the causes of disease. They might, however, grow in our food and render that poisonous, so that if it were subsequently eaten it would give rise to cases of food poisoning such as already noticed. Such troubles are cases of toxic poisoning but not true diseases. A true germ disease is caused by the germs themselves entering and multiplying within the body. When the poisons and not the bacteria are absorbed by the body, the sickness comes on very quickly and violently, —a few hours after the poisonous food is consumed. But it is also of short duration, for, if the amount of poison absorbed is not sufficient to produce death, it is quickly excreted from the body, and a day or two afterward the person will have perfectly recovered, except for the weakening effects of the poisoning. This is the general history of-cases of poisoning from ice cream, etc. A true disease acts very differently. It is slow in appearing, gradual in its development, and very slow in disappearing. ‘The Course of Bacterial Diseases. The diseases pro- duced by bacteria have different histories in the body ; but a considerable number of them, with many of which the housewife is intimately concerned, have a course some- what as follows. For some days after the bacteria enter the body they have difficulty in maintaining a foothold. Sometimes, indeed, even though they succeed in entering, they are driven out by resisting powers which the body possesses but which we cannot here particularly consider. 206 BACTERIA, YEASTS, AND MOLDS If, however, they overcome these resisting forces and gain a foothold, they then begin to develop, so that in the course of a few days they become quite numerous. As they grow they produce their toxins, and these, devel- oped at first in small quantity, are absorbed by the body and give rise to the first slight symptoms characteristic of the particular disease. But the bacteria continue to multiply and produce their poisons in greater and greater abundance. As a natural consequence the body becomes more and more influenced by them, the symptoms of the disease become more and more violent, the person becomes more and more ill. This continues until death occurs or a crisis is reached. After the crisis the bacteria begin to disappear, and are finally driven from the body, while the poisons they produced become less capable of causing injury and are eventually excreted. The person may then recover entirely from the attack. RESISTANCE AGAINST DISEASE In most cases the body in driving off the bacteria acquires the power of guarding itself from a second attack of the same species, and the individual, for a time at least, is not liable to a second attack of the same disease. The whole explanation of how the body protects itself, drives off the invading bacteria, counteracts their toxins, and retains this power of protection in the future, is one of the interesting problems upon which bacteriologists are still studying. We cannot here enter into the subject, but it is well to remember that a recovery from common con- tagious diseases, like smallpox, scarlet fever, measles, mumps, DISEASE BACTERIA 207 whooping cough, typhoid fever, diphtheria, grippe, tonsilitis, etc., protects the individual for a time from a second attack. The protection lasts much longer in some cases than in others, and whereas the protection against the diseases at the beginning of the above list lasts for years or for life, the protection against those at the end of the list lasts for only a few months or weeks. Two important facts in regard to the resistance against disease must be mentioned. The ability of a person to resist an attack of any kind of disease germ is dependent upon two things. 1. The vigor of the bacteria. It has been learned by experience that the bacteria reproducing any definite dis- eases are more vigorous at some seasons than at others. A very vigorous lot of bacteria will give rise to a more serious attack of the disease, and will be more difficult to drive out than a lot of the same kind of bacteria that have been weakened by some unknown conditions. It is a well-known fact that some epidemics of smallpox, measles, etc., are milder than others; not simply because fewer people are attacked, but because those who are sick have the disease in a milder form. This difference in the severity of the attack is due in part to a difference in the vigor and activity of the bacteria that make entrance into the body, and is a matter beyond our control. 2. The vigor of the body itself. A vigorous, healthy, active body has a power of resistance sufficient to drive off most kinds of these invading parasites. If, however, the body is less vigorous, less active, i.e. in a low state of physical health, its resisting power is less and the body has great difficulty in driving off the invaders. This resisting 208 BACTERIA, YEASTS, AND MOLDS power, then, depends upon the vigor of the physical health. Hence it is of the greatest practical importance for every one to remember that robust physical health is the best protection against many types of disease due to the invasion of bacteria. It is true that persons in appar- ently perfect health may take these diseases, but it is never- theless the rule that the stronger the physical vigor the less is the likelihood of being attacked. At any rate a person of strong constitution will have a milder attack of the disease than one whose physical activity is weakened. DISTRIBUTION OF CONTAGIOUS DISEASES While these problems are of the utmost importance in every household, hygiene does not properly belong to the study of bacteria. There is one phase of the subject of bacterial diseases, however, that is of vital interest to every housewife. If contagious diseases are due to the growth of bacteria or other microdrganisms, it is clear that they may be avoided if we can prevent the disease germs from reaching the healthy individual. We have already noticed how one bit of decaying fruit contaminates another, the spores passing to the perfect fruit and caus- ing that also to decay. We have seen how the minute spores of molds and yeasts are.scattered through the air and blown about by the winds until they are almost sure to be found everywhere. We have noticed, also, how readily bacteria are distributed, and how surely the air of our houses is filled with them. We have learned that these microdrganisms are so abundant in the air that they are sure to get into any exposed bit of food, and we have DISTRIBUTION OF CONTAGIOUS DISEASES 209 seen that one of the housewife’s duties is to protect her food from their action. Very similar but more serious problems arise in the household in connection with the distribution of disease germs. If a disease is produeed only by the development of bacteria, of course it may be prevented if we can discover some means of keeping the disease bacteria from the body. In canning fruit the housewife tries to prevent bacteria from reaching it. Can she not by a similar principle protect her children from contagious diseases? This problem is the one feature of contagious diseases that belongs primarily to the housewife. The pre- vention of the distribution of such diseases is a subject which the physician can handle only indirectly, because it depends upon conditions in the home which he can- not control. The modern trained nurse may be able to do this; but in the majority of cases the whole problem of the prevention of the distribution of contagious dis- eases from individual to individual must rest upon the home maker. The doctor comes in for a few moments only, the nurse is only occasionally at hand, and the duty of protecting the inmates of the home from disease must fall upon the one who is at the head of it. To do it she must proceed according to the same principles by which she protects her food from decay. As she is obliged to use devices to keep bacteria away from all putrescible food materials, and as she must keep decaying apples away from the perfect ones, so it is her duty to guard the mem- bers of her family from the invasion of the disease germs. In her battle against disease the housewife should remember three things. 210 BACTERIA, YEASTS, AND MOLDS 1. The causes of these diseases are veal things and not simply matters of imagination. They can be seen with the microscope; they feed; they grow and multiply like larger animals and plants. Contagious diseases are not mere nervous affections that may be banished by forget- ting them and believing in their nonexistence. They are produced by definitely known living beings, and can be avoided only by keeping our bodies free from them. 2. The causes of the diseases in question are always microscopic, and can never be detected by the naked eye. Material which cannot be seen may therefore be filled with microscopic parasites which are capable of producing fatal diseases. An invisible particle of dust may harbor numbers of deadly germs ready to invade the living body and produce trouble. Since the foes cannot be seen, the battle is a blind and therefore a difficult one. 3. These agents are alive; they grow and multiply. Thus it follows that infectious material may rapidly increase in quantity. A particle of dust containing only a few parasitic bacteria may be the starting point of a disease which may spread widely until it shall become an epidemic with its scores of victims. The problem to be dealt with is something like that of fire. The flame of a single match is very slight and may do little injury; but this same flame may start a conflagration that will burn an entire city. So with the disease bacteria. Each of them, although extremely minute, is capable of develop- ing with wonderful rapidity, and a single one may develop sufficiently in the course of a few days to be scattered far and wide, causing a great epidemic. The extreme minuteness of these foes and their wonderful power of DISTRIBUTION OF CONTAGIOUS DISEASES 211 multiplying are the most prominent facts to be borne in mind when contending with contagious diseases. We must not, therefore, think that anything is safe from contamination with bacteria because it looks clean. The eye may not see the contamination even when it is present. Clear, sparkling water may sometimes contain deadly bac- teria, while dirty water may be perfectly safe to drink. Nor must we think any substance safe because it has only an extremely small quantity of infectious material upon it, for bacteria can grow so rapidly that a half dozen may become millions in a few hours if they have a chance to feed and grow. CHAPTER XV PREVENTION OF DISTRIBUTION OF CONTAGIOUS DISEASES What are the diseases against which the housewife must be on her guard lest they distribute themselves through her home? They are evidently those due to microscopic parasites, either bacteria or other forms of living things. Not all forms of sickness are due to parasites, for some have an entirely different cause. But the diseases with which we are here concerning ourselves —the so-called contagious diseases, which are well known to be “ catch- ing’’ and which pass from the patient to a healthy indi- vidual —are due to parasites. The chief of these diseases are smallpox, scarlet fever, diphtheria, measles, mumps, whooping cough, tonstlitis, and influenza or grippe,—all known to be contagious. In addi- tion there are other diseases, serious but much less con- tagious; so slightly contagious, indeed, that until quite recently they have not been looked upon as being capable of passing from individual to individual. The most prom- inent and important are typhoid fever and tuberculosis, The best-known form of the latter disease is commonly known by the name of consumption. Formerly neither typhoid fever nor consumption was supposed to be con- tagious, but it is now known that under some conditions they pass from patient to healthy individual. Lastly may be mentioned a class of diseases not in any proper 212 CONDITIONS OF CONTAGION 213 sense contagious but produced by parasitic organisms which may under peculiar conditions pass from individ- ual to individual. Most prominent among this last class is malaria, a disease never known to pass directly from one person to another but which may be distributed from individual to individual through an agency to be noticed presently. It must not be assumed that science at the present time knows the cause of all the diseases here listed. Some of them, like measles, scarlet fever, whoop- ing cough, and mumps, while almost certainly caused by microérganisms living in the human body, have not yet been satisfactorily explained, and we do not know the actual germs which cause them. There are some other contagious diseases besides those mentioned, for almost any trouble that produces open sores anywhere on or in the body is liable to be distributed from person to person. Those mentioned are, however, the most important. CONDITIONS OF CONTAGION To make it possible for a disease to pass from one person to another, three conditions must be fulfilled: (1) The microérganisms which produce the disease must find some means of exit from the patient. (2) The organisms must in some way be carried from the patient to the healthy indi- vidual. (3) The organisms must find some means of enter- ing the body of the healthy individual. If the parasites can meet these three conditions, the disease will be carried from patient to well person, and thus will be contagious. For a proper understanding, therefore, of the way to han- dle contagious diseases in the home.we need to consider 214 BACTERIA, YEASTS, AND MOLDS these three factors. If we know how the bacteria leave the body of the patient, how they are distributed, and how they enter the body of another, we are well equipped to guard against them. 1. The Means of Elimination from the Body A knowledge of the means by which the contagious material leaves the body of the patient is of first impor- tance in preventing the distribution of such material, and should always be the first question asked. There are several different methods. The parasites that produce certain diseases do not find any direct means of being eliminated from the body, and when this is the case the disease is not in any proper sense contagious. Malaria is the best example of this class of diseases, and yellow fever is probably a second. Malaria, chills and fever, or fever and ague, are all the same disease, and are produced by a microscopic parasite living in the human blood. Growing there, it develops poisonous secretions, and these acting upon the body give rise to the symptom of chill followed by fever only too well known in this disease. The parasite is a minute little body (Fig. 69, 1) which enters the blood corpuscle. Inside this corpuscle it grows, and finally breaks up into many lit- tle bodies, or spores. As soon as the spores are formed the blood corpuscle breaks to pieces, setting the-spores free and at the same time liberating the secreted poisons. These poisons cause the chill followed by fever well known in malaria. The spores may then enter into other blood corpuscles and go through the same history again MALARIAL PARASITES 215 (Fig. 69, 1-7). It takes about forty-eight hours for them to complete their history, and hence the chills, in the common form of malaria, occur every other day. One Fic. 69. Malarial organism. 2-7 show the stages that occur in ordinary blood, 7 representing the spores which appear after the blood corpuscle breaks to pieces. These spores are like 2 and immediately enter into fresh corpuscles, as at 3. 8 shows a so-called crescent body in the corpuscle. The crescent bodies become the sexual bodies, 9 and 92, which develop in the mosquito. 1o shows the union of the female sex body, 9, with one of the flagella of ga. 11-15 show the development of the united mass, 10, in the body of the mosquito, finally producing spores such as shown at 1. 16, the intestine of the mosquito, showing the malarial organism attached. form of the parasites, however, requires three days to com- plete the cycle. The malarial parasites remain in the blood and never pass out of the body by any of the ordinary excretions. There is therefore no direct means by which 216 BACTERIA, YEASTS, AND MOLDS they can pass from one person to another, and conse- quently malaria is not a contagious disease. This fact has been known for many years, and no instances of direct contagion have been noted. The last few years, however, have disclosed the fact that there is a means by which malaria is transmitted indi- rectly from man to man, and have shown us how the Fic. 70. a, the harmless mosquito (Cudex); 4, the malarial mosquito (Anopheles). a’ and a” show the position of the harmless mosquito when lighting on the floor or on the wall; 2’, 4” and 3’” show the position of Anopheles when lighting on the floor, wall, and ceiling. human body usually becomes infected with this disease. A certain kind of mosquito (Fig. 70, 6) forms an interme- diate connection between a malarial patient and another individual. This kind of mosquito may bite the patient, sucking into its body at the time a considerable quantity of blood. Inasmuch as the blood contains the malaria para- sites, the mosquito will become filled with them. The little organisms live in the mosquito as readily as they do in the MOSQUITOES AND MALARIA 217 human body, undergoing a different history, however. In the mosquito they pass through a new series of changes (Fig. 69, 8-15), finally lodging in the glands around the mouth (salivary glands). If this mosquito with its sali- vary glands thus loaded with these little parasites chances to bite another individual, thrusting its proboscis in through the skin, these parasites will pretty surely be forced into the body of that individual. When the mos- quito flies away it will leave the blood of the one bitten inoculated with the parasites. They are now in a loca- tion adapted to their life and they begin to develop. In a few days they are abundant enough to produce a poi- sonous effect upon their victim and he develops an attack of malaria. Thus this particular disease is transmitted from person to person by means of mosquitoes, and at the present time it seems as if most, and perhaps all, of the cases of malaria start originally from mosquito bites. Malaria is most prevalent at the seasons of the year when mosquitoes are abundant; it is most abundant in parts of the world where mosquitoes are most common; and it is most likely to be caught at night, the time when mosquitoes are the liveliest. It should be noted, however, that not all kinds of mos- quitoes are capable of carrying this malarial parasite. Fortunately the most common mosquito is quite free from them and is, therefore, not a source of danger. Only one group of mosquitoes is associated with this trouble. Fig. 70, 6, shows the common form of this species, and also the ordinary, harmless mosquito, a. The differences between them are shown in the figures. The most easily distinguished differences are the five delicate hairlike 218 BACTERIA, YEASTS, AND MOLDS feelers on the head of the dangerous species, rather than three, as in the harmless form (Fig. 70, a and 8), and the method of lighting with the body held in a straight line (Fig. 70, 6’, 6", 6"), rather than bent, as in the harmless spe- cies (Fig. 70, a’ and a’). It must also be remembered that not all mosquitoes, even of the harmful species, will be dan- gerous. Only those that have sucked the blood from mala- rial patients will contain the parasites and be able to transmit the disease. In other words, of all the mosquitoes that may bite us in summer only a few are likely to be infected and produce any trouble. We may be bitten thousands of times and still be free from malaria, while the next mosquito that bites us may inoculate us with these parasites. That family is the best protected against malaria that is the best protected against mosquitoes. If we live in a region where malaria abounds, it is somewhat dangerous to remain out of doors during the night, or even in the early part of the evening, unless properly protected. At this time mosquitoes are most likely to be flying about. From this fact arises the belief that night air is dangerous. It is not the night air that produces the trouble, but the mosquitoes in the air. It is also evident that the best method of protecting a household from malaria is by the use of mosquito netting. It is a curious fact that its use at our windows and doors is the best protection from these microscopic parasites, inasmuch as mosquito net- tings will keep mosquitoes from the houses and will reduce the chances of contagion. This is not a matter of theory only, for it has been found by careful observation and experi- ment that the simple procedure of covering doors and win- dows of houses with mosquito netting has produced a marked decrease in the amount of malaria in these dwellings. ELIMINATION OF GERMS FROM PATIENTS 219 It has been proved recently that yellow fever also is dis- tributed by mosquitoes rather than by direct personal con- tagion. The species of mosquito is different from either of those shown in Fig. 70, and lives only in warm climates. Mosquito netting is the best check for this disease. Yellow fever has been almost wholly stamped out of Havana by simply surrounding the patients with netting, thus pre- venting’ the mosquitoes from biting them and becoming infected with the germs which they might carry to other persons. It has also been banished from the Panama Canal zone by draining the swamps and closing up the breeding places of mosquitoes ; and the last time that yellow fever invaded the United States it was speedily crushed out as soon as active measures were taken to destroy mosquitoes and prevent their breeding. In all truly contagious diseases the parasites have some means of leaving the body of the patient. Their methods of exit are numerous, but are not very diff- Me cult to determine in the case of any particular yg ee disease. Most types of contagious diseases $ ea? ; have suggestive symptoms. For example, in, NS; ’ Ane smallpox, scarlet fever, or measles there is an cruption of the skin, and it becomes probable at once that this eruption is a means of elimi- nation of microérganisms. In diphtheria (Fig. 71) the germs grow in the mouth, clinging to the surfaces inside the mouth and throat, and it is quite evident that the breath, or at all events the forcible breath that comes with coughing, will detach the bacteria from their position in the throat and blow them into the air. In the case of whooping cough the violent paroxysms of coughing are probably a means of Fic. 71. Bacillus of diphtheria. 220 BACTERIA, YEASTS, AND MOLDS eliminating the infectious organisms. The same is true, probably, of tonsilitis and grippe (Fig. 72). In consump- tion, discharges from the lungs pass into the mouth and are voided in the sputum. It becomes evident, therefore, that here is a disease the contagion of which is found in the sputum and also in the breath exhaled when cough- ing. The ordinary breath does not contain the germs. rte In typhoid fever and cholera the most dis- 0 see tinctive characteristic of the disease is the Fic. 72. Ba- diarrheal discharges from the alimentary canal, cilluscausing and this suggests that the faeces may be the influenza or source of exit of infectious material. Thus, eae though contagious diseases differ very much from each other, it is rarely difficult to determine by observation the method by which the infectious matter leaves the body in the case of any particular contagious disease. The practical fact to bear in mind is that dur- ing the progress of an infectious disease any wzusual discharges from the body, mouth, skin, or elsewhere are almost always the means of exit of the parasites, and from such excretions all members of a household should be most carefully guarded. Special attention should be given to the care of the various discharges from the patient, and if this is done the contagion may be reduced very largely, and in many cases be absolutely prevented. 2. How Disease Germs are carried to and fro There are several methods by which infection may be carried from the body of the patient to that of the healthy person. In the case of some diseases it is chiefly HOW DISEASE GERMS ARE CARRIED 221 by direct contact. In such diseases as smallpox or scar- let fever, where the infectious material is probably on the skin, contact with the patient would be very likely to infect a healthy individual. Hence, with all diseases of this character, isolation is rightly considered of the greatest importance (see page 241). With most diseases, however, other means of transference are more common. The microdrganisms are not able to travel of their own accord, and are always carried about by some other agencies, the chief of which are the following. Insects. Insects are occasionally the means of carrying infectious material. The relation of the mosquito to malaria and yellow fever has been mentioned, Pi and jes have a very close relation to the dis- o RS tribution of typhoid fever. So close is this rela- 00 tion that it is now urged that the name zyphoid FIG. 73 Ba are cillus of bu- Jy should be used. Fleas, also, distribute the 4 .:. niseue: bubonic plague, which has recently produced so many deaths in the Old World (Fig. 73). It is quite possible that insects may carry the infection of cholera and some other diseases; but we know little upon these matters at present. We are thus taught to avoid flies, to shun mosquito bites and flea bites, and, in short, to avoid insects as much as possible. Mosquito netting has, there- fore, an actual sanitary value. Larger Animals. Occasionally larger animals transmit infectious microdrganisms. It is believed that diphtheria is sometimes carried from the patient in the sick room to another person by cats which wander about the house at will, The bubonic plague, which, fortunately, is as yet rare in this country but which is producing great ravages 222 BACTERIA, YEASTS, AND MOLDS in Europe, Asia, and Africa, is known to be transmitted by fleas carried by rats. Tuberculosis is sometimes transmitted by cattle, through their milk, to children drinking it. There may be other instances, not so well known, where larger animals are the means of distributing infectious material. Water. The distribution of disease germs by means of drinking water is chiefly confined to two diseases, typhoid fever and Asiatic cholera. Typhoid fever is very common and many epidemics are due to polluted drinking water. The disease is caused by a well-known bacillus (Fig. 74), and the method by which the water becomes contaminated is very easy to understand. The bacilli live in the intes- tines of the patient and are carried from him by the excreta. This material may be thrown = upon the soil or into earth closets, and is CO% : : 2 has liable in either case to percolate through esa the soil or be washed by rains into wells or Ties ue ee streams. Wells are filled with water that of typhoid fever. has soaked through the soil, and are quite readily contaminated with typhoid germs. Hence well water has been a very common source of the distribution of this disease. In most cities the excreta are thrown into sewers and the sewage may empty later intoa river. Hence the drinking water of cities may sometimes present very great danger. Cities frequently depend upon the water of running streams, and nearly all streams of any size in civilized communities are more or less contaminated by sewage from houses or towns on their banks. Such water will be likely occasionally to become infected with typhoid bacilli; so that rivers and streams are positive sources of danger to communities that depend upon them WATER AS A SOURCE OF DISEASE 223 for their drinking supplies. The result of drinking such contaminated water is the development of many cases of typhoid fever. A large part of the cases of this disease in cities are due to the contamination of drinking water. Many epidemics have been traced to just such a source. The Asiatic cholera bacillus (Fig. 75) has also in recent years been shown to be distributed by means of the water supply. The practical result of this discovery has been that, since cities have learned to guard their water sup- plies, severe epidemics of cholera have been prevented. This subject, however, need not detain us, as the disease is hardly known in America. S20 a But in the event of a cholera epidemic ya it should be remembered that the majority of cases are due to drinking water that has been contaminated with cholera bacilli. There are some other diseases occasionally distributed by water, but they are rare or little known. We need not consider them in our discussion. The practical question how to avoid such dangers must face the head of every household.. To answer this we must first fully realize that any water which has oppor- tunity for sewage contamination is dangerous for drink- ing, and cities supplied only with water directly from rivers or streams have a supply that is frequently unsafe for use. Those cities, however, which have large reser- voirs where the water stands for some time will have more reliable water, since the standing of water will in time always purify it of typhoid bacilli. The danger that the water supply may become a source of typhoid fever is, therefore, confined to those. cities that use the water of Fic.75. Bacillus of cholera. 224 BACTERIA, YEASTS, AND MOLDS” running streams, or those that pour their sewage into a lake and then pump the water out for drinking purposes. The housewife in the city cannot control her water supply. This must be left to health boards and water commissions. But she should learn whether the water is from a source liable to be contaminated with sewage. If so, she must regard it as dangerous and bestir herself to treat it in some way that will make it safe for drinking. This can be easily done by simply boiling the water, since even a brief boiling destroys typhoid bacteria. This is a satisfactory method of rendering such water harmless. After boiling, the water may be cooled with ice and used for drinking. _ Many households are supplied with various kinds of fil- ters attached to their faucets for the purpose of purifying the water. The ordinary filters ate worse than useless. They may make the water look clear and may remove some of the solid material ; but, while it looks pure, such water is no safer after filtering than before. Filters in ordinary use have xo value whatsoever in removing typhoid germs. They do remove large particles of dirt, but bac- teria pass through them as easily as dust through mos- quito netting ; and though they make the water clear they do not make it a whit less dangerous. One type of water filter (the Pasteur, the Berkefeld, and the Chamberland) is able to remove bacteria from water and thus remove all danger. Such a filter is shown in Fig. 76. The actual filter is a cylinder (Fig. 76, a) made of unbaked porcelain which is placed inside of a metal covering. The water enters the metal tube and is filtered through into the inside of the filter. These filters have FILTERING OF DRINKING WATER 225 been in use for several years and are quite efficient if prop- erly cared for. But in the ordinary home they are apt to be worse than useless, since bacteria lodge in the porcelain filter and grow there, so that the water passing through will be actually contaminated in filtering. To prevent this requires more careful attention than will generally be given in a house. The filtering cylinder should be removed every day and carefully cleaned by a thorough brushing, and about every fourth day it should be sterilized by boiling in water for five minutes. This kills the bacteria in the pores of the filter and renders ! it safe for a few days. Unless one | is willing to adopt this plan of regu- | lar sterilization of the filter, z¢ zs better not to use it at all. There L__4 is no other means in the household of filtering water which will remove from it the danger of distributing typhoid fever. There is a method yg 76, Pasteur filter, by which the water supply of a showing the filter itself, whole city may be purified by filter- “% made ab “unbaked : 7 porcelain, and the metal ing ona large scale; but this again (over, must be left to the public officials, and is not within the reach of the housewife. Her sole method of purifying suspicious water is by boiling. Aerated Waters. The recognition of danger connected with ordinary drinking water has led to the extension of the use of a variety of aévated waters, Apollinaris water, ari 226 BACTERIA, YEASTS, AND MOLDS Seltzer water, etc. Such beverages are not bacteria free, and a study of a large variety has shown that occasion. ally the number of bacteria they contain is considerable. Artificial aération, that is, charging the water with carbon dioxide, does not at once destroy germs, and if the water thus charged contained disease germs at the outset, the water is not rendered any safer than it was before aéra- tion. Such artificially prepared waters, therefore, are, while fresh, no safer than the original water from which they are made. After they have stood for a few weeks the disease germs seem to die and the water becomes wholesome. The zaturally aérated waters are, so far as known, never likely to be impregnated with disease germs. We may then conclude that naturally aérated water is safe from disease bacteria, and that other forms of aérated water are practically safe if they are not too fresh. In general, such waters are, therefore, more reliable than drinking water which has an opportunity for sewage contamination. Ice. The question has been raised in the last few years whether ice made from sewage-contaminated water is safe to use for cooling drinking water. Typhoid bacilli are not killed by freezing, and it has been claimed, therefore, that such ice is as dangerous as water. A more careful study of the subject has shown, however, that although the bacilli are not killed by simple freezing, they are mostly rendered harmless if they remain frozen in ice for several weeks. Ice harvested in the winter is therefore safe to use the following summer. This statement applies to clear ice, but not to snow ice sometimes found on the surface of -frozen ponds. MILK AS A DISTRIBUTER OF DISEASE 227 Milk. Milk is a means of distributing certain diseases ; not, indeed, a vehicle by which a contagious disease in a household is carried from one member of the family to another, but rather a source by which diseases from out- side may find entrance into the family. The diseases com- monly attributable to milk are not very numerous, four of them being very definite and two of a somewhat obscure type. The four definite diseases are tuberculosis, diph- theria, scarlet fever, and typhoid fever. Of the other two referred to, one is the indefinite series of intestinal troubles known as summer complaint, summer diarrhea, cholera infan- tum, etc., all characterized by the presence of diarrhea, and particularly common in warm weather ; the other is a type of fonsilitis, probably distributed in the same way. There is no doubt that all of these diseases are occa- sionally distributed by milk. The one most commonly attributed to this source is typhoid fever, and many instances have been recorded where epidemics of typhoid have been due directly to milk contaminated with typhoid- fever bacteria. Epidemics of diphtheria and scarlet fever have also been traced to the same source, though more rarely. The question whether any considerable amount of tuberculosis is attributable to milk has not been settled positively, but the probability seems to be that milk is a source of this disease, especially for young chil- dren. Pure milk, however, is never the cause of any of these troubles. Milk fresh from a healthy cow is never the source of any of the diseases above mentioned, nor indeed do any of them, except tuberculosis, come directly from the animal producing the milk. Some cows have tuberculosis and their milk may be dangerous ; 228 BACTERIA, YEASTS, AND MOLDS but cows probably do not have diphtheria, typhoid, or scarlet fever. Danger from these diseases lies in the pos- sibility that between the time of milking and the time when it reaches the consumer the milk may have been con- taminated with the bacteria which produce these troubles, and that these bacteria, growing in the milk, may render it a source of hidden danger. The relation of milk bacteria to the production of summer complaint and similar diseases is not so well understood. The only points that we need notice are: (1) Such troubles are doubtless due to the bacteria present in the milk. (2) They are consequently much more likely to be associated with milk in summer than in winter, since bacteria grow much faster in warm than in cold weather. (3) Fresh milk which has been kept cool is less liable to produce such troubles than older milk which has been kept warm, partly, no doubt, because the latter contains more bacteria than the former. Practically, then, the housewife should remember that old milk that has been kept warm is a source of danger, and that occasionally even fresh milk may be the cause of the diseases above mentioned unless some precautions can be adopted. How can precautions be taken in the household against these possible dangers? 1. We notice again that the milk that costs the most is the best and most reliable, while the cheapest milk is not only the poorest food but also the most dangerous. 2. Where it is possible to obtain information in regard to the character of the source of milk, the danger of contracting disease may be lessened. For in a small community knowledge concerning the man who delivers the milk should enable one to get some idea MILK AS A DISTRIBUTER OF DISEASE 229 as to whether he is careful or careless in handling it. In general it is well not to buy milk from a dirty or care- less milkman, for such a man is much more likely to sell milk that is a source of danger. For this reason milk distributed in glass bottles is more reliable than that distributed from metal cans. 3. Practically all of these dangers may be avoided by the use of pasteurized, con- centrated, or certified milk. The latter is a higher grade of milk, coming from special farms, and should have a certificate from a medical commission. It costs more than the ordinary grade, but is safe to use, and may be given to infants without fear of contagious diseases. In general, then, the first factor to. be considered in guard- ing the family from disease through milk is the obtaining of the supply from reliable sources only, even though the price may be higher. This will give a more reliable prod- uct, one that is more valuable as a food and less liable to produce disease. But in many households this may not be possible, and the family may be obliged to depend upon the ordinary milk supply without any knowledge of its source. What should be done under these circumstances? Such milk can be rendered harmless, so far as concerns the diseases referred to, by the processes of pasteurization mentioned on another page. Since milk from an unknown source may be rendered safe for use in this way, it is easy to under- stand why pasteurization has in recent years come to be so widely adopted. The same end is less satisfactorily reached by boiling. Every housekeeper will ask, however, whether such a precaution is necessary under ordinary conditions. This 230 BACTERIA, YEASTS, AND MOLDS general question cannot be answered and it will always bea matter for individual decision. That there is some danger is certain. Whether the danger is sufficient to warrant or demand the pasteurization of a// ordinary market milk is a matter of opinion upon which bacteriologists are not yet agreed. For young children who must be fed upon cow’s milk it is, under the conditions of modern life, not safe to use the ordinary milk supply. Many children are brought up on such milk without suffering materially therefrom ; but if it is uscd with young children there is considerable danger of the diseases mentioned, especially diarrheal troubles. In feeding young children, therefore, it is wise, and almost necessary, to adopt some method, preferably pasteurization, of destroying the disease germs that may be present. - If the milk is to be used by adults, the necessity is not so great, for adults are not as a rule so liable to diseases from this source. Nevertheless milk from the common milk supply, unless pasteurized, must be looked upon as a possible source of typhoid fever and some other troubles. It should be emphasized especially that milk is not necessarily harmless because it has not soured. It is true that soured milk contains more bacteria than sweet milk, but most of them are harmless, while a sample of milk that is perfectly sweet may contain disease bacteria and be unsafe to use. The Air. The readiness with which bacteria can float in the air suggests that they may be easily distributed by this means. The agency of air in distributing diseases has been somewhat overrated, but it occurs in a few dis- eases which we usually look upon as extremely contagious. Skin diseases, like measles, scarlet fever, and smallpox, are AIR AS A DISTRIBUTER OF DISEASE 231 distributed by the air, and a person can take them with- out coming in actual contact with the patient, when no other means of infection is known save that of air cur- rents. The distribution of disease bacteria by means of air, however, does not extend very far from the patient. If bacteria are thrown off into the air, a second person in the same room and in the immediate vicinity may become affected by them. But the danger is confined chiefly to the room occupied by the patient. It is true that the germs may pass into other rooms or out of doors, but they usually cease to be dangerous, partly because they become mixed with such large amounts of pure air, and partly because they soon settle to the floor or ground and are destroyed by sunlight. The danger of taking such diseases decreases rapidly as we pass from the immediate vicinity of the patient. The danger may be much decreased if the skin of the patient be kept moist by a mixture of glycerine and water, or by a little oil rubbed on the skin. This may be done in scarlet fever, during the later stage, when the skin is peeling, and the danger of contagion will thereby be lessened. From these facts we can conceive that the dust and dirt collecting on the floor of the sick room will be likely to become a source of trouble. The dust that accumu- lates on the floors, walls, or ceilings, on the window sills or the doors, or on any article of furniture in the room occu- pied by a patient, is likely to contain the living disease bacteria. Such material is therefore a source of con- tagion, and in protecting a family from attacks of conta- gious diseases the dust accumulations of the sick room must be looked upon as a special source of danger. 232 BACTERIA, YEASTS, AND MOLDS In a few diseases characterized by coughing the germs are distributed by air from the mouths of the patients. The most noticeable of these are consumption (Fig. 77), whoop- ing cough, and very likely measles at certain stages, The air coughed from the mouth in these cases contains small particles of moisture which float around for some time, and these particles are likely to be laden with disease germs. As long as this water is floating the air may be dangerous to another person breathing it. In these cases also the danger is practically confined to the immediate vicinity of the patients, for these particles of moisture do not float very long but soon sink to the ground or come in contact with the walls of the room. Danger is confined to within a few feet of the patient, a dis- tance as great as that of the next room being usually sufficient to free the air from such floating microdrganisms. The only way to avoid such dangers is to insist upon plenty of fresh air in the sick room, and to air the rest of the house frequently and thoroughly. Tuberculosis (Fig. 77), or consumption, has a special source of danger in the sputum of the patient. This material is filled with the dangerous bacilli. As long as it is kept moist they have little chance of distribution ; but if the sputum is voided on the floor or where it can dry, the dried material will blow around as dust, still contain- ing active bacilli. The sputum of consumptive patients should be received in old cloths which can be burned, thus destroying all danger, or in special cups which can be sterilized by disinfectants. Fic. 77. Bacillus of tuberculosis. DUST OF SCHOOLROOMS 233 It is extremely important, also, to remember the sig- nificance of dust in a schoolroom. A schoolroom with children from many homes is likely to be a collecting place of disease germs. The children frequently bring such germs to the schoolroom, where they are distrib- uted through the air, float around for a while, and even- tually settle on the floor. If they remained on the floor they would be harmless, but every time the room is swept or dusted the germs are stirred up again. Sweeping and dusting a schoolroom decidedly increases the danger of contagion. If feather dusters could be discarded and brooms also dispensed with, their places being taken by damp cloths, the amount of contagion would be materially reduced. If the floors, window sills, desks, and tables were wiped each day, the dust, instead of being scattered through the room, would be collected and removed by the damp cloth. The cloth should subsequently be rinsed and occasionally washed in hot water. Where this method has been adopted the results have been surprising. One school, for example, with over four hundred pupils, burned up the feather dusters and used damp cloths for cleaning. During the following year there was not a single case of contagious disease among the scholars, an altogether new experience for the school. The same general facts would apply equally well to the household. Brooms and dusters simply distribute germs through the air, and should be dispensed with as far as possible. Vacuum cleaners and damp cloths should, where possible, take the place of brooms and dusters. Woodwork should always be cleaned with a damp cloth rather than by dusting. No simple rule will be more useful in checking the distribution of contagious 234 BACTERIA, YEASTS, AND MOLDS diseases than that of discarding the old-fashioned method of dusting and replacing the same with the more sani- tary one of wiping. It is much better to have bacteria in the carpets, where they will die after a time, than to have them in the air that we breathe. Uncooked Food. Some of the foods that come upon our tables without cooking may be the means of distributing. disease. This is not, however, very common, and is men- tioned only as a possibility. If fruit has a chance to become contaminated with infectious material (such as sewage, or sewage-infected water, or consumptive sputum), and is eaten uncooked, the person eating it is in danger of contracting disease. The chance, however, of fruit becoming contaminated with disease germs is not very great, and we cannot therefore look upon it as a very serious source of danger in a household. Lettuce, celery, or radishes grown on sewage farms have a chance of contamination from typhoid germs in the sewage used for fertilizing the soil, and have becn pointed out as pos- sible dangers. Troubles from these sources are, however, rare and may be commonly neglected, but in times of epi- demics it is always wise to guard against even this pos- sible source of danger by avoiding the consumption of fruit or vegetables that have in any way whatever been exposed to a chance of contamination. Although it is thus seen that quite a number of our foods are sources of possible danger, it is not wise to be too fearful over the matter. The fact that certain dis- eases under certain conditions are caused by some of our commonly consumed foods must be admitted; but it must also be remembered that the chances in each case MEANS OF BACTERIAL INVASION 235 are small; that our fathers and grandfathers have con- sumed similar foods for generations and have suffered only occasionally therefrom. It is therefore wiser not to be over alarmed or to make life burdensome by too great precautions, but simply to use such care as may seem feasible and possible in our homes, and not give up the use of any desirable food because we know that it may be an occasional source of danger. Some people have actually given up the use of butter and milk because it has been shown that they contain so many bacteria. Such a procedure is sheer nonsense. The facts here outlined have been given, not for the purpose of inducing people to avoid the use of such materials, but merely to suggest to them the wisdom of adopting possible precautions against consuming contaminated foods. 3. Means of Invasion A matter of almost equal importance in considering the distribution of disease is the means by which the bacteria get into the body. Each species may have its own means of entering, and frequently each can find entrance in only one way. If it should get in by other means it would pro- duce no injury. Some species, however (tuberculosis), pro- duce trouble, no matter how or where they enter. If we know the means of entrance of any contagious material, we are of course in a much better position to guard our- selves against it. The important means of entrance are as follows. The Skin. Some diseases find entrance chiefly through the skin. This is true of the bacteria which cause the 236 many little BACTERIA, YEASTS, AND MOLDS sores, festers, boils, and abscesses, all of which are commonly due to bacteria entering through the skin (Fig. 78). These bacteria are harmless in the Lf stomach, and, indeed, we are swallowing them 7 my all the time. The mouth contains great num- s°v$ = bers of these bacteria, as well as numerous other species, but they do us no injury. Skin 3@ ne diseases like ringworm, dia etc., enter in ¢@ *et ** the sameway. This is likewise the case with ue lockjaw (Fig. 79), exysipelas (Fig. 78, 6), and pa various forms of blood poisoning, some of ge 7 which are of comparatively little importance, QL while others may be serious and fatal. It is Fic.78. Vari. Possibly also true of measles, scarlet fever, ous patho- and smallpox, although in these latter cases genic cocci. @, pus cocci; we have really no knowledge of the matter. But though these diseases enter through 6, cocci pro- ducing pneu- the skin, it should be remembered that the monia; ¢ surface of the body is commonly quite well erysipelas cocci. protected against the invasion of microérgan- isms. We have already seen that the skin of truits, if uninjured, protects the softer portion of the interior from decay to a considerable extent, and that the organisms which produce decay usually enter We through bruises, cracks, or cuts in the skin. Precisely the same thing is true, probably to an even greater extent, in the case of the human body. The outer layer of the skin isa protection which the bacteria cannot ordinarily Fic. 79. Bacillus of tetanus penetrate. If therefore the skin is unbroken and unin- jured, a person is almost perfectly protected against the INVASION THROUGH THE SKIN 237 invasion of the particular kinds of bacteria which pass in through the skin. A person whose skin is not broken can without danger handle infectious material which might pro- duce fatal results were the skin cut or bruised. It is, how- ever, hardly ever the case that a person’s skin is unbroken over his entire body. Cuts, bruises, and scratches break the skin, and through such openings microérganisms may find entrance into the body. A little sliver in the skin is frequently the starting point of a fester, a boil, or an abscess, or even of a severe and perhaps fatal case of blood poisoning. So small a thing as a pin prick may sometimes allow entrance to mischievous bacteria. The conclusion of all this is that a whole skin is a protection which can almost absolutely be relied upon; but a more important lesson is that any break in the skin should be more or less carefully protected. The almost surely fatal disease lockjaw (tetanus) comes from soil bacteria getting into the body through the skin, and is apt to occur in wounds made by rusty nails, etc., which have been lying a long time on the earth and have become contaminated with the lockjaw bacillus. All cuts and bruises should be carefully washed with boiled, i.e. steril- ized, water. The fear of bacteria explains why the sur- geon endeavors to clean the surfaces of wounds by some disinfectant which will prevent the growth of micro- organisms. Here, too, is the reason for protecting from further contamination a wound thus cleansed, by covering with bandage or plaster. All of these devices are for the purpose of protecting the body from the entrance of bac- teria, and make it possible for the wound to heal readily without the disturbance which would be produced if 238 BACTERIA, YEASTS, AND MOLDS bacteria got into the wound. Modern surgery is based on the simple plan of keeping bacteria out of wounds. The frequent efficacy of treating wounds by such crude meth- ods as covering them with tobacco juice or even mud is due to the fact that these act as mild antiseptics and protect wound surfaces from the entrance of dangerous organisms. The skin should therefore be carefully guarded, and in all cases of diseases connected with the skin, a list of which has been given above, special care should be taken that no part of the body which is cut or bruised or scratched, or has sores upon the surface, should be allowed to come in contact with infectious material. If this is done, the danger of contagion will be greatly reduced. Though a person with whole skin may safely handle infectious material, no matter how dangerous it is, one whose hands contain even the smallest pin scratch might contract contagion and suffer illness or death from such procedure. The Mouth. Some diseases find entrance through the mouth by means of the food or drink swallowed. They are chiefly typhoid fever, tuberculosis, diphtheria, and cholera, although there are some others. It is manifest that not only is the chance of contagion through the mouth less. than when a disease is borne by air currents and enters through the skin, but it is more easily prevented. The diseases mentioned are not usually regarded as very con- tagious, except inthecase of diphtheria, where thecontagion may be through food (milk) or air. To prevent contagion from most of these diseases it is only necessary to guard all that enters the mouth, keeping it free from infection. ENTRANCE OF BACTERIA THROUGH THE MOUTH 239 Food served hot is free from danger. Food and liquids should be specially guarded from contamination in the sick room, especially in cases of typhoid fever. The utensils used by the sick patient should never be used by other inmates of the house. Those who have anything to do with nursing the patient or handling soiled bedding should be especially careful that nothing has an oppor- tunity of getting into their mouths. Especial care is needed to guard school children in these respects, for their ignorance and thoughtlessness lead to many chances of contagion from mouth to mouth. Contagion in these diseases may be carried by the fingers; for if a person touches the patient he is likely to have his fingers con- taminated with infectious material, and should he subse- quently place his fingers in his mouth, infection would be very likely to follow. If one guards everything that goes into the mouth, the chance of infection is slight. It is a . significant fact that in cases of typhoid and cholera — the most typical diseases of this sort— nurses and doctors rarely take the disease from their patients. They have learned the method of infection, and guard themselves by keeping infectious material from their mouths. Breathing. Some diseases undoubtedly enter the body with the breath. Fortunately the diseases thus contracted are few. Foremost among them stands /uderculosis. Diphtheria is probably contracted in the same way, and possibly the grippe, whooping cough, and measées, although in regard to the last two we know almost nothing. There is no means of protecting ourselves against this method of infection except to keep away from individuals suffering from the diseases. As already mentioned, the bacteria 240 BACTERIA, YEASTS, AND “MOLDS that pass into the air fill the space in the immediate vicinity of the patient, but do not disseminate themselves to a very great distance. Hence persons near the patient are exposed to the disease by breathing the air, while those at some dis- tance are but slightly exposed, and those at a greater dis-. tance, not at all. The danger is mostly confined to the room in which the patient is kept, and hardly extends to the rest of the household. The only protection against this method of invasion, then, is to avoid the immediate vicinity of the patient, and to keep the air of the room and the rest of the house as fresh as possible. If one who is obliged to breathe such air will take the opportunity frequently to breathe fresh air out of doors, his danger will be reduced. Bacillus carriers. It frequently happens that persons who have had germ diseases continue for some time after recovery to carry around in their bodies the bacteria of the disease. Although the germs no longer do any harm to the recovered patient, they are still as dangerous as ever, if, by any chance, - they should reach another individual. Such persons are called “bacillus carriers,” and as long as they continue to harbor these disease germs they are a source of danger to their associates. Such bacillus carriers are particularly com- mon after cases of typhoid fever and diphtheria. Recovered typhoid patients have been known to carry active typhoid bacilli for many years. In one famous case such a person was employed as a cook, and for a period of twelve years cases of typhoid fever appeared in all families shortly after she was first employed by them as cook. Such bacillus car- riers in a dairy have also been known to infect the milk and produce a typhoid epidemic, distributed by the milk supply. Even more common is the distribution of diphtheria by BREATHING 241 carriers. While the diphtheria germs do not remain in the patient’s mouth for any such length of time as those of typhoid fever linger in the body, they do remain there from three to six weeks, and sometimes for some months. As long as they are present the person is a source of danger to his associates. A person may become a carrier of diphtheria germs who has not himself had the disease. It frequently happens in a school that after one or two cases of diphtheria have appeared, quite a number of the children will be found to have diphtheria germs in their throats, having obtained them, doubtless, from associating with the patients. To these carriers the bacilli may not be doing injury, since some children are immune; but as long as the germs are present in their mouths the carriers are a source of danger to others who may not be immune. The most efficient method of prevent- ing the distribution of this disease through a school, or any institution, is to examine the throats of all children who are associated with cases of true diphtheria, and then temporarily to isolate those whom a microscopic examination shows are carriers. By such means it is practically always possible to check the spread of diphtheria and to prevent epidemics in schools, and the method is more effective than that of closing the schools. CHAPTER XVI PRACTICAL SUGGESTIONS From the facts outlined it is very easy to draw certain practical suggestions for dealing with contagious diseases. Isolation. In the case of highly contagious skin diseases, such as scarlet fever, measles, smallpox, etc., the patient must be isolated from the rest of the household as com- pletely as possible. This should be done by confining him to one room and allowing no one to enter except those necessarily engaged in caring for him. The same general treatment may be applied in diseases characterized by coughing, like whooping cough and con- sumption. Diphtheria, also, though not distinctly a cough- ing disease, is distributed by breath that is forcibly exhaled by the patient, and the seriousness of the disease makes it necessary to adopt isolation. While it is manifest that the only means of absolutely avoiding contagion from tuberculosis and whooping cough is to isolate the patient, it is also clear that complete isolation of a sufferer from whooping cough or tuberculosis is rarely possible in an ordinary household. Diphtheria is such a serious disease, so rapidly fatal, and its course is usually so brief, that com- plete isolation is not only feasible but necessary. The other two diseases last so long that isolation is generally very burdensome, difficult, or impossible. It is well to remember that in such diseases periods of coughing are : 242 ISOLATION 243 the times when there is most chance of contagion, and that all well persons should, so far as possible, be kept away from the vicinity of these patients at the time of coughing. If this is done and the sputum is cared for, the chance of contagion is much reduced. The question often arises how long the isolation should be continued. One must usually depend upon the physi- cian or board of health for an answer to this question, since the period of isolation varies with different diseases. For scarlet fever it is about six weeks ; for whooping cough it is certainly as long ; for diphtheria the time of necessary isolation varies from two to six weeks, and a laboratory examination is necessary to determine when a convalescent patient ceases to be able to transmit the disease to other children. Measles is only contagious in its early stages, anda week after the patient “breaks out”’ is no longer communi- cable. In general, the period of isolation must be determined for each disease by the advice of physician or board of health. Excreta. In the case of diseases located in the alimen- tary canal, and distributed by excreta, isolation of the patient is not so necessary, but everything that comes in contact with the discharges from the alimentary canal should be carefully guarded. This will include not only the discharges from the intestine but also those from the mouth. All possible precautions should be taken to prevent any such material from being distributed through the household. Such diseases can very easily be confined to the patient and the sick room if care be taken with the excreta, if all soiled materials coming in contact with the patient be properly treated, and all eating utensils thoroughly disinfected. 244 BACTERIA, YEASTS, AND MOLDS Clothing and Bedding. Any articles of clothing that come in contact with a patient, any towels or cloths used in bathing him, are very likely to be mediums for the distribution of disease. If it is a skin disease, the clothing is sure to become infected. If the disease bac- teria are eliminated through the sputum or the excre- ment, it is almost inevitable that the clothing, especially the bedding, will be contaminated with infectious material. In all skin diseases, as well as in cases of typhoid, diph- theria, tuberculosis, and indeed most contagious diseases, clothing and bedding are sources of infection and must be guarded carefully. The clothing and bedding should not be sent to the general laundry but washed separately and thoroughly boiled. Nothing should be worn in the sick room by nurse or patient that cannot be washed, and all unwashable fabrics, curtains, carpets, etc., should be removed from the room where there is a contagious disease. Eating Utensils, etc. The eating utensils used by a patient, or indeed anything that he handles or uses dur- ing his sickness, may be very easily contaminated with the infectious material. It is perfectly evident that a diphtheria patient who has the bacilli in his mouth will contaminate the spoons, knives, and forks which he uses with the bacteria that are producing the trouble in his throat. The same thing would be true, though perhaps to a less extent, of all contagious diseases, for a patient cannot handle anything without danger of thus infecting it. Consequently all utensils from the sick room and all articles handled by the patient must be looked upon as means of distributing the disease. The practice of TREATMENT OF INFECTED ARTICLES 245 taking the spoons, knives, cups, and plates from which the patient has taken his meals, and carrying them into the kitchen to be washed with the other household uten- sils for subsequent use by the rest of the family, is a dan- gerous one and is one of the easiest and perhaps most common means of distributing the disease from the sick room to the rest of the household. Doubtless many times the distribution of diseases is attributable to the indiscrim- inate use of the same eating utensils by the family. It is easy to avoid this danger. (1) Allow no one to use the eating utensils which the patient has during his sickness. (2) After his recovery put them into boiling water and leave them for several minutes. Do not wash them with the eating utensils of the rest of the household. Thorough boiling will render them harmless, and there- fore even a knife or a spoon coming from the sick room should be placed in boiling water before it is used by any other person. It must be borne in mind that water that is simply hot is not sufficient for this purpose. The water must be doz/img, and it is better if the articles are placed in the water and the water boiled for five or ten minutes before they are taken out to be used. The state- ments made concerning eating utensils apply also to any articles handled by the patient. Books used by children recovering from diphtheria or scarlet fever and then returned to a public library may distribute disease through a community. In cities where the schools furnish supplies children should be cautioned against putting into their mouths pencils, etc., particularly those belonging to other children. If a person has a scalp disease, like ringworm, he should not be allowed to use 246 BACTERIA, YEASTS, AND MOLDS combs or brushes used by other members of the family, for other cases of the disease would be sure to follow. Nurses. Those who nurse the patient should take special care in a number of directions. They should have a change of clothing to put on when they leave the sick room to mingle with the rest in the house; they should wash’ their hands frequently with some disin- fectant to be mentioned later, especially after handling the patient, his bedding or his clothes. They should be especially careful to avoid putting their fingers into their mouths, for in many diseases this is a common means of infection. A nurse who carefully observes. these precau- tions is much less liable to infection from any of the diseases. The face also requires frequent washing. The hair is a particularly good lodging place for bacteria, and a good nurse wears a cap to protect her head in cases of contagious diseases. Treatment of theSick Room. After the recovery of the patient it is necessary that the room he has occupied should be thoroughly disinfected before any other mem- bers of the household are allowed to enter it. The method of disinfection will be found in another place. We will here only emphasize the fact that in order to prevent the appearance of other cases of the disease such disinfection is absolutely necessary before the room is occupied by other people. : The treatment after recovery from a contagious disease is sometimes difficult to determine. So far as concerns the patient himself, the proper procedure after recovery is to bathe himself thoroughly in a disinfectant solution suitable for this purpose, the disinfection or bathing SEWAGE 247 including the hair as well as the rest of the body. The person should be given clean clothes that have not only been thoroughly washed but disinfected by proper means ; after which there is no danger of his transmitting the disease, to others. Sewage. Since the discharges from patients find their way into sewage, this material is extremely dangerous, indeed from the standpoint of human health one of the most dangerous of all substances. Every effort should be made in the household to guard against it. Par- ticular attention should be given to keeping the drinking- water supply from becoming contaminated with sewage. In cases where the water is from a well there should be especial precautions against contamination from privies or sewage. The health of the family depends upon having the well a long distance from sewage and privies. In cities the sewage empties commonly into one gen- eral system, and most of the houses are connected by a series of underground channels. These sewers carry the discharges from all the patients in the city, and hence contain the dangerous disease germs. Since each house is connected with this system of sewerage, it is of the greatest importance in modern cities that the connections with the sewer pipes should be most carefully guarded. Proper plumbing does this satisfactorily, but it is neces- sary that the plumbing should be thorough and that it should occasionally be inspected. All bowls, sinks, and closets should be connected with the sewer by traps. The general design of such a trap is shown in Fig. 80. Between the bowl or sink and the sewer is a bent tube filled with water. As long as this trap is thoroughly 248 BACTERIA, YEASTS, AND MOLDS filled with water no bacteria and no gas can pass from the sewer into the sink. If the joints of the sewer pipes are tight and the traps are full of water, there is no dan- ger that anything from the sewage can come into the rooms. The traps, however, occasionally get emptied of water, and then gases may pass up from the sewers. Moreover, the insides of these traps become breeding places for certain kinds of bacteria, though rarely d'sease bacteria, and may in time become full of them. It is therefore de- sirable to pour some kind of disinfectant occasionally into the bowls and sinks. A weak solution of carbolic acid, one part to twenty, or a solution of chloride of lime, one part to twelve, put into bowls and Fy, go, Diagram showing the sinks will disinfect the traps. principle of two kinds of traps It is also an excellent plan to %¢P4tating washbowls from pour boiling water frequently asa down sinks, bowls, and closets, for this not only helps to clean but helps also to disinfect. A worse danger to a household are /aky sewer pipes. If these are poorly laid, the contents of the sewer may ooze out into the cellar or soil under the cellar and become a source of considerable danger. Leaking sewer pipes in a house are a serious menace. The evils from sewer gas have, however, been overrated. Sewer gas itself is not capable of producing any specific disease. IMMUNITY 249 If it is constantly escaping into a house, the members of the family may perhaps become weakened by continually breathing such gas, but it is doubtful whether they would be more liable to the attack of parasitic diseases. Such persons might perhaps have a tendency to throat troubles, but there is no evidence in our possession that sewer gas can cause any particular disease. The diseases are caused not by gases but by living bacteria, and while sewer gas may be deleterious in its weakening action upon individuals breathing it, it can never produce disease. Protection following Cure; Immunity. The recovery from a contagious disease, as a rule, protects the indi- vidual more or less perfectly from a second attack of the same disease. But the amount of protection differs with different diseases. After recovery from some of our contagious diseases, like scarlet fever, a person rarely has a second attack during life. With other diseases a second attack is more likely to follow, but in all cases there is at least a temporary protection following the recovery. In other words, after a person has recovered from a contagious disease he is not, at least for some time, liable to the same disease again. This protection lasts in some cases for many years and perhaps through life (scarlet fever); in other cases it may last only a few years (measles?); in some cases perhaps only a few months or weeks (diphtheria); but a temporary protec- tion is always gained. The reason why one is thus pro- tected from a.second attack scientists have not yet wholly explained. Vaccination. A word must be given in regard to the method of protecting the body against smallpox known 250 BACTERIA, YEASTS, AND MOLDS as vaccination. This method has been in use over a hundred years, but there is a vast deal of misunderstand- ing in regard to it. The fact of the case is that vaccination gives to the individual a certain amount of protection against the dreaded and frequently fatal dis- ease, the protection being due to about the same cause as that which produces the immunity following recovery from germ diseases. The protection is not an absolute one, since vaccinated persons do occasionally take the disease. But for a time after vaccination one is almost surely protected against smallpox. How long this protec- tion may last no one knows. It certainly does not last forever, and if one wishes to remain immune it is neces- sary to repeat the vaccination occasionally. For a year or two after vaccination the protection is strong and nearly absolute. But after a couple of years it gradually becomes reduced, and after ten or fifteen years the amount of protection afforded is very slight. The proper method, therefore, of guarding against smallpox is vaccination in childhood, followed by vaccination some years later, and perhaps again at intervals in later life. Experience has shown over and over again that proper attention to vacci- nation will check smallpox epidemics, and no other means has hitherto been satisfactory. It must be recognized, however, that vaccination is not always harmless. In the vast majority of cases the per- son suffers nothing except a very trifling inconvenience from the treatment. In extremely rare cases, perhaps, more serious results arise. If these secondary troubles do occur, they are usually not due directly to the vaccina- tion but to the vaccination wound becoming contaminatéd VACCINATION 251 with bacteria. It is therefore necessary to protect the wound carefully against possible contamination. This is done by the physician in various ways. Although there is thus some danger in vaccination, the chances of trouble are very slight indeed, whereas the protection afforded against smallpox is so great as to lead scientific men and physicians to recommend its use unhesitatingly as a general protection against this extremely violent and frequently fatal disease. Modern physicians have means of almost perfectly protecting the members of the household from the con- tagion of diphtheria by means of the product known as diphtheria antitoxin. Where a family is unable to isolate a patient from other children, an injection of antitoxin is almost certain to prevent the distribution of the disease. Its use is being adopted very widely by physicians, and every housewife should understand that it is a precaution- ary measure that is eminently wise, perfectly safe, and the only known means of protecting a family where complete isolation of a diphtheria patient is impossible. Many phy- sicians, indeed, adopt it as a precautionary measure in households where there are several children, even though the patient is isolated. A method of vaccinating against typhoid fever has also been devised, and is coming to be extensively used. The treatment is perfectly harmless, and it gives a very high degree of protection against the disease. It is so efficient that it is made a requirement now in the United States Army for all soldiers who are to camp in places where they are exposed to typhoid. 252 BACTERIA, YEASTS, AND MOLDS PHYSICAL VIGOR A PROTECTION AGAINST CONTAGION The best protection against contagion is robust health. A person in strong, vigorous health is much less liable to yield to disease than one less robust. Consequently in the attempt to protect the household from: contagious diseases special emphasis should be placed upon methods, of increasing the physical vigor of its members. This can be done by wholesome food, by exercise, and by fresh air. An active body is far less liable to disease than one more or less passive, and vigorous exercise in the open air, accompanied by plenty of wholesome but not too rich food, will be the most thorough safeguard an individual can have against the attack of some infectious diseases, especially tuberculosis. The need of fresh air should be emphasized, perhaps, more than any other point, for the air in houses, for reasons already indicated, is much more liable to be filled with infectious material than the out- door air, and a person who constantly remains in the house is much more liable to yield to contagion. If, however, he is careful to exercise in the open air, he will ward off attacks to which otherwise he might yield. This applies even more forcibly to the air of our sleeping rooms than to that of our living rooms, for fresh air in the sleeping room is one of the greatest desiderata in maintaining good health. The belief that night air is injurious is responsible for much ill health. Sleeping in close rooms without sufficient air causes a general lower- ing of bodily vigor. Our sleeping rooms should have the windows open even in cold weather, and, provided there be mosquito nettings at the windows to keep out GENERAL CONCLUSIONS 253 insects, there is absolutely nothing to be feared in night air. While vigorous health is a protection against some diseases (tuberculosis), it is far less efficient against others (smallpox). It should always be borne in mind that contagious diseases are real things, and not the result of imagination. They are produced in our bodies by the growth of certain microscopic animals and plants in our blood, muscles, or elsewhere. They cannot be warded off by simply disbe- lieving in their existence, and the sooner the housewife learns that a contagious disease is due to distinct living beings which are transported from one person to another and live as parasites in the patient, the sooner will she be in a position to protect her family from the spread of contagion. GENERAL CONCLUSIONS Each type of infectious disease must be fought in its ownway. The so-called children’s diseascs are so decidedly contagious that isolation alone is capable of preventing their distribution. Of the adult diseases, however, the most serious may be largely checked by proper means. Smallpox must be fought with vaccination and isolation, diphtheria by antitoxin and isolation, typhoid fever by a guard placed over the water and the milk supplies and by fighting flies, malaria by destroying the breeding places of mosquitoes and protecting the body from mosquito bites. Of all diseases, however, tuberculosis is most widespread and demands most attention. The common form of this disease is consumption, but the bacteria may attack other 254 BACTERIA, YEASTS, AND MOLDS parts of the body, producing other diseases, such as scvofula, hip disease, etc. Consumption must be guarded against by destroying the sputum of patients and avoiding their breath while coughing; and in any form of the disease that produces open sores, the discharges from such sores must be carefully destroyed. In spite of the long-accepted belief, consumption is not hereditary, but is contagious. Its spread through families is due to the close association of patients with the other members of the family. It is a disease associated with small rooms, poor ventilation, and crowded houses where the healthy members of the family live with consumptive patients and frequently sleep with them. Under such conditions contagion is almost sure, and the disease spreads from person to person just as decay spreads from apple to apple in a barrel. More air, more light, more care of the sputum and other dis- charges, greater attention given to guarding against the coughing of the patient, as for example inducing him to cough into cloths that can be burned, — these are the remedies against the spread of the contagion, and strict attention to these facts would soon convince any one that the disease is not hereditary but due to infectious matter disseminated from the patient. The child of a consump- tive mother may even nurse at his mother’s breast with little danger of contagion; but sleeping with her and breathing her breath while she is coughing is very likely to give him the disease and lead to the erroneous belief that he inherited it from his mother. GENERAL SANITARY RULES 255 GENERAL RULES There are a few simple rules whose observance will reduce the chances of contagion. These rules should be followed by all, but it is particularly important that chil- dren in every household, and especially children in schools, should be taught their significance. The most important rules are: Do not spit on the floor. Do not put the fingers in the mouth. Do not wet the fingers in the mouth for the purpose of turning the leaves of books, especially library books, inasmuch as book leaves are sometimes the lurking places of disease bacteria. Do not put pencils in the mouth. Do not put money in the mouth. This is extremely important, because money is liable to come in contact with all sorts of people and to become contaminated with many kinds of disease bacteria. Do not put into the mouth anything that another per- son has had in his mouth. This refers to gum, apple cores, candy, whistles, bean blowers, drinking cups, etc. Turn the face aside from others when coughing. This will sometimes prevent contagion passing from one per- son to another, inasmuch as the breath in coughing distributes disease germs. Be always particular about personal cleanliness, fre- quently washing the face and hands. CHAPTER XVII DISINFECTION In every household the problem of disinfection is sure to arise in connection with contagious diseases, and it is a question of more or less serious import according to the seriousness of the disease and the number of inmates in the house. The purpose of all disinfection is to prevent the spread of contagious diseases from one person to another. Hence it is desired to destroy the microédrgan- isms which cause the disease. If this can be done there will be no chance of contagion, but until it is done there is always a possibility that a healthy person may contract disease by coming in contact with the germs. In connection with the treatment of infected material two terms are frequently confused. An antiseptic is a material or a treatment which checks the growth of bac- teria, though it does not necessarily kill them all. It may prevent their development without destroying their life. The term germicide, when properly used, refers to treatment which totally destroys all microérganisms. The agents which are used as antiseptics are also commonly capable of acting as germicides if they are used in larger quantities, and, on the other hand, germi- cidal substances may be only antiseptic if used in small quantities. In considering the question of disinfection in the household there are always two important questions to 2 256 PHYSICAL DISINFECTING AGENTS 257 be considered: (1) What disinfectants are capable of destroying the bacteria? (2) How can these agents be most practically applied? It is of course manifest that not all germicides can be used under all conditions. Vio- lent poisons, like corrosive sublimate, might be used in some cases, while it would be out of the question to use them in others. The question, therefore, of the appli- cation of the disinfectants is of even more importance than a knowledge of these antiseptics themselves. DISINFECTING AGENTS — PHYSICAL The physical agencies which destroy microdrganisms have already been considered in previous chapters, and a summary only is here needed. They are briefly the following : Heat.