The Story Of Germ Life.
by H. W. Conn.
PREFACE.
Since the first edition of this book was published the popular idea of bacteria to which attention was drawn in the original preface has undergone considerable modification. Experimental medicine has added constantly to the list of diseases caused by bacterial organisms, and the general public has been educated to an adequate conception of the importance of the germ as the chief agency in the transmission of disease, with corresponding advantage to the efficiency of personal and public hygiene. At the same time knowledge of the benign bacteria and the enormous role they play in the industries and the arts has become much more widely diffused. Bacteriology is being studied in colleges as one of the cultural sciences; it is being widely adopted as a subject of instruction in high schools; and schools of agriculture and household science turn out each year thousands of graduates familiar with the functions of bacteria in daily life. Through these agencies the popular misconception of the nature of micro- organisms and their relations to man is being gradually displaced by a general appreciation of their manifold services. It is not unreasonable to hope that the many thousands of copies of this little manual which have been circulated and read have contributed materially to that end. If its popularity is a safe criterion, the book has amply fulfilled its purpose of placing before the general reader in a simple and direct style the main facts of bacteriology. Beginning with a discussion of the nature of bacteria, it shows their position in the scale of plant and animal life. The middle chapters describe the functions of bacteria in the arts, in the dairy, and in agriculture. The final chapters discuss the relation of bacteria to disease and the methods by which the new and growing science of preventive medicine combats and counteracts their dangerous powers.
JULY, 1915.
THE STORY OF GERM LIFE.
CHAPTER I.
BACTERIA AS PLANTS.
During the last fifteen years the subject of bacteriology [Footnote: The term microbe is simply a word which has been coined to include all of the microscopic plants commonly included under the terms bacteria and yeasts.] has developed with a marvellous rapidity. At the beginning of the ninth decade of the century bacteria were scarcely heard of outside of scientific circles, and very little was known about them even among scientists. Today they are almost household words, and everyone who reads is beginning to recognise that they have important relations to his everyday life.
The organisms called bacteria comprise simply a small cla.s.s of low plants, but this small group has proved to be of such vast importance in its relation to the world in general that its study has little by little crystallized into a science by itself. It is a somewhat anomalous fact that a special branch of science, interesting such a large number of people, should be developed around a small group of low plants. The importance of bacteriology is not due to any importance bacteria have as plants or as members of the vegetable kingdom, but solely to their powers of producing profound changes in Nature. There is no one family of plants that begins to compare with them in importance. It is the object of this work to point out briefly how much both of good and ill we owe to the life and growth of these microscopic organisms. As we have learned more and more of them during the last fifty years, it has become more and more evident that this one little cla.s.s of microscopic plants fills a place in Nature"s processes which in some respects balances that filled by the whole of the green plants. Minute as they are, their importance can hardly be overrated, for upon their activities is founded the continued life of the animal and vegetable kingdom. For good and for ill they are agents of neverceasing and almost unlimited powers.
HISTORICAL.
The study of bacteria practically began with the use of the microscope. It was toward the close of the seventeenth century that the Dutch microscopist, Leeuwenhoek, working with his simple lenses, first saw the organisms which we now know under this name, with sufficient clearness to describe them. Beyond mentioning their existence, however, his observations told little or nothing.
Nor can much more be said of the studies which followed during the next one hundred and fifty years. During this long period many a microscope was turned to the observation of these minute organisms, but the majority of observers were contented with simply seeing them, marvelling at their minuteness, and uttering many exclamations of astonishment at the wonders of Nature. A few men of more strictly scientific natures paid some attention to these little organisms. Among them we should perhaps mention Von Gleichen, Muller, Spallanzani, and Needham. Each of these, as well as others, made some contributions to our knowledge of microscopical life, and among other organisms studied those which we now call bacteria. Speculations were even made at these early dates of the possible causal connection of these organisms with diseases, and for a little the medical profession was interested in the suggestion. It was impossible then, however, to obtain any evidence for the truth of this speculation, and it was abandoned as unfounded, and even forgotten completely, until revived again about the middle of the 19th century. During this century of wonder a sufficiency of exactness was, however, introduced into the study of microscopic organisms to call for the use of names, and we find Muller using the names of Monas, Proteus, Vibrio, Bacillus, and Spirillum, names which still continue in use, although commonly with a different significance from that given them by Muller. Muller did indeed make a study sufficient to recognise the several distinct types, and attempted to cla.s.ssify these bodies. They were not regarded as of much importance, but simply as the most minute organisms known.
Nothing of importance came from this work, however, partly because of the inadequacy of the microscopes of the day, and partly because of a failure to understand the real problems at issue.
When we remember the minuteness of the bacteria, the impossibility of studying any one of them for more than a few moments at a time --only so long, in fact, as it can be followed under a microscope; when we remember, too, the imperfection of the compound microscopes which made high powers practical impossibilities; and, above all, when we appreciate the looseness of the ideas which pervaded all scientists as to the necessity of accurate observation in distinction from inference, it is not strange that the last century gave us no knowledge of bacteria beyond the mere fact of the existence of some extremely minute organisms in different decaying materials. Nor did the 19th century add much to this until toward its middle. It is true that the microscope was vastly improved early in the century, and since this improvement served as a decided stimulus to the study of microscopic life, among other organisms studied, bacteria received some attention.
Ehrenberg, Dujardin, Fuchs, Perty, and others left the impress of their work upon bacteriology even before the middle of the century. It is true that Schwann shrewdly drew conclusions as to the relation of microscopic organisms to various processes of fermentation and decay--conclusions which, although not accepted at the time, have subsequently proved to be correct. It is true that Fuchs made a careful study of the infection of "blue milk,"
reaching the correct conclusion that the infection was caused by a microscopic organism which he discovered and carefully studied. It is true that Henle made a general theory as to the relation of such organisms to diseases, and pointed out the logically necessary steps in a demonstration of the causal connection between any organism and a disease. It is true also that a general theory of the production of ail kinds of fermentation by living organisms had been advanced. But all these suggestions made little impression. On the one hand, bacteria were not recognised as a cla.s.s of organisms by themselves--were not, indeed, distinguished from yeasts or other minute animalcuise. Their variety was not mistrusted and their significance not conceived. As microscopic organisms, there were no reasons for considering them of any more importance than any other small animals or plants, and their extreme minuteness and simplicity made them of little interest to the microscopist. On the other hand, their causal connection with fermentative and putrefactive processes was entirely obscured by the overshadowing weight of the chemist Liebig, who believed that fermentations and putrefactions were simply chemical processes.
Liebig insisted that all alb.u.minoid bodies were in a state of chemically unstable equilibrium, and if left to themselves would fall to pieces without any need of the action of microscopic organisms. The force of Liebig"s authority and the brilliancy of his expositions led to the wide acceptance of his views and the temporary obscurity of the relation of microscopic organisms to fermentative and putrefactive processes. The objections to Liebig"s views were hardly noticed, and the force of the experiments of Schwann was silently ignored. Until the sixth decade of the century, therefore, these organisms, which have since become the basis of a new branch of science, had hardly emerged from obscurity. A few microscopists recognised their existence, just as they did any other group of small animals or plants, but even yet they failed to look upon them as forming a distinct group. A growing number of observations was acc.u.mulating, pointing toward a probable causal connection between fermentative and putrefactive processes and the growth of microscopic organisms; but these observations were known only to a few, and were ignored by the majority of scientists.
It was Louis Pasteur who brought bacteria to the front, and it was by his labours that these organisms were rescued from the obscurity of scientific publications and made objects of general and crowning interest. It was Pasteur who first successfully combated the chemical theory of fermentation by showing that alb.u.minous matter had no inherent tendency to decomposition. It was Pasteur who first clearly demonstrated that these little bodies, like all larger animals and plants, come into existence only by ordinary methods of reproduction, and not by any spontaneous generation, as had been earlier claimed. It was Pasteur who first proved that such a common phenomenon as. the souring of milk was produced by microscopic organisms growing in the milk. It was Pasteur who first succeeded in demonstrating that certain species of microscopic organisms are the cause of certain diseases, and in suggesting successful methods of avoiding them.
All these discoveries were made in rapid succession. Within ten years of the time that his name began to be heard in this connection by scientists, the subject had advanced so rapidly that it had become evident that here was a new subject of importance to the scientific world, if not to the public at large. The other important discoveries which Pasteur made it is not our purpose to mention here. His claim to be considered the founder of bacteriology will be recognised from what has already been mentioned. It was not that he first discovered the organisms, or first studied them; it was not that he first suggested their causal connection with fermentation and disease, but it was because he for the first time placed the subject upon a firm foundation by proving with rigid experiment some of the suggestions made by others, and in this way turned the attention of science to the study of micro-organisms.
After the importance of the subject had been demonstrated by Pasteur, others turned their attention in the same direction, either for the purpose of verification or refutation of Pasteur"s views. The advance was not very rapid, however, since bacteriological experimentation proved to be a subject of extraordinary difficulty. Bacteria were not even yet recognised as a group of organisms distinct enough to be grouped by themselves, but were even by Pasteur at first confounded with yeasts. As a distinct group of organisms they were first distinguished by Hoffman in 1869, since which date the term bacteria, as applying to this special group of organisms, has been coming more and more into use. So difficult were the investigations, that for years there were hardly any investigators besides Pasteur who could successfully handle the subject and reach conclusions which could stand the test of time. For the next thirty years, although investigators and investigations continued to increase, we can find little besides dispute and confusion along this line. The difficulty of obtaining for experiment any one kind of bacteria by itself, unmixed with others (pure cultures), rendered advance almost impossible. So conflicting were the results that the whole subject soon came into almost hopeless confusion, and very few steps were taken upon any sure basis. So difficult were the methods, so contradictory and confusing the results, because of impure cultures, that a student of to-day who wishes to look up the previous discoveries in almost any line of bacteriology need hardly go back of 1880, since he can almost rest a.s.sured that anything done earlier than that was more likely to be erroneous than correct.
The last fifteen years have, however, seen a wonderful change. The difficulties had been mostly those of methods of work, and with the ninth decade of the century these methods were simplified by Robert Koch. This simplification of method for the first time placed this line of investigation within the reach of scientists who did not have the genius of Pasteur. It was now possible to get pure cultures easily, and to obtain with such pure cultures results which were uniform and simple. It was now possible to take steps which had the stamp of accuracy upon them, and which further experiment did not disprove. From the time when these methods were thus made manageable the study of bacteria increased with a rapidity which has been fairly startling, and the information which has acc.u.mulated is almost formidable. The very rapidity with which the investigations have progressed has brought considerable confusion, from the fact that the new discoveries have not had time to be properly a.s.similated into knowledge. Today many facts are known whose significance is still uncertain, and a clear logical discussion of the facts of modern bacteriology is not possible. But sufficient knowledge has been acc.u.mulated and digested to show us at least the direction along which bacteriological advance is tending, and it is to the pointing out of these directions that the following pages will be devoted.
WHAT ARE BACTERIA?
The most interesting facts connected with the subject of bacteriology concern the powers and influence in Nature possessed by the bacteria. The morphological side of the subject is interesting enough to the scientist, but to him alone. Still, it is impossible to attempt to study the powers of bacteria without knowing something of the organisms themselves. To understand how they come to play an important part in Nature"s processes, we must know first how they look and where they are found. A short consideration of certain morphological facts will therefore be necessary at the start.
FORM OF BACTERIA.
In shape bacteria are the simplest conceivable structures.
Although there are hundreds of different species, they have only three general forms, which have been aptly compared to billiard b.a.l.l.s, lead pencils, and corkscrews. Spheres, rods, and spirals represent all shapes. The spheres may be large or small, and may group themselves in various ways; the rods may be long or short, thick or slender; the spirals may be loosely or tightly coiled, and may have only one or two or may have many coils, and they may be flexible or stiff; but still rods, spheres, and spirals comprise all types.
In size there is some variation, though not very great. All are extremely minute, and never visible to the naked eye. The spheres vary from 0.25 u to 1.5 u (0.000012 to 0.00006 inches). The rods may be no more than 0.3 u in diameter, or may be as wide as 1.5 u to 2.5 u, and in length vary all the way from a length scarcely longer than their diameter to long threads. About the same may be said of the spiral forms. They are decidedly the smallest living organisms which our microscopes have revealed.
In their method of growth we find one of the most characteristic features. They universally have the power of multiplication by simple division or fission. Each individual elongates and then divides in the middle into two similar halves, each of which then repeats the process. This method of multiplication by simple division is the distinguishing mark which separates the bacteria from the yeasts, the latter plants multiplying by a process known as budding. Fig. 2 shows these two methods of multiplication.
While all bacteria thus multiply by division, certain differences in the details produce rather striking differences in the results.
Considering first the spherical forms, we find that some species divide, as described, into two, which separate at once, and each of which in turn divides in the opposite direction, called Micrococcus, (Fig. 3). Other species divide only in one direction.
Frequently they do not separate after dividing, but remain attached. Each, however, again elongates and divides again, but all still remain attached. There are thus formed long chains of spheres like strings of beads, called Streptococci (Fig. 4). Other species divide first in one direction, then at right angles to the first division, and a third division follows at right angles to the plane of the first two, thus producing solid groups of fours, eights, or sixteens (Fig 5), called Sarcina. Each different species of bacteria is uniform in its method of division, and these differences are therefore indications of differences in species, or, according to our present method of cla.s.sification, the different methods of division represent different genera. All bacteria producing Streptococcus chains form a single genus Streptococcus, and all which divide in three division planes form another genus, Sarcina, etc.
The rod-shaped bacteria also differ somewhat, but to a less extent. They almost always divide in a plane at right angles to their longest dimension. But here again we find some species separating immediately after division, and thus always appearing as short rods (Fig. 6), while others remain attached after division and form long chains. Sometimes they appear to continue to increase in length without showing any signs of division, and in this way long threads are formed (Fig. 7). These threads are, however, potentially at least, long chains of short rods, and under proper conditions they will break up into such short rods, as shown in Fig. 7a. Occasionally a rod species may divide lengthwise, but this is rare. Exactly the same may be said of the spiral forms. Here, too, we find short rods and long chains, or long spiral filaments in which can be seen no division into shorter elements, but which, under certain conditions, break up into short sections.
RAPIDITY OF MULTIPLICATION.
It is this power of multiplication by division that makes bacteria agents of such significance. Their minute size would make them harmless enough if it were not for an extraordinary power of multiplication. This power of growth and division is almost incredible. Some of the species which have been carefully watched under the microscope have been found under favourable conditions to grow so rapidly as to divide every half hour, or even less. The number of offspring that would result in the course of twenty-four hours at this rate is of course easily computed. In one day each bacterium would produce over 16,500,000 descendants, and in two days about 281,500,000,000. It has been further calculated that these 281,500,000,000 would form about a solid pint of bacteria and weigh about a pound. At the end of the third day the total descendants would amount to 47,000,000,000,000, and would weigh about 16,000,000 pounds. Of course these numbers have no significance, for they are never actual or even possible numbers.
Long before the offspring reach even into the millions their rate of multiplication is checked either by lack of food or by the acc.u.mulation of their own excreted products, which are injurious to them. But the figures do have interest since they show faintly what an unlimited power of multiplication these organisms have, and thus show us that in dealing with bacteria we are dealing with forces of almost infinite extent.
This wonderful power of growth is chiefly due to the fact that bacteria feed upon food which is highly organized and already in condition for absorption. Most plants must manufacture their own foods out of simpler substances, like carbonic dioxide (Co2) and water, but bacteria, as a rule, feed upon complex organic material already prepared by the previous life of plants or animals. For this reason they can grow faster than other plants. Not being obliged to make their own foods like most plants, nor to search for it like animals, but living in its midst, their rapidity of growth and multiplication is limited only by their power to seize and a.s.similate this food. As they grow in such ma.s.ses of food, they cause certain chemical changes to take place in it, changes doubtless directly connected with their use of the material as food. Recognising that they do cause chemical changes in food material, and remembering this marvellous power of growth, we are prepared to believe them capable of producing changes wherever they get a foothold and begin to grow. Their power of feeding upon complex organic food and producing chemical changes therein, together with their marvellous power of a.s.similating this material as food, make them agents in Nature of extreme importance.
DIFFERENCES BETWEEN DIFFERENT SPECIES OF BACTERIA.
While bacteria are thus very simple in form, there are a few other slight variations in detail which a.s.sist in distinguishing them.
The rods are sometimes very blunt at the ends, almost as if cut square across, while in other species they are more rounded and occasionally slightly tapering. Sometimes they are surrounded by a thin layer of some gelatinous substance, which forms what is called a capsule (Fig. 10). This capsule may connect them and serve as a cement, to prevent the separate elements of a chain from falling apart.
Sometimes such a gelatinous secretion will unite great ma.s.ses of bacteria into cl.u.s.ters, which may float on the surface of the liquid in which they grow or may sink to the bottom. Such ma.s.ses are called zoogloea, and their general appearance serves as one of the characters for distinguishing different species of bacteria (Fig. 10, a and b). When growing in solid media, such as a nutritious liquid made stiff with gelatine, the different species have different methods of spreading from their central point of origin. A single bacterium in the midst of such a stiffened ma.s.s will feed upon it and produce descendants rapidly; but these descendants, not being able to move through the gelatine, will remain cl.u.s.tered together in a ma.s.s, which the bacteriologist calls a colony. But their method of cl.u.s.tering, due to different methods of growth, is by no means always alike, and these colonies show great differences in general appearance. The differences appear to be constant, however, for the same species of bacteria, and hence the shape and appearance of the colony enable bacteriologists to discern different species (Fig. II). All these points of difference are of practical use to the bacteriologist in distinguishing species.
SPORE FORMATION.
In addition to their power of reproduction by simple division, many species of bacteria have a second method by means of spores.
Spores are special rounded or oval bits of bacteria protoplasm capable of resisting adverse conditions which would destroy the ordinary bacteria. They arise among bacteria in two different methods.
Endogenous spores.--These spores arise inside of the rods or the spiral forms (Fig. 12). They first appear as slight granular ma.s.ses, or as dark points which become gradually distinct from the rest of the rod. Eventually there is thus formed inside the rod a clear, highly refractive, spherical or oval spore, which may even be of a greater diameter than the rod producing it, thus causing it to swell out and become spindle formed [Fig. 12 c]. These spores may form in the middle or at the ends of the rods (Fig.
12). They may use up all the protoplasm of the rod in their formation, or they may use only a small part of it, the rod which forms them continuing its activities in spite of the formation of the spores within it. They are always clear and highly refractive from containing little water, and they do not so readily absorb staining material as the ordinary rods. They appear to be covered with a layer of some substance which resists the stain, and which also enables them to resist various external agencies. This protective covering, together with their small amount of water, enables them to resist almost any amount of drying, a high degree of heat, and many other adverse conditions. Commonly the spores break out of the rod, and the rod producing them dies, although sometimes the rod may continue its activity even after the spores have been produced.
Arthrogenous spores (?).--Certain species of bacteria do not produce spores as just described, but may give rise to bodies that are sometimes called arthrospores. These bodies are formed as short segments of rods. A long rod may sometimes break up into several short rounded elements, which are clear and appear to have a somewhat increased power of resisting adverse conditions. The same may happen among the spherical forms, which only in rare instances form endogenous spores. Among the spheres which form a chain of streptococci some may occasionally be slightly different from the rest. They are a little larger, and have been thought to have an increased resisting power like that of true spores (Fig.
13 b). It is quite doubtful, however, whether it is proper to regard these bodies as spores. There is no good evidence that they have any special resisting power to heat like endogenous spores, and bacteriologists in general are inclined to regard them simply as resting cells. The term arthrospores has been given to them to indicate that they are formed as joints or segments, and this term may be a convenient one to retain although the bodies in question are not true spores.
Still a different method of spore formation occurs in a few peculiar bacteria. In this case (Fig. 14) the protoplasm in the large thread breaks into many minute spherical bodies, which finally find exit. The spores thus formed may not be all alike, differences in size being noticed. This method of spore formation occurs only in a few special forms of bacteria.
The matter of spore formation serves as one of the points for distinguishing species. Some species do not form spores, at least under any of the conditions in which they have been studied.
Others form them readily in almost any condition, and others again only under special conditions which are adverse to their life. The method of spore formation is always uniform for any single species. Whatever be the method of the formation of the spore, its purpose in the life of the bacterium is always the same. It serves as a means of keeping the species alive under conditions of adversity. Its power of resisting heat or drying enables it to live where the ordinary active forms would be speedily killed.
Some of these spores are capable of resisting a heat of 180 degrees C. (360 degrees F.) for a short time, and boiling water they can resist for a long time. Such spores when subsequently placed under favourable conditions will germinate and start bacterial activity anew.
MOTION.
Some species of bacteria have the power of active motion, and may be seen darting rapidly to and fro in the liquid in which they are growing. This motion is produced by flagella which protrude from the body. These flagella (Fig. 15) arise from a membrane surrounding the bacterium, but have an intimate connection with the protoplasmic content. Their distribution is different in different species of bacteria. Some species have a single flagellum at one end (Fig. 15 a). Others have one at each end (Fig. 15 b). Others, again, have, at least just before dividing, a bunch at one or both ends (Fig. 15 c and d), while others, again, have many flagella distributed all over the body in dense profusion (Fig. 15 e). These flagella keep up a lashing to and fro in the liquid, and the lashing serves to propel the bacteria through the liquid.
INTERNAL STRUCTURE.