THE PRACTICAL VALUE OF BACTERIOLOGICAL EXAMINATIONS.
NOT much over a decade ago the only means of judging of the sanitary position of a water was by the results of a chemical examination. Yet, notwithstanding the enormous labor and ingenuity bestowed on the work of these chemical methods, and notwithstanding the wonderful accuracy of their results, they could only tell us, when taken by themselves, that a water might or might not be safe in its use as a potable water. A definite, precise, and certain answer could not be given; only an inference more or less likely to be true could be drawn. When it was firmly established that certain diseases were due to certain bacteria, is was thought that we should have in the bacteriological examination a sure, quick,and inexpensive way (and all of these points are necessary in practical work) for determining the fitness of water for drinking purposes. This desideratum has, unfortunately, here too escaped us; but it may not be amiss to fix briefly what is the value of a bacterial examination which can Be carried out rapidly and economically.
The germs of two diseases—typhoid fever and cholera—are so generally recognized as being waterborne that frequently they are looked upon as being the only ones—and with us,in fact, usually typhoid is the only one so carried and the only disease threatening us in impure water; but it is well to remember that other and numerically greater dangers may lurk in polluted waters. While it must be said that the search after typhoid and cholera bacteria directly in drinking water has been successful only in rare and isolated cases, even when water has been known to contain them, still recognition of the danger of large numbers of bacteria in general gives to the bacteriological examination of water a very great value. Polluted waters which would show a high bacterial content may carry and produce infection with pin wo 1 ms or tape worms. The spores of lockjaw and the ant hrax bacilli have also l>een found in such waters. The many miscellaneous bacteria of filthy water may produce blood poisoning when used in the washing of wounds, large or small, us so often happens. It is further recognized that, grave diarrhmns, and that so frequently fatal form, cholera infantum, may also Is* produced by such water, not only by its direct use, but indirectly, when it is used for the washing of vegetables eaten in the raw state or the rinsing of vessels later used for keeping milk. Here the bacteria remaining in the small quantity of water left behind find on the vegetables or in the milk conditions suitable for their growth and development, and are, therefore, introduced in enormous numbers W’hen these substances are eaten later.
As you know, the only thing feasible in many cases is to determine the number of bacteria in a given sample of water, and this can be accomplished in a few days. Even in this simple procedure it must be confessed that the methods are not perfect, as no medium has yet been found which offers equally favorable conditions for thegrowthof all kinds of bacteria. Nor can any provision usually lie made here for those bacteria that will grow only in the absence of air. But fortunately the error introduced here is not a great one, and for comparative results, at which only many of these examinations aim, it can be safely neglected. By such simple means, then, a very close approximation as to the amount of general pollution may be made. It can be shown that purification of a stream hus or has not taken place. Periodic examinations of the water supply will promptly reveal by a rise in the number of bacteria the introduction of an unusual pollution, or the result may give guarantee of the efficiency of the safeguards taken. And we have here the only practical means for testing and controling the working of a filter plant. It being established that a mere numerical determination of bacteria is not in all cases satisfactory, the proposal was made to consider the number of kinds or species of bacteria found, rather than the total number. This proposition is, indeed, a valuable one, for, if a w’ater contains disease-producing bacteria, the pollution that lias brought these will, generally speaking, have also brought a larger variety of other bacteria, and hence the justification of the suggestion. Further, the more numerous the sources of pollution are, the greater will probably be the number of different kinds of bacteria to lie found, as each fresh source will almost certainly introduce one or more new kinds. This means that a water showing many varieties will have been exposed very frequently to the liability of taking up germs capable of causing disease. To carry out this method to its fullest possibilities, the exact nature of each kind ought to be determined; but in most cases this cannot be done on account of the requirements of time and money necessary, but seldom available in such work.
•Paper read at the nineteenth annual convention of the mertcan Water Works ^ association, Columbus, Ohio, ane, 1880-
Instead then of determining all species present, bacteriologists are usually satisfied to determine the presence or absence of fecal bacteria—bacteria always found in the excrement of man and animals— for at present there is no w’ay of saying whether these so-called intestinal or fecal bacteria are from human or from animal excrement. The colon bacillus is the only one usually singled out in this search, since the methods of its discovery are reasonably exact and expeditious; though we are coining to recognize that there are several species, rather than a single one which should come under this head. The viciousness of a find of colon bacilli is apparent when, in this connection, we make the very logical argument that, if the more or less innocuous colon bacillus, indicating human excrement, finds its way constantly into the water under consideration, the typhoid bacillus, which is also carried in the fasces, may at any time invade the water. This reasoning of course, would not hold where these fecal or intestinal bacteria are known to come, not from human, but from animal waste, as for example, by the rain washings of a manured field. In this connection, the consideration of the mere numbers as against the number of kinds, I may quote from Migula, who pointed out that the number of bacteria will depend, not only on the degree or kind of pollution, but also upon a variety of external conditions and temporary variations—sun, light, and so on. lie says:
The number of individuals is merely a result of growth or multiplication influenced by such conditions : the number of different species is a result of the kind and frequency of pollution.
It is sometimes urged that, in practice, water is never free from bacteria, and that even a large number of germs found therein may not render a water unfit for use, since they may all be harmless varieties, and, in further support of this view, the statement is made that many fluids in common use, as milk, ordinarily contain bacteria far in excess of the number found in water True, milk, as it reaches the consumer, even when gathered under the most approved conditions, contains uever less than 5,000 bacteria per cubic centimetre, and may contain 10,000 to 100,000, and even over. But they are few’ in kinds, are mainly air-borne, harmless, nay, often beneficial bacteria, and are found in uch large numbers simply because the milk furnishes for them a good breeding ground. A large number of bacteria in water is to be regarded in quite a different light. Pure water originally contains none, or, at most, few bacteria, and pure water is not, as is milk, a suitable medium for their growth, and, hence, a large number, even irrespective of variety, always indicates a pollution which is certainly suspicious and, in most eases on account of the putrefactive bacteria, positively dangerous.
How many bacteria, then, may a water contain before it must be considered unfit from a sanitary standpoint? Curiously enough, there is no concordance of opinion on this point, and the upper limit is placed by different writers atfrom fifty to 1,000 cubic centimetres—the latterlimit, in my opinion, decidedly too high The true limit in each case must be determined by the judgment of the bacteriologist after analysis of the local conditions—a judgment which will consider the facts given also by the chemist and the engineer.
One drawback encountered by the bacteriologist lies in the fact that water examinations must be made immediately the sample is taken; that is, practically on the spot, and not after a transportation lasting hours or even days. Shipping in ice, more or less heartily recommended by some writers, is never permissible for numerical, and rarely for species determination, for experiments just finished at the university have shown that, in so short a time as four hours after carefully packing in ice. results will be obtained utterly at variance with those of an examination made promptly.
These criticisms so freely made on bacteriological methods are not offered as in any seme derogatory of the methods. On the contrary, it is apparent that we have here means as expeditious, economical, and safe, to say the least, as any others now at our command for the determination of the sanitary quality of w’ater. In fact. Dr. Hurty stated to this convention at Indianapolis that in one of his cases fecal bacteria were discovered in a water several days before the chemical examinations showed any evidence of the new pollution.
For gauging the work of filters and coagulants, we have in bacteriological examination the best or only method—though here I wish to repeat a protest already made against expressing the results of bacteria removed in percents rather than the actual numbers remaining in the water. For to say that ninety-eight per cent, of 1,000,000 originally contained have been removed, means one thing, whereas ninety-eight per cent, of 100 contained means quite another thing—the first case being of apparently equal efficiency with the last, but giving a water still containing 20,000 germs per cubic centimetres; the latter leaving only two per cubic centimetre for the solution of general questions.
To sum up: The bacteriological work must be in conjunction with, and is indispensable to the chemical and the engineering side of sanitary water.