NOTES ON BACTERIOLOGY.

[Communicated.]

II.

IT most not be forgotten that even in distilled water certain aquatic bacteria multiply. These, however ,cause a rapid disappearance of the pathogenic bacteria. In the cultivation of the latter, which are very delicate and choice in their food, the media of cultivation must be prepared with great care. Unlike the robust saprophytes. which flourish at a lower temperature and are much less choice in their food, to the pathogenic bacteria, if, at least, they are to grow and multiply, must be offered conditions as like as possible to those of the animal body. Hence.it is of no use to make any examination of water shipped to a laboratory for that purpose, since the bacteria sent from a distance do not represent those present when first sent, while the pathogenic bacteria are the most likely of any to have disappeared. The bacterial flora of water also change in a very few hours after having been caught. Some of the forms which are to be found in abundance when the water is first drawn from well, lake, stream, or pipe, will be discovered to have sensibly diminished in numbers, while others, of which there are very few in the beginning, will be found in great, sometimes enormous quantities. If water freshly drawn is examined immediately and then let stand and examined at intervals, it will usually be found that after a very few days only two forms survive, each of which increases very rapidly. One is the mirococcus aquatilis, the other is a fluorescent, non-liquefacient bacillus.

The results of the examination of water not freshly caught will probably be misleading—will almost always be negative. The bacteriological examination, will, therefore, be of no value for the purpose of detecting pathogenic bacteria. For these the cultures must be prepared as soon as ever the water is caught, as it is then that the principal danger is to be looked for from contaminated water. Only under extraordinary conditions—4. e., where there is a source of continuous contamination and when the water is dangerous at all times, is the finding of the organisms, a work of of comparative ease. This was the case when the cholera bacilli were found during the last epidemic of cholera in Hamburg and Altona. To find any pathogenic bacteria under ordinary circumstances and under the most favorable conditions is hard enough; it is especially so, and takes a long time to detect typhoid bacilli in water under any circumstances, owing to the want of definite characteristics in those bacilli themselves. In many cases, more than one examination should be made, since the water from one well may be more or less, or not at all contaminated at different times.

Surface contamination constitutes the principal (probably the only) danger from pollution. As a general rule, if water filters through the soil, it becomes purified. It is held that during a dry season the danger of contamination from the surface is very small—unless, of course, some crack or crevice leads from a privy vault or some similar source of contamination, in which case there is danger of infection. As pathogenic bacteria die out quickly in the soil—within one or two days—it would be difficult for them to pass from their place of deposit Into a well through soil in which there are no crevices. It is not improbable that infection is even more likely to arise from Indirect, than direct sources—that is, from indirect contact of food and vessels for containing food and drink with typhoid excreta rather than from contaminated water. At the same time ” inassen infection,” as the Germans call it, undoubtedly does take place from drinking contaminated water

It will then be seen that the probabilities are that the life of pathogenic bacteria in water is short because under ordinary conditions they cannot find either the conditions for multiplication and growth or for prolonged life. As a result, the danger of the spread of disease by this means soon passes away, unless, indeed, the source of the water supply is subject to continuous contamination from a channel leading to a privy vault —water, as often as not, being infected after it is drawn and carried into the house in infected vessels—as happens also in the case of food. In the case of surface waters too, certain conditions known by experiments of bacteriologists, affect the vitality of pathogenic germs—yet, on account of dilution or because they happen to be absent from the sample of water at the time of its examination, it is often (more often than the other way) impossible to find them. The action of the soil is also a very important factor with respect to the vitality of the bacteria.

A paper read some years ago in London discussed the subject with relation to the cholera spirillum and typhoid bacillus. The experiments were made in sterilized soils of white sand, yellow and garden earth, and peat, under various conditions of moisture. It was thus found that, in the case of the cholera germ in dry soil, it did not live more than two or three days; in ordinary dry soil, about three days; in moist, white sand, seven days.in moist, yellow sand and garden earth, thirty-three days, and, under certain conditions of moisture and evaporation, the germs were alive at the end of 174 days—the life-supporting power of white sand being least. In peat, death al* ways occurred in about twenty-four hours, notwithstanding the amount of moisture. In the case of the typhoid bacillus, in ordinary dry soil the bacilli were found up to the ninth day in the w! itesand; to the eighteenth in yellow, and to the fourteenth in garden earth. In moist, white sand, the germs were alive on the twenty-third day, and in yeilow sand and garden earth on the forty-second day. Peat in the case of the germ caused death in twenty-four hours.

(To be continued.)