Page:Popular Science Monthly Volume 32.djvu/698

678 repellent in the thought that we are liable to unwittingly consume, in our drinking-water, as we do in much of our uncooked food, such numbers of living things. But this feeling is largely due to the wholly unjustifiable disposition which many persons display to class them among "bugs" and "worms." Nobody thinks of considering the consumption of fresh fruits and vegetables as anything uncanny. And yet all the vegetables and fruits which we commonly use as foods are really made up of vast aggregates of tiny living organisms called cells, each one of which is the analogue of the single organisms called bacteria, and under ordinary conditions one is just as little harmful as the other. The leaves and fruits of some plants are exceedingly poisonous, and yet he who should on that account decline to eat lettuce or peaches would be justly reckoned among Nature's weaklings. The air v/e breathe in inhabited regions always contains considerable numbers of bacteria, but they are for the most part harmless.

We have learned a great deal about these, our invisible friends the bacteria, within the past few years; and as that knowledge has grown, we have found out that lurking among them are a few species, not friends but our most inveterate foes, producing disease and even death. The fact is that, under ordinary favorable sanitary conditions, the bacteria which we are liable to breathe or consume are as harmless as so much air. But if we insist upon drinking dirty water or breathing filthy air, we increase, as we deserve to do, our risk of coming under the influence of the baneful forms.

There are a few diseases common among us, the most important of which are consumption and typhoid fever, which are caused by the presence and action in the body of certain well-defined and well-known species of bacteria. These diseases never occur except under the influence of these particular forms of germs. And the reason why consumption and typhoid fever continually occur is because certain of us get some of these bacteria in the living condition into our bodies, where they grow and induce the disease. All persons are not alike susceptible to the action of these bacteria, naturally or at all times, so that they doubtless not infrequently gain access to our bodies without producing ill effects. Now every intelligent person knows, or ought to know, that water polluted with sewage is not a proper thing to drink; and, while there may be other causes which render it unwholesome, the cause which we know most about is the presence of certain forms of disease-producing bacteria. This knowledge it is which has led to the construction for large towns of expensive systems of water supply, whose reservoirs are situated at considerable distances, where, presumably, no sewage contamination is possible. If we can be certain that the water from our city supplies can not contain sewage or human or animal excretions of any kind, we are pretty safe, so far as our present knowledge goes, in giving ourselves little concern about the number of bacteria which it may contain.