We can not, indeed, answer, with the results of experiment and microscopical investigation, questions respecting the infectious diseases with the specific germs of which we are not acquainted, but we may be guided in the matter by other facts. Naegelli says: "Contagion fungi can keep up their peculiar activity in water only for a short time. The purer it is the less food they find in it; they are very soon removed by exhaustion in clear spring-water; and, even in water that contains food for them and where they can multiply fast, degeneration quickly sets in, and they are changed into common ferments."
Inasmuch as we are not acquainted with the germs of typhus and cholera except through their infectious operation, we can not, so long as we use at the same time the air and the water of the infected place, decide whether the epidemic germ is imparted to us by the water or by the air. If only one of the elements could be used while the other could be entirely excluded, we might anticipate a time when investigation should bring us to a decision on the subject. Many cases are now known where cholera and typhus have run their course without any part of the local water having been used as drinking-water, but not a single case where the local air was excluded while the local water was used. A severe epidemic of typhus that prevailed in the city of Basle last fall and winter enforced the lesson that not even the purest water, brought from far away in the Jura, could afford protection against those diseases. With this fact the probability, in cases where the epidemic influence can be ascribed to both the air and the water, that it exists in the water, falls to a minimum. We may then ask, Why might not the infection in these cases have been brought out from the soil by the air? It is not my intention to argue here, where discussion is not possible, against the drinking-water theory; I only call attention to the fact that the most convincing proof of it is wanting. My disbelief in it, however, does not prevent my desiring pure and abundant water for all dwelling-places of man, for we need it, not only as a means of protection against typhus and cholera, but for the daily use of sick and well; not only for the sake of cleanliness and for food, but also as a luxury.
The examination of the fungoids has brought out many facts of great hygienic importance, among them some that concern organic life in the soil. I acknowledge the fact gratefully, but can not abstain from indicating a few points which show the necessity of being guarded in practical hygiene against too hasty conclusions. Mycology would assume more than belongs to it, if it should imagine that hygiene was first placed on a scientific foundation or that it first reached a scientific standing when the cultivation of bacteria was begun, or that it had nothing more to do in the future than to look into the microscope and work with the steaming-pot and wadding-stopper. The professional hygienist has still much else to do; but if he keeps himself familiar with the results of the investigation of the germs, then