RELATIONS TO OTHER SCIENCES 57 



taught, the lesson, even yet not properly taken to heart, that drink- 

 ing-water may be the ready vehicle of a terrible epidemic of cholera. 

 About 1860, striking epidemics of trichinosis first came into public 

 notice, and here, also, belongs the magnificent work of Pasteur, 

 while in 1868, Lister, following in the footsteps of Pasteur, revealed 

 to the world the basis of true cleanliness in asepsis, and in 1876, 

 bacteriology became firmly established as a science by Koch's 

 studies on anthrax. The decade from 1880 to 1890 may be called 

 the golden age of etiology, for in these years were discovered 

 the hitherto unknown parasitic microbes of typhoid fever, tuber- 

 culosis, malaria, Asiatic cholera, diphtheria, and tetanus. The last 

 decade of a century which has well been called " the wonderful," 

 witnessed the discovery of antitoxins by Behring and the beginnings 

 of serum therapy. The list is long, and I have not mentioned 

 nearly all of the discoveries of capital importance, but because of 

 these and their fruits, I am in the habit of saying to my students 

 that with the single exception of the changes effected by the ac- 

 ceptance of the theory of organic evolution, there has been no modi- 

 fication of human opinion within the nineteenth century more 

 wonderful, or more profoundly affecting the general conduct of 

 human life, than that in our attitude toward the nature, the causa- 

 tion, and the prevention of disease that is to say, toward public 

 health science. 



No mere outline like this of the history of public health science 

 can possibly serve to show how, like other applied sciences, this 

 one has not grown as a branch grows from a tree, namely, from 

 a large stem or stock of knowledge, tapering out into thin air, and 

 with its latest growth its least and weakest. That common simile, 

 in which the various divisions of science are represented as branches 

 of the tree of knowledge, is a grotesque survival of a time when 

 neither trees nor science were understood. No simile is perfect 

 or even approximately correct, but one better than the tree and its 

 branches for the origin and relationships of any inductive science 

 is that of a river, rising from various and often obscure sources, 

 growing in size and importance as it proceeds both from the springs 

 within its own bed and by the entrance and contributions of tribu- 

 tary streams, and finally pouring its substance into the mighty 

 ocean of accumulated human knowledge. 



Up to the time of the establishment of the registration of vital 

 statistics in England, in 1839, the stream of public health science, 

 although full of promise, was only a slender thread, but when the 

 results of registration were fully enlisted in its service it visibly 

 widened and deepened. Epidemiology, as has been said, had the 

 honor of giving birth to the science in 1767, and it added to its 

 offspring a rich endowment when, in 1854, Dr. John Snow proved 



