ESSAYS ON BACTERIOLOGY. 23 



'valuable facts, left them witlioiit satisfactory explana- 

 tion. I have already emphasized the fact that bac- 

 teriology has placed this and kindred investigations 

 upon a more secure foundation; has laid down the 

 lines more sharply, and given to means and methods n 

 more definite aim. How this is true must be evident. 

 A definite material thing having become known as 

 the essential infecting agent, the methods of its identi- 

 fication, its life-history and the conditions of its dura- 

 bility established, we at once know what to search for 

 in the endeavor to trace the poison from place to place 

 or person to person. Thus earth, air, water, foods, 

 hands, instruments, fomites of various kinds, are made 

 to yield their secrets, and are known as, not hypothet- 

 ical, but proven carriers of disease. To draw illustra- 

 tion again from the great scourge: If it be shown 

 that the tubercle bacillus is the sinning agent in the 

 tiiberculous material, that it exists in the products of 

 the lesions, that it retains its vitality through long peri- 

 ods under apparently adverse conditions, that it can 

 be detected in its hiding places outside the body, and, 

 with virulence unchanged, can be traced through 

 milk, clothing, furniture, floors and dust; if these 

 things are true, is it to be wondered at that they have 

 modified the older opinions, and are leading many to 

 believe that we have come nearer to a solution of one 

 •of the medical riddles of the ages? 



Among all the subjects which might be brought 

 under the title of this paper there is, perhaps, nothing 



