ESSAYS ON BACTERIOLOGY. 149 



now muicli to say. The subject is of the greatest 

 moment, but is out of place here, since this is a study 

 of pathology, not of practice. 



I shall assume two propositions to be true. First, 

 that the infectious diseases, have, as their prime and 

 essential cause, living poisons, commonly called germs, 

 bacteria, microbes, and that without them these dis- 

 eases do not exist. Second, that many agencies other 

 than the mere presence and growth of bacteria influ- 

 ence the development of the infectious diseases, even 

 to the extent of assuming the role at times of control- 

 ling factors. Can these two propositions be harmon- 

 ized? It is the chief piirpose of this address to show 

 that they can, by showing that the non-bacterial fac- 

 tors influence the development of the infectious dis- 

 eases because they influence the growth of bacteria in 

 the body. And so the whole matter comes down to a 

 proposition which may be expressed in the simple 

 analogy from agriculture, thus: Crops of grain are 

 the products primarily and essentially of certain seeds ; 

 all other factors influence the production of. grain 

 crops by contribution to the growth of those seeds. 

 So infectious diseases are primarily and essentially the 

 products of the growth of disease seeds or germs; all 

 other factors influence their development by contri- 

 ibution to the growth of these germs in the body. But, 

 ^ let me repeat, and be it remembered, this is the state- 

 ment for pathological, not necessarily for clinical 



