io8 



diminished in quantity ; but it is not increased. No more 

 perfect illustration of this principle can be furnished than 

 an experiment of Rosenberger, which has especial value 

 because this observer would assign to bacteria a subordi- 

 nate role in morbid processes. He found that the boiled 

 blood and tissues of septic animals proven to contain no 

 living bacteria induced septicaemia as certainly as the 

 same blood unboiled. He then placed in one of two 

 flasks containing identical culture-liquids a few drops of 

 the boiled blood, and in the other the same quantity of 

 unboiled blood. Two days later every drop out of the 

 latter flask conveyed septic infection, while large quanti- 

 ties from the former induced no reaction ; every drop of 

 the septic fluid was swarming with bacteria ; in the other 

 flask there were no organisms. 



The virus of an infectious disease must then be some- 

 thing capable of reproduction, and this power is the pe- 

 culiar characteristic of an organism. No unorganized 

 poison, acid, salt, alkaloid, ferment is at present known 

 which is capable of manifesting the phenomena shown 

 by the virus of syphilis, variola, scarlatina, etc. 



Turning to diseases whose parasitic origin is already 

 demonstrated, we find all the characteristics of the in- 

 fectious diseases exquisitely exemplified. Anthrax is 

 marked by a stage of incubation twelve to seventy 

 hours during which the bacilli multiply and effect ac- 

 cess to the blood ; the onset of constitutional disturbance 

 is marked by the presence of numerous bacteria ; with 

 the death and disappearance of these, convalescence be- 

 gins ; the disease is eminently communicable by contact 

 and yet may occur also sporadically and epidemically. 



And this leads me to mention a fact often urged as an 

 objection to the parasite theory : that many infectious 

 diseases are intimately associated with climate, soil, and 

 topographical features, indeed indigenous to certain dis- 

 tricts. This is, in fact, strongly favorable to the germ 

 theory. Many plants and animals of larger growth have 

 decidedly limited habitats ; botanists and zoologists have 

 long since informed us that this same principle applies 



