SPECIFIC AND CONTAGIOUS DISEASES. 29 



intrinsically, have an influence in determining the extent or 

 virulence, so to speak, of the specific infecting virus. It is 

 also highly probable that no specific or contagious disease ever 

 originates de novo. This was not always the opinion, nor even 

 now are all agreed upon the certainty of it. 



Whether contagious diseases are in every instance of their 

 appearance to be regarded as originating from the reception 

 and development in those affected of the germs of the parti- 

 cular malady — it matters not whether this fructifying element 

 be specific organisms, living and particulate, which by virtue of 

 their inherent life-energy originate this particular diseased 

 action, or are merely the bearers of the more inappreciable and 

 occult agent, the specific contagium — it is at least certain that 

 these disease-producing germs, when received, whether animate 

 oontagia or not, comport themselves in the production of the 

 morbid conditions and phenomena which follow their recep- 

 tion into the animal body in a manner analogous to ordinary 

 poisons, or medicinal agents given in poisonous doses, and that 

 they are regulated by general laws applicable to both classes of 

 agents. 



But although specific disease-germs, or poisons, are, like 

 ordinary poisonous agents, possessed of certain common 

 properties, and yield obedience to several laws of general 

 applicability, there are still many points of divergence or 

 pecuharity in the actions of animal poisons inducing con- 

 tagious or specific disease, which peculiarities account for much 

 that is specific in the natural history of these maladies. 



They resemble ordinary poisons in that when received mto 

 an animal body they are followed by the exhibition of certain 

 phenomena or specific actions; they also, like poisons, pre- 

 serve between their entrance and development of symptoms a 

 varying period of repose ; and further, the phenomena result- 

 ing from the reception of both may vary in accordance with 

 the quantity received, and the power or capacity of the re- 

 cipient. 



Morbid poisons differ from ordinary poisonous agents most 

 markedly in that when received into the animal body there 

 is conferred upon them the power of indefinite increase or 

 multiplication. The most minute quantity of the virus of 

 glanders will, when introduced into the system of the horse, 



