30 SPECIFIC AND CONTAGIOUS DISEASES. 



contaminate the whole circulating fluid and much of the secre- 

 tions, and produce material sufficient to infect many hundreds 

 of animals. 



Another remarkable difference between these specific con- 

 tagia or poisons, and other toxic agents, is that many of 

 them, when received into the animal body, possess the pro- 

 perty of exhausting the constitution of its susceptibility, or at 

 least greatly lessening it, to another successful inoculation with 

 the same virus. 



In addition to this analogy between the laws regulating the 

 action of ordinary and specific animal poisons, experimental 

 research has taught us that the modes of their operation are 

 likewise very much the same, in so far as, being absorbed by 

 the veins, they, like ordinary poisonous or medicinal agents, 

 enter the circulation, produce upon the constituents of the 

 blood a peculiar or specific action, pass through the blood, and 

 ultimately produce their specific local results in specific ele- 

 mental tissue changes or otherwise, in certain determinate 

 parts or tissues, between which and these specific implanted 

 agents there is a particular affinity. 



Nature of the Contagium of Contagious Diseases. — The 

 disease-producing agent or material developed and elaborated 

 in the animal body, which, when implanted into another 

 animal organism, induces a similar disease, is known by the name 

 of contagiuTii, specific virus, or mater ies morhi. It has been 

 variously regarded as consisting of noxious gases, palludial or 

 animal effluvia, organic molecules, or germs which have been 

 in existence with, and are now detached from, living animal 

 matter. Certainly the direction in which present pathological 

 experimental research seems to point is that of regarding all 

 contagious and specific diseases as the result of the introduc- 

 tion into the animal body of distinct particulate and living- 

 organisms — true animate contagia — which have not been the 

 result of, or developed or elaborated from, degraded or degene- 

 rating proto or bioplasm, but are the descendants of similarl}^ 

 endowed and organized forms, living entities, proceeding from, 

 and tending to, the generation or development of similar 

 living entities. 



This latest view of the origin of infectious and specific 

 diseases, as consisting in individual livino- orsfanisms, although 



