Lesions 551 



It seems, therefore, as if there was a radical difference be- 

 tween the natural and experimental hog cholera, and much 

 doubt is thrown upon the specificity of the micro-organism. 

 In the recent work of de Schweinitz and Dorset,* Nilesf 

 and Dorset, Bolton and McBryde,J it has been shown that 

 there is a form of hog-cholera that can be transmitted by 

 subcutaneous injection of the filtered and bacteria-free blood- 

 serum of hogs ill of the disease, and that immunity could be 

 conferred upon hogs by treatment with the desiccated blood 

 and serum of such animals. This seems to make it certain 

 that hog cholera is caused by some unseen and unknown 

 virus and that the bacillus of Salmon and Smith is an in- 

 cidental and probably accidental factor, not responsible for 

 the disease itself, but only for certain of its clinical pecu- 

 liarities. The form of hog-cholera resulting from successful 

 inoculation with the bacillus is unlike the real disease in 

 not being contagious, but that caused by the filtered blood- 

 serum of sick hogs corresponds perfectly with the sponta- 

 neous disease, and is quite as contagious. The hog-cholera 

 bacillus is markedly pathogenic for laboratory animals. Small 

 quantities introduced subcutaneously into rabbits or mice 

 kill them in from seven to twelve days. Guinea-pigs are 

 less susceptible, o.i c.c. of a virulent culture often being 

 required to kill them. The animal appears quite well for 

 three or four days, then begins to sit quietly in the cage 

 and eat but little, or refuses to eat at all, until death takes 

 place. 



Pigeons are still more refractory, and Smith found that 

 0.75 c.c. of a bouillon culture injected into the breast- 

 muscles was required to kill them. 



In Smith's experiments one four-millionth of a cubic 

 centimeter of a bouillon culture injected subcutaneously 

 into a rabbit was sufficient to cause its death. The tem- 

 perature abruptly rises 2-3 C., and remains high until 

 death. Subcutaneous injection of larger quantities may 

 kill in five days. Injected intravenously in small doses the 

 bacillus may kill rabbits in forty-eight hours. 



Lesions. When the rabbit is examined post-mortem, 



* Circular No. 41 of the Bureau of Animal Industry of the U. S. 

 Dept. of Agriculture, 1903. 



t Circular No. 43. 



t Bull. No. 72, Bureau of Animal Industry, U. S. Dept. of Agricul- 

 ture, 1905. 



