BY PROFESSOR CROOKSHANK. 36 



received tubercular spiituin with their food. lo one killed in 

 eight weeks, there were 13 nodules in the small intestine and 

 mesenteric glands. In the second calf killed in 19 weeks, the 

 result was absolutely negative. 



Dr. Ravenel, in the course of a very elaborate inquiry, 

 made some experiments of an equally positive character. 

 Four calves, were, as in my original experiment, inoculated 

 intra-peritoneally with tubercular sputum. In one case the 

 result was negative. The other three were all infected, the 

 lesions in two being extensive. On the other hand the re- 

 sults were uniformly negative when Dr. Ravenel mixed human 

 tubercular sputum with the food. To sum up, the evidence is 

 conclusive as to the possibility of grafting human tubercle in 

 bovine tissues, but the experiments are not invariably success- 

 ful. The results are, I think, to be explained in this way. 

 Human and bovine tuberculosis are distinct varieties of the 

 same disease. They are variations resulting from cultivation 

 on different soils. Bearing this in mind, we would hardly 

 expect that the attempts to transmit human tubercle to cattle 

 would be always successful. Too much stress cannot be laid 

 upon the necessity of realising the differences which exist in 

 the nature of the soil upon which a virus is inoculated. This 

 is very well illustrated in the inoculation of human small -pox 

 upon cattle. Smallpox is essentially a disease peculiar to man. 

 It has never been known to attack cattle, but the virus of 

 smallpox can, in exceptional cases, be cultivated on bovine 

 tissues. The experiments are so difficult to carry out, that 

 many have failed, and have positively refused to believe in the 

 successful results of others. Variolation of the cow is never- 

 theless a fact, and so marked is the effect of cultivating the 

 smallpox virus upon a soil which is foreign to it, that the 

 highly infectious disease in man becomes transformed in cattle 

 into a mild disease which is not infectious. The effect of a 

 foreign soil is also illustrated in the result of inoculating 

 sheep-pox in man. This highly infectious disease of sheep when 

 grafted on human tissue is also transformed into a mild 

 non-infectious disorder. 



We can take it for granted that in exceptional cases 

 human tubercular virus can be experimentally grafted on 

 cattle, and we have good reason to believe that in exceptional 

 cases, bovine bacilli may invade the human tissues. I refer to 

 those rare cases in which there has been accidental inoculation. 

 Veterinary surgeons, butchers, and others whose occupation 



