Nc. 6. DEPARTMENT OF AGRICULTURE. 471 



onlj occurs after four or five days, sometimes logger; but by passing 

 this microbe from rabbit to rabbit, it rai)idly acquires such a degree 

 of virulence that it kills rabbits in a few hours. But this bacillus, 

 although become so virulent for rabbits, has lost all its virulence 

 for swine, from which it comes originally; we can inoculate swine 

 with large doses without killing them, and even without making 

 them sick. 



What I have said of the bacillus of "rouget du pore" applies also, 

 and nearly as exactly, to the trypanosoma of douriue in the horse. 



This parasite of a higher order is inoculable into dogs, the white 

 mouse, a«id the white rat, among other animals. After some pas- 

 sages from mouse to mouse or from rat to rat, it acquires such a 

 degree of virulence that the animals die in a few days showing an 

 enormous number of trypanosomes in the blood. When, however, 

 we inoculate the rat or mouse with this same trypanosoma after a 

 certain number of passages through dogs, it no longer succeeds in 

 killing them nor does it make them sick. The prolonged adaptation 

 of the trypaoosoma to the organism of the dog causes it to lose its 

 power of developing in the organism of the white mouse or white rat; 

 but a most curious thing, the trypanosoma of the dog remains always 

 just as virulent for the horse. 



Finallv, I have shown that the tubercle bacillus from man or from 

 cows cultivated in the peritoneal cavity of the chicken protected from 

 phagocytic action, thanks to the protection of a collodion sac, ac- 

 quires little by little the characters of the avian tubercle bacillus and 

 becomes incapable of killing guinea-pigs, or kills them with lesions 

 analogous to those of avian tuberculosis. 



All these lead me to thiuk that the results obtained by Prof. 

 Koch proceed from causes of the same ki«d. Cattle rarely take 

 tuberculosis from man, but when for some reason or other the re- 

 sistance of the cells is modified, diminished or suppressed, the human 

 bacillus can multiply and invade the organs of the subject in which 

 the resistance has been overcome. After this, the bacillus adapted 

 to its new surroundings is able to develop in other healthy cattle, 

 which would show themselves refractory to the action of this same 

 bacillus if it came directly from man. Let us admit for an instant 

 that if cattle are really refractory to human tuberculosis, has one the 

 right to conclude from this that the reverse is equally true? No, a 

 hundred times no; this would be contrary to all the principles of the 

 experimental method. It would be above all, contrary to facts. 

 If experimental facts are lacking, and for cause, all clinical facts 

 abound which prove the possibility of the transmissibility to man 

 of tuberculosis of cattle. IMany have seen veterisiarians who have 

 wounded themselves while making autopsies on tubercular cows. 

 Some have gotten well, thanks to prompt and radical surgical inter- 

 vention, such as our colleague Jensen, of the Veterinary School of 



