No. 6. DEPARTMENT OF AGRICULTURE. 141 



theii- racial peculiarides by residence in different animals through 

 which the}' are subjected to a difference in food, temperature, and re- 

 sistance. In other words, the struggle for life is carried on io the 

 various species of animals under varying conditions, the result be- 

 ing that in each animal the tubercle bacillus acquires properties 

 which best enable it to carry on life in that particular host. The 

 acquisition of these peculiarities no doubt requires a certain lapse 

 of time, but how much we do not know. We have experimental evi- 

 dence that it does not require a great time to change the tubercle 

 bacillus from a higher into a lower type. By the method of inocula- 

 tion in the peritoneal cavity in collodion sacs Nocard has shown that 

 in from five to eight months both the bovine and human bacillus can 

 be made to acquire the cultural characteristics of the avian bacillus, 

 and to a certain extent its pathogenic action also. A few passages 

 from fowl to fowl during four to six months increased this greatly. 

 By passage through the blind worm Moller has in the course of a 

 year so changed the human tubercle bacillus that it grows like the 

 organism of fish tuberculosis, and has the same temperature reac- 

 tions. It grows best at 20 degrees C, and ceases to grow entirely at 

 30 degrees C. The bacillus of fish tuberculosis, discovered by Du- 

 bard had for its origin the human bacillus, the fish having fed on 

 the sputum and dejecta from a patient far advanced in phthisi. The 

 fish had been subjected to this for about a year before the disease was 

 noticed. 



With these facts before us I do not think we are forcing a point 

 in believing that it is at least possible for the bovine bacillus to 

 become rapidly so changed in the body of man that it will show the 

 cultural and pathogenic peculiarities which we find usually in cul- 

 tures of human origin. For these reasons our observations should 

 be made by preference on cases which are rapid and acute. 



Conclusion. — The evidence at hand forces us to conclude .that 

 human and bovine tuberculosis are but slightly different manifesta- 

 tions of one and the same disease, and that they are intercommu- 

 nicable. Bovine tuberculosis is, therefore, a menace to human 

 health. We are not in a position at present to define positively the 

 extent of this danger, but that it really exists cannot be denied. 

 In the past there has probably been a tendency to exaggeration, but 

 however great this may have been it does now justifj' any attempt 

 at belittling the risk, and it is folly to blind ourselves to it. 



The eradication of bovine tuberculosis is amply justifiable from a 

 purely economical stand-point; viewed in its bearing on human health 

 it becomes a public duty. 



