300 BACTERIOLOGY. 



all facts tend to show that the great majority of cases, 

 in adults at least, come from human infection. The 

 cases where fairly strong proof of bovine infection has 

 been obtained are certainly rare. 



Further, we have the undoubted fact that constant 

 sojourn in one species of animal tends to increase the 

 virulence of the germ for that animal and to lessen it 

 for others. 



Theobald Smith has made the interesting discovery 

 that there is a wide difference between the culture 

 growth of the average bovine bacillus and the average 

 one from human sources, the bovine bacilli being shorter 

 and straighter, and growing less luxuriently than those 

 from man ; and, further, that the bovine bacilli are 

 much more virulent for rabbits. He has found these 

 differences persist for long periods, and believes that 

 the simple passage through a single person in a case of 

 human tnberculosis would not be sufficient to change 

 these characteristics. He has not yet had a chance to 

 examine the bacilli of any case in young children where 

 milk infection was strongly suspected, but in adults 

 not one of some half a dozen cultures showed the 

 bovine characteristics. 



At present it seems fair to assume that bovine bacilli 

 are capable of infecting only those that are very sus- 

 ceptible, such as young children. This question is in 

 great need of further study, and unless proof is 

 brought to show that bovine bacilli never infect human 

 beings, no cattle which are shown to be tubercular 

 should be allowed to furnish milk, or at least none un- 

 sterilized should be used for drinking purposes. The flesh 

 is less harmful, as muscular tissue is seldom infected. 



Bird (Avian) Tuberculosis. Tuberculosis is very com- 



