390 



BOVINE AND HUMAN TYPES OF 

 TUBERCLE BACILLI.* 



i. SMITH REACTION. 



Theobald Smith, in 1896, first drew attention to the 

 existence of two types oi tubercle bacilli in mammals, and in 

 1898 he published a systematic comparative study of bacilli 

 isolated from man and cattle, and pointed out the differences 

 between the two types as summarised on page 277. Pursuing 

 the research further, he found that when grown in slightly 

 acid glycerin broth, the two types give different reaction 

 curves. 



Glycerin Broth. The human type caused at first a lessening 

 of the acidity of the medium until it became nearly but not 

 quite neutral ; thereafter the acidity increased until it again 

 approached or slightly exceeded the original reaction. 



The bovine type in the early stages of its growth rendered 

 the medium less acid, neutral, or even alkaline ; and then it 

 may so remain or become acid again, but never up to the 

 original degree. 



The British Royal Commission for this test also used 

 glycerin litmus milk (milk freed from cream, plus 5 per cent 

 of glycerin, plus 5 per cent of 5 per cent watery solution of 

 Merck's purified litmus). They found that all human viruses 

 which grew vigorously on this medium at first caused an 

 increase of alkalinity, and later acidity and clotting ; if the 

 growth was less vigorous, acidity resulted without clotting. 

 The bovine viruses which grew vigorously in the medium 

 caused acidity finally, but never clotted the milk ; the poorly 

 growing viruses left the milk alkaline. They concluded that 

 the reaction curves can be so grouped as to form a scale of 

 the final reactions with complete gradations from one type 

 to the other. 



2. CULTURAL CHARACTERS (p. 15). 



The results of our work have led to the conclusion that 

 there is no constant qualitative cultural difference between 



* Abstracted from Vol. V. of " Collected Studies from the Research 

 Laboratory, Department of Health, City of New York, 1910," by Park and 

 Krumwiede, and others. 



