APPENDIX 391 



the human and bovine types of tubercle bacilli. Quantita- 

 tively, and with respect to the effect of glycerin, however, 

 there is a marked difference in the great majority of cultures, 

 so great in fact that almost without exception the type can 

 be determined from cultures alone. This difference is constant 

 in one factor only, viz., amount and rapidity of growth in 

 early cultures. In classifying our cultures according to this 

 characteristic, we can broadly say that all bovine types of 

 bacilli are dysgonic (sparse growth) and all human types of 

 bacilli are eugonic (moderate or luxuriant growth). The 

 question remains, What is the best medium for eliciting this 

 difference ? Any medium used must fulfil certain conditions. 



1. It must be especially adapted for the growth of the 

 eugonic viruses, so that the best possible growth is obtained. 



2. It would be preferable if the growth of the dysgonic 

 virus were somewhat retarded on the medium. This will 

 widen the gap as far as possible. 



3. The medium must be nearly uniform in its results ; that 

 is, growth should not fluctuate with the different batches of 

 medium used. 



We have found that glycerin egg is by far the best medium 

 for this purpose. . . . Cobbett (Royal Commission) made 

 comparisons of the two types of organisms on both serum and 

 glycerin serum. While the human cultures were far more 

 vigorous with the use of glycerin serum, the bovine cultures 

 were either restrained, or if aided by its presence, the increase 

 in growth was slight. This difference he found in early 

 cultures to be of diagnostic value in the separation of the 

 two types. We also noticed that primary cultures of the 

 bovine type repeatedly failed on glycerin egg, whereas the 

 primary cultures of the human type were usually markedly 

 increased in luxuriance. The reading of Cobbett's results 

 led us to adopt glycerin egg as the basic differential medium. 



Giving then the results in terms of glycerin, the following 

 general conclusions may be drawn. 



(a). All cultures* growing luxuriantly on glycerin egg from 

 the start are of the human type. 



(6). All cultures* growing sparsely, or even not at all, on 



* No direct cultures were attempted. Guinea-pigs were inoculated and 

 killed in three to five weeks, and inoculations made from tuberculous 

 lymph nodes and spleen on to plain egg media (Dorset), glycerin egg 

 media (Lubenau), and glycerin potato. Intravenous inoculation into 

 rabbits was used in confirmation of type of culture. If rabbit survived 

 injection of i mgr. of culture for 60 days, then human type. 



