460 



MILK 



Bovine. 

 Growth more or less moist, not ad- 

 hering to the surface of the me- 

 dium; is diffusible in NaCl solution 

 or broth; initial growth is always 

 sparse; pigment appears only after 

 long cultivation. 



In glycerin broth alkali is produced 

 until original acidity has been 

 neutralized, terminal reaction al- 

 kaline. 



After isolation bacUli are shorter and 

 plumper than the human type. 

 After cultivation they stain evenly. 



Are highly pathogenic for cattle, 

 causing generalized tuberciilosis, 

 which usually terminates fatally. 



0.01 mgr. of surface growth injected 

 intravenously into rabbits causes 

 progressive generalized tubercu- 

 losis, terminating fatally in forty- 

 five to sixty days. 



Guinea-pigs highly susceptible; gen- 

 eralized tuberculosis after injec- 

 tion. 



Human. 



Growth is raised, wrinkled, dry; ad- 

 heres tenaciously to the medium; 

 diffuses with difficulty in NaCl 

 solution; growth luxuriant; pig- 

 ment formation marked. 



In glycerin broth alkah is produced 

 until acidity is nearly neutrahzed, 

 then acid increases until original 

 acidity is reached or exceeded. 



After isolation baciUi are longer than 

 bovine type, and after cultivation 

 stain unevenly. 



Pathogenicity for cattle sHght; tu- 

 berculosis local and recovery usual. 



0.01 mgr. of surface growth injected 

 intravenously into rabbits causes 

 either no lesions or lesions con- 

 fined locally to organs; never pro- 

 gressive tuberculosis. 



Guinea-pigs sKghtly susceptible; 

 tuberculosis usually localized, or 

 generalized only after several 

 months. 



There are many observations on record which seem to show 

 that there are transient forms between the two extreme types. 

 Park and Krumwiede state, after careful study of the evidence: 

 "Each type shows certain differences, the most important for 

 separation being those found culturally and in .virulence. The 

 great majority of cultures group themselves around two extremes, 

 from which there are a few cult\u-es showing variant character- 

 istics. There is no overlapping of characteristics. 



"These two types are probably different because of residence 

 in different hosts over long periods of time, and as such are stable. 

 The evidence in favor of rapid change of type is incomplete and 

 inconclusive." 



The authors explain reported findings by insufficient control 

 observations. Inoculation of human tubercle bacilli into calves 

 and repeated passage through calves had led some observers to 

 believe that the original human strain was converted into a 

 bovine strain. In these cases either virulence was increased, 

 with no correlation of changed culture characteristics, or when 

 culture characteristics were changed apparently a natural infec- 

 tion of the calves with bovine bacilli had existed so that mixed 

 cultures were obtained. In other cases cultures were studied 



