THE ACID-PROOF BACTERIA. 367 



by no means lessened by the fact that under these cir- 

 cumstances they are always numerically in the minority. 

 When present in butter, their isolation offers fewer diffi- 

 culties, for by the injection of the butter containing 

 them into the peritoneal cavity of guinea-pigs conditions 

 are created that favor their development, and from ani- 

 mals so treated they may usually be recovered in pure 

 culture. 



When studied in pure culture, all of them are at once 

 distinguished from bacillus tuberculosis by the follow- 

 ing group characteristics : they are of relatively rapid 

 growth, there being usually an abundant development 

 on glycerin agar-agar after twenty-four to forty-eight 

 hours at body-temperature ; they grow well but less 

 rapidly at ordinary room-temperature /. <?., at 18 to 

 20 C. ; they grow well in litmus-milk, and, as a rule, 

 produce alkali that causes the color to become a deep 

 blue ; the growth on agar-agar is dry, shrivelled, and 

 wrinkled in appearance, and of a soft, mealy consistency 

 in some cases (Holler's grass bacillus II., Rabinowitsch 

 butter bacillus, for instance), while in others it is more 

 membranous, as in the case of Holler's timothy bacillus. 

 We have never seen in these cultures the hard, coarse 

 granules so common to cultures of bacillus tuberculosis ; 

 on glycerin agar-agar some of them, namely, the timothy 

 bacillus of Holler and its varieties, grow with a distinct 

 orange color, while others, the grass bacillus II. of 

 Holler, the butter bacillus of Rabinowitsch, and their 

 closely allied varieties, begin as a grayish-white deposit 

 which may ultimately become of a pale or even distinct 

 salmon color. 



When pure cultures of them are injected into such 

 animals as rabbits or guinea-pigs, some of them have no 



