4vv Bulletin 167 



took on a dark rich amber color and reacted distinctly alkaline 

 to litmus. 



Potato blocks. — Cultures upon cooked potato blocks showed 

 a persistent growth which was moderate in amount, echinulate. 

 often spreading at the base ; convex with a glistening luster, con- 

 toured surface, and slimy to butyrous consistency. The tubes 

 gave off a characteristic odor suggestive of alcohol, and gas pro- 

 duction was noted. The medium was grayed. 



Milk. — Tubes of fresh centrifuged milk inoculated with a 2 

 mm. loop of 24 to 48 hour old broth cultures held at 25 ° C. 

 showed no visible change for 4 to 6 days. Thereafter coagula- 

 tion occurred with gradual shrinking of the curd and extrusion 

 of whey, accompanied by gas formation. The same changes were 

 observed both at 20 and at 30° C, but the process was always 

 slower at the lower temperature and more rapid at the higher. 

 The coagulum was firm and leathery, becoming slightly yellowish 

 by reflected light. Tubes held under observation for 2 months 

 showed yellowish translucent spots which suggested slight pep- 

 tonization, but they were believed to result merely from shrink- 

 ing of the curd. (See production of proteolytic enzyms, pages 



509)- 



Acid production in milk. — This was determined in the fol- 

 lowing manner : Freshly drawn milk was centrifuged, then 

 further freed from fat by filtering through several thicknesses of 

 filter paper, carefully pipetted into tubes, 10 cc. in a tube, steril- 

 ized by discontinuous steaming on 3 consecutive days, and in- 

 oculated with a 2 mm. loop from young broth cultures. Titra- 

 tions were made at the end of 1,2, 4, 10, and 20 days, respectively. 

 For this purpose the content of the tube was added to 40 cc. of 

 distilled water, the mixture boiled for 1 minute and at once 

 titrated against phenolphthalein with N/20 sodium hydroxid. The 

 acid production was calculated by subtracting from the reaction 

 of the inoculated tube the average reaction of all check tubes in 

 the same scries and averaging the differences thus obtained. 



