19 



there is a slowl}^ increasing alkalinity, which is first clearl}^ visible on 

 about the third to fifth da}". Toward the close of the first week, or 

 during the second week, a ver}^ slow separation of the casein (paraca- 

 sein?) takes place. The first visible separation is usually apparent 

 about the fifth to sixth or eighth to tenth day in the form of a 

 iiiillimeter-deep layer of clear whey on top of the milk, which is still 

 entirely fiuid. By the end of the third or fourth week the fine white 

 casein has settled so that it occupies onh' about one-half of the fiuid, 

 the supernatant whey being pale yellow and transparent. Above this 

 whey in old cultures there is always a 5 to 7 mm. wide, dense, bright- 

 yellow ))acterial rim on the tube. The casein does not set on the start 

 and is never coarse flocculent. It finally becomes packed together in 

 the bottom of the tube, but for a long time it consists of tiny separate 

 particles which roll over each other easily when the tubes are shaken. 

 This precipitated casein finally changes from white to yellowish and 

 is slowl}^ redissolved (peptonized). At no time during this precipita- 

 tion and re-solution of the casein is there any acid reaction or au}^ 

 formation of gas. The whey from such cultures had a slightl}^ bitter 

 taste. 



The reaction of the medium is best observed by adding to the milk 

 enough litmus water to make it a deep lavender color; i. e., 10 c. c. of a 

 saturated watery solution of c. p., blue, dry, lime-free litnuis to 200 c. c. 

 of milk. Man}' cultures were made in this medium with exact results. 

 During the first 8 or 10 days the blue color very slowly deepens and 

 the separation of the casein begins.^ During the next 10 days or so 

 the casein slowly settles and is still blue. Su))sequently the litnuis 

 becomes more or less reduced, but at no time is there any appearance 

 indicating the formation of any organic acid. When the litmus is not 

 reduced the whey is pale wine red Iw transmitted light (normal color of 

 the litmus), but is not red by reflected light. If after several weeks or 

 months of growth such reduced or partly reduced cultures are killed 

 by heating for 10 minutes at 56^ C, and are then exposed to the air 

 for some weeks, the color of the litmus returns. The undissolved 

 casein is now distinctly blue and the whey is not red ))y reflected light. 



Numerous tiny, white, centrally constricted, sheaf-like crystals of 

 tyrosin appeared in old milk cultures. Crystalline plates presumed to 

 be leucin also appeared. . 



Ps. camjpeHtrw and Px. jjhaseoli both act upon milk and litnuis milk 

 in much the same way. Neither produces any acid or gas. Both cause 

 a slowly increasing alkalinity in the milk with the separation of the 

 casein from the whey 1)}' means of a lab ferment. In both, a i)ortion 

 of this casein is redissolved (peptonized) with the formation of tyrosin 

 and leucin. I^a. stewarti^ on the contrary, docs not precipitate the 



L 



'In one iiistaiicc whey appeared in two tnlu-K of l)ln(' litmus milk tlic fourtli day. 

 See table uuiler lieduction. 



