358 STATE BOARD OF AGRICULTURE. 



pose, quite a clear conception may be gained of the disappearance of traces 

 of lactic acid in the natural souring of milk. 



Laxa^ suggests that the lactic acid first formed combines with inorganic 

 substances of the milk, but also, almost immediately forms a lactate in com- 

 bination with casein. VanSlyke and Hart- says " ^\Tiere acid is formed 

 in cow's milk, or added to it, the acid first combines with the bases of the 

 inorganic salts of the milk and then with the calcium resulting in the forma- 

 tion of a precipitate which is free casein." 



"By further formation or addition of acid, the free casein unites with it, 

 forming a casein salt of the acid, this compound, in the case of lactic acid, 

 being the coagulum familiar in the ordinary souring of milk." 



Revis and Payne^ claim "The compounds of calcium salts and of lactic 

 acid with casein as the}' occur in milk, do not possess the definite compo- 

 sitions of those that have been formed with casein after its separation from 

 milk, as described by Soldner for lime salts, and Van Slyke and Hart for 

 lactates of casein, but that the proportions of tri-phosphates and lactic 

 acid in combination with the casein are at any moment before the milk 

 coagulates, the result of a sort of equilibrium between the casein and total 

 lactic acid present, and that at the moment of precipitation of the casein, 

 the calcium tri-phosphate has been practically completely eliminated, and 

 the combination with lactic acid has reached a maximum." 



This cursory consideration throws some light upon the possible changes 

 taking place during the formation of lactic acid. 



There are inorganic salts apparently in loose combination with casein 

 besides the inorganic salts naturally in solution. These may respond to 

 lactic acid in forming neutral lactates untouched b}' the usual titrating 

 methods, and thus account for the seeming delay in the formation of acid 

 until the lactic micro-organisms have reached a certain number, somewiiere 

 in the hundreds of millions per c. cm. With the introduction of the asso- 

 ciate element, either the lactic micro-organisms are stimulated by the forma- 

 tion of definite products due to the growth or increase of the associate germs, 

 or possibly, on the other hand, these products liberate or make recognizable 

 earlier in the process, the acid manufactured by the lactic micro-organisms. 

 Both considerations may be applicable, since the increase in acid in the 

 combination does not always seem attributable to the same cause. 



There is also in alcohol fermentation a stage, at the beginning or for a 

 period after inoculation, in which the only visible signs of anything trans- 

 piring are found in an increase of the j-east content. After fermentation 

 sets in, progress is rapid. At this time wiien fermentation is most active 

 zymase may be most advantageously extracted by Buchner's method. 

 This does not answer, however, what relation the yeast cells have to fermen- 

 tation during the period of quiescent growth, and during which very little 

 if any zymase may be detected; the period is short, when no fermentation 

 changes can be detected. 



Is it true that enzymes are not manufactured or that fermentative changes 

 do not take place before the micro-organisms foresee the end of their in- 

 crease in the medium and that any influence or agent which will reduce the 

 time necessary to reach this point, makes the process shorter, whether it 

 is temperature, oxygen supply, reaction, pabulum or the influence of an 

 associate germ? If so, then an associate influence may be nothing more 



1 Milch wirtschaft Zentralblatt. Bd. I. p.. 358. 



•■'Am. Jour., Vol. 33, p. 495 (1905). 



sjournal of Hveieno, Vol. VII, No. 2, p. 231 (1907). 



