EXPERIMENT STATION BULLETINS. 357 



2. The associate bacteria may exert some influence upon the lactic bac- 

 teria in their relation to oxygen supply or other environmental conditions. 



3. There may be some relationship not at present indicated. 



B}' the work of Euling ', confirmed b}' C. Revis and G. A. Payne ^ who 

 claims that the casein in milk exists in the form of a tri-calcium phosphate 

 salt, some idea is obtained as to the real nature of casein in milk. This 

 compound is, however, understood differently b}' others, for Soldner^ dem- 

 onstrated the possibility of casein forming more than one salt with cal- 

 cium, and that the salt neutral in reaction was the probable form existing 

 in milk. He also believed that the calcium phosphate usually mixed with 

 casein precipitates was not chemical but a mechanical mixture. VanSlyke 

 and Hart * have confirmed the main results of Soldner, who, according to 

 their interpretation of his work, must have arrived at this conclusion in- 

 ferentially ^ Courant * mentions these casein salts of Soldner as tri- 

 calcium (basic) casein and di-calcium casein (neutral). Again, Lehman 

 and HempeP would make milk-casein a combination of calcium casein and 

 calcium phosphate. From the above evidence, it is safe to tentatively 

 conclude that calcium is combined with casein and perhaps this same calcium 

 anchors some acid radical in the formation of a salt. 



Besides the combining power possessed by casein for the inorganic con- 

 stituents of milk, (as calcium and phosphates, and perhaps other elements 

 or radicals,) there is a decided attraction on the part of casein for acids 

 formed in fermentation. This acid-combining property of casein has much 

 to do with the understanding of the nature of milk-souring, although it 

 may be no more significant than that exercised by the inorganic substance. 



Hammerstein^ regarded the union of casein and acid as non-chemical 

 because of its ready response to the action of water. Laxa® says that casein 

 combines with lactic acid to form lactates, but that these lactates do not 

 have the definite values ascribed to them by VanSlyke and Harf*, who 

 claim ''When casein or paracasein is treated with an acid in definite quan- 

 tities, we obtain compounds of definitely characteristic properties." This, 

 however, may mean the same as conveyed by Laxa who appeal's to convey 

 the idea that casein, under different conditions, is capable of combining 

 with different amounts of acid. This seems to be in accordance wdth the 

 statement of L. L. VanSlyke and D. D. VanSlyke* ^ "Casein takes up 

 acid from dilute solutions. For example, one gram of casein shaken with 

 100 cc. of N-1,000 hydrochloric acid for three hours, takes from the solu- 

 tion nearly 50% of the acid. The amount of acid thus taken up is not 

 definite and fixed, but varies (a) with the concentration of the acid, (b) with 

 the duration of contact until ec{uilibrium is reached, (c) with the tempera- 

 ture, and (d) with the kind of acid. Some acid is always taken up how- 

 ever small the amount of acid used; but the acid is never completely re- 

 moved from the solution however large the proportion of casein present." 



Wliile there may be some doubt as to the definite combinations of casein 

 and lactic acid, casein and calcium and perhaps phosphate, for our pur- 



iLandwirtsch. Versuchs-Stationen Bd. XXXI-5-403 (1885). 



2Journal of Hygiene, Vol. VII, No. 2, p. 219 (1907). 



3Landwirtsch. Versuchs-Stationen Bd. XXXV-5-351 (1888). 



".American Cliemical Journal, Vol. ?,S, p. 4(54 (1905). 



'•American Chemical Journal, Vol. 33, p. 467 (190oj. 



•iPflugers Arch.. 50-109 (1891). 



7Pflugers Arch.. 56-558 (1894). 



«Jahresbericht der Thierchemie Bd. VII p. 160. 



*Milch\virtschaftliches Zentralblatt, Bd. 1. p. 538 (1905). 



loAm. Chem. Jour., Vol. XXXIII, p. 494 (1905). 



"Tech. Bulletin No. 3. N. Y. .Agricultural Experiment Station (1906). 



