DAIRY FARMING DAIRYING. 185 



DAIRY FARMING— DAIRYING. 



Some points in the physiological chemistry and coagulation of 

 milk, D. F. HARRIS (Proe. Roy. Soc. Edinburgh, 21 (1895-1897), pp. 72- 

 89). — The author studied the physical-chemical condition of caseinogen 

 in milk, the chemistry of the coagulation of caseiuogen, the chemistry 

 of casein, the digestion of milk, etc. He uses the term caseinogen to 

 mean casein as if exists naturally in the milk, before it is coagulated. 

 With reference to the caseinogen he concludes that — 



" Caseinogen is not, in the ordinary acceptation, in solution in milk plasma. It is 

 in the most intimate association with the fat; in all probability the particles consist 

 of fat in direct ratio and of caseinogen in indirect ratio to their bulk. In this sense 

 caseinogen is 'particulate.' 



"The arguments that caseinogen is present as an envelope are still entitled to 

 respect; but there is some evidence pointing to this proteid being interstitiallv asso- 

 ciated with the fat. 



"Both the clots and precipitates in milk and in 'pure' caseinogen are more or lees 

 cohesive agglutinations of the preexisting particles; there is no trace of fibrous 

 structure. 



"The so-called 'pure solutions' of caseinogen are suspensions of particles upon 

 whose presence depends their coagulability, in which respect they resemble diluted 

 milk or concentrated whey. Their pressure-filtrates contain no proteid." 



The author's experiments confirm Ringer's view that the coagula- 

 tion of casein is a twofold process, the first stage being the conversion 

 of caseinogen by rennet into a soluble form of casein, which he calls 

 procasein; and the second stage, the precipitation or solidification of 

 this procasein into a more or less cohesive clot or curd (casein). 



By analyses of acetic-acid whey and rennet whey the author shows 

 that " there is some chemical difference between the precipitation of 

 caseinogen by an acid and the clotting of it by rennet — a difference 

 able to be expressed, at least, in terms of the union of calcic phos- 

 phate. Some call this clot a caseate of calcium. Normally in milk it 

 may be so." 



The effect of various salts on the curdling of milk was studied, and 

 the curdling of milk from which the lime had been removed by precipi- 

 tation with potassium oxalate and centrifugal force, using decalcified 

 rennet. 



"Only the soluble salts of calcium, barium, and strontium can precipitate pro- 

 casein. They are concerned only with the second stage of clotting. . . . 



"One factor in the inhibition of clotting by certain potassium salts is the high 

 alkalinity. 



"The absence of lime is a more powerful inhibitant than the presence of potash." 



The experiments with artificial digestion of milk which had received 

 different treatment lead to the following statements: 



'My experiments with milk mixed with water tr with CaH e O:, in order to render 

 it more digestible, as it is alleged, tend to show that this property is entirely due to 

 the greater laxity of the clot which forms when the solid particles of milk are, from 

 any cause, separated from one another. Evidently the power of rennin for binding 



