62 THE SECRETIONS: 



the fatty portion (cream) collects on the surface ; when boiled, 

 it becomes covered with a film of coagulated casein. My own 

 observations and those of others show that, when fresh, it has 

 always an alkaline reaction. D'Arcet and Petit have, however, 

 found it to be acid. This discrepancy may probably be explained 

 by the circumstance of the speedy conversion of the sugar into 

 lactic acid, which is sometimes noticed in cow's milk. The 

 state of acidity is hastened by a heightened temperature, and 

 is most rapidly induced by being brought in contact with rennet. 

 The specific gravity of cow's milk varies from 1030 to 1035. 



We possess several analyses of cow's milk ; it has been exa- 

 mined by Herberger and myself by the method I have pre- 

 viously explained, and our results approximate closely. The 

 third of my analyses (No. 82) represents the milk a short time 

 after calving, while it still retained the character of colostrum. 

 Boussingault and Le Bel have also analysed normal milk with 

 the view of ascertaining the influence of various sorts of fodder 

 on its composition ; by the adoption of the French method to 

 which I have already alluded, they obtained too little casein 

 and too much sugar. I shall give the mean of twelve of their 

 analyses : 





g "C 



3 g 



An.80. 81. 82. 1. 2. 1 3 1 



Water . . 857'0 861-0 823-0 853-0 862-0 868 874-0 870-2 



Solid constituents . 143-0 139-0 177'0 147-0 138-0 132 126-0 129-8 



Butter . . 40-0* 38-0 55-0 38-9 37-5 36 39'0 31-3 



Casein . . 72-0 68-0 67-0 69'8 67'0 56 34-0 44-8 



Sugar and extractive 1 2g . Q 2g>() 51 . Q M . 3 ^ ^ 



matter . . j > 40 



Fixed salts . 6-2 6-1 13-0 7-0 7-2 J 6-0 

 Earthy salts . 2-2 



[Haidlen found, in the milk of a cow : water, 873 ; solid 

 residue, 127; butter, 30; casein and insoluble salts, 51; sugar 

 and soluble salts, 46. He has carefully studied the salts of 

 the milk, and is of opinion that the carbonate of soda that 

 occurs in the ash does not originate from a lactate in the fresh 

 milk, but exists there combined with casein. The salts are 

 combinations of phosphoric acid with lime, magnesia, and per- 



