GENERAL PROPERTIES AND COMPOSITION 3 



Babcock pointed out a number of years ago that the chief 

 differences in the composition of normal milks are due to varia- 

 tions in the amount of fat, the milk plasma being fairly uniform 

 in all milks. The variation in the amount of serum solids in milk 

 from the same cow is rarely more than \ per cent., in milk from 

 different cows of the same breed usually less than i per cent, and 

 in milk from cows of different breeds not more than 2\ per cent.^ 



Statements have been somewhat frequently made to the effect 

 that each globule of milk fat possesses a capsule or membrane 

 composed of caseinogen, the rupture of which by churning, it was 

 supposed, enabled the fat to assume the form of butter. There 

 is now, however, considerable evidence in support of the view that 

 each fat globule by molecular attraction is surrounded by a more 

 closely adherent layer of caseinogen solution (milk plasma). 

 Bechamp holds that each globule is surrounded by a true mem- 

 brane. Storch, on the other hand, maintains that the membrane, 

 the existence of which he admits, is not a true capsule but a 

 gelatinous mucoid ground substance. The general consensus of 

 opinion among chemists is probably opposed to the view of 

 Bechamp, though further evidence is necessary before concluding 

 as to the exact nature of the layer around the fat globules. From 

 observation with the microscope it would appear that the fat 

 globules in milk are nearly always distributed unevenly in, and 

 not uniformly throughout, the plasma. It is, however, almost 

 impossible to examine milk quite naturally and this grouping may 

 arise from mechanical causes. 



The reaction of milk must be described on the whole as ampho- 

 teric. The milk of most animals is normally alkaline, but in the 

 carnivora fresh milk has an acid reaction. Normal acidity or 

 alkalinity in milk is due to the presence of acid or alkaline phos- 

 phates respectively, the amphoteric reaction to the presence of 

 both. The herds of cows which feed on certain grasses in various 

 parts of the world, such, for example, as the blue-grass region of 

 Kentucky, are found to give a slightly alkaline milk, and by 

 experiment it has been found that a ration of 10 lbs. a day of 

 sugar beets given to a cow will render her milk slightly alkaline. 

 As is well known, in a comparatively short time, owing to lactic . 

 acid or other fermentations, milk assumes a definitely acid reaction. 

 The specific gravity varies from 1028 to 1034 (average 1032). It 

 is approximately the same in cow's and human milk.- 



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Wisconsin Agricultural Experiments^ Bulletin 18 (1899), p. 34. 

 See also footnote on p. 154. 



