564 THE PHYSIOLOGY OF REPRODUCTION 



The chief difference in the composition of cow's milk as 

 compared with human milk is the relatively high percentage of 

 proteins, fats, and salts, and the correspondingly low percentage 

 of lactose present in cow's milk. 



Colostrum is the milk which is secreted during the first two 

 or three days after parturition. It contains less caseinogen 

 than ordinary milk, but considerable quantities of albumen and 

 globulin enter into its composition. It coagulates on boiUng. 

 The characteristic colostrum corpuscles have already been 

 described. 



The mammary glands of newly born animals sometimes 

 secrete small quantities of what is popularly called "witches' 

 miUc." This secretion contains most of the constituents of 

 normal milk, but the sohd substances are usually less in amount. 

 It has an alkahne reaction.^ 



The Influence of Diet and other Factors on the 

 Composition and Yield of Milk 



The composition of the milk in any one species is subject to 

 some amount of variation, which is due to various causes. 

 Thus, the differences in the composition of cow's milk are said 

 to depend on the following factors : (1) The breed, (2) The 

 advance in the period of lactation, (3) The season of the year, 



(4) The length of the interval between the times of milking, 



(5) The occurrence of sexual excitement, (6) Situation and 

 chmate, (7) Meteorological changes, and (8) The character of 

 the food.^ These factors may now be briefly discussed. 



' For fuller information about the constituents and properties of milk, 

 with tables of composition for different animals, and numerous references to 

 the literature, see Halliburton, loc. cit. See also Eaudnitz, " Bestandteile, 

 Eigenschaften und Veranderungen der Milch," Ergeb. der Phys.. 1903, 

 Jahrg. 2, where certain later papers are referred to ; and Abderhalden, loc. cit. 



- Crowther, Milk Investigations at Garford, Leeds, 1904. Droop Rich- 

 mond, " The Composition of Milk," Analyst, vol. xxxi., 1906. Lauder, 

 "The Variation in the Composition of Milk," Bulletin XI. issued by the 

 Edinburgh and East of Scotland College of Agriculture, 1906. Crowther, 

 " The Chemical Composition of Butter," Trans. Highland andAgric. Soc, vol. 

 xix., 1907. Gilchrist and Jones, "Dairy Investigations in the North-East 

 of England," Trans. Highland and Agric. Soc, vol. xviii., 1906, and vol. 

 xix., 1907. 



