LACTATION 595 



milk is very slight, while in cow's milk it is practically absent 

 altogether. 



Bunge 1 has pointed out that whereas the inorganic salts in milk 

 are present in different proportions from. those found in the blood 

 plasma, these proportions are almost identical with those occurring 

 in the young animal. He supposes this similarity to indicate an 

 adaptation to the needs of the young. This point is illustrated in 

 the following table, which gives the respective amounts of mineral 

 constituents present in a hundred parts of ash of (1) the young pup, 

 (2) dog's milk, and (3) dog's serum. 



K2O 

 Na^O - 

 CaO 

 MgO 

 FeA - 

 PA 

 CI - 



Small quantities of oxygen, nitrogen, and carbon dioxide gases 

 have been found in solution both in human and in cow's milk. 



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 boiling. The char- 

 acteristic colostrum corpuscles have already been described. 



The mammary glands of newly-born animals sometimes secrete 

 small quantities of what is popularly called " witches' milk." This 

 secretion contains most of the constituents of normal milk, but the 

 solid substances are usually less in amount. It has an alkaline 

 reaction.^ 



' Bunge, LehrhiKh der Physiologischen wid Pathologischen Chemie, Leipzig, 

 1887, and various original papers. Cf. Abderhalden, "Die Beziehungeu der 

 Wachsthumsgescliwindigkeit der Sauglinge zur Zusammensetzung der Milch, 

 etc.," Zeitsoh. f. physiol. Gkem., vol. xxvi., 1899, and other papers by the same 

 author in the same journal (vols. xxvi. and xxvii.). For further references 

 see Lusk, The Science of Nutrition, Philadelphia, 1906. It is stated also that 

 the rennin of the stomach is specifically adapted for the coagulation of the 

 casein produced by the female of the same race. 



■^ 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, Eigen- 

 schaften und Veranderungen der Milch," Ergeb. der Phys., 1903, Jahrg. 2, 

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



