THE PHYSIOLOGY OF LACTATION 



The complex nature of milk has long aroused man's curiosity, 

 and several speculations have been handed down to us by ancient 

 philosophers. Empedocles, for instance, considered milk as 

 "white pus," a view which recalls statements made by several 

 modern authors, who have regarded milk secretion as the result 

 of a pathologic process, evidenced by the presence of large numbers 

 of leukocytes in the early product of the mammary glands. Aris- 

 totle thought that milk consisted of "parboiled substances from 

 the blood." He reasoned that milk originated from the same 

 food material that served to nourish the fetus, a view entertained 

 today. Pfaundler— a modern investigator — defines milk as "the 

 product of adaptation of the maternal system to the fetus." The 

 fetus withdraws food in increasing quantity from the mother and 

 the maternal system responds to this loss of substance by overpro- 

 duction, a theory similar to the overproduction theory of Weigert. 

 After birth the mother continues to produce these food substances, 

 which are then transformed by the mammary glands into milk — 

 the food for the newborn. 



Milk is the characteristic production of mammals, but there 

 are marked differences between the milks of various species. 

 The fundamental substances — protein, milk-sugar, fat, and mineral 

 matter — resemble each other, but their quantitative relation is 

 not the same. The fat content especially is greater in some milks 

 than in others, while protein, sugar, and mineral matter vary in 

 lesser degree. The differences are both quantitative and quali- 

 tative. The mother furnishes the food to the young as the latter 

 demands it, and we can understand, therefore, why the composi- 

 tion of milk should be particularly adapted to the nourishment of 

 the young mammal. The milk of mammals which require Istrge 

 heat energy contains much fat; for example, in the milk of the 

 whale and dolphin the fat makes up about one-half of the fluid. 

 In any case, milk is a perfect food for early life, and since each 

 mammal has characteristic requirements the substitution of 

 milk from one species for milk of another may bring disappoint- 

 ing results unless special precautions are taken, such as cleanly 

 production and suitable modification. 



Pfaundler suggests the idea that milk may be regarded as an 

 antibody elaborated by the maternal system in response to the 

 introduction of a foreign body, meaning the spermatozoa. Ac- 



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