CHAPTER VI 



THE EFFECTS OF HORMONES OF THE 



PITUITARY BODY ON THE 



SECRETION OF MILK^ 



THE first hint that a hormone of the pituitary body 

 might affect the secretion of milk came from the 

 experiments of Ott and Scott (1910). They found 

 that an increased amount of milk could be withdrawn from 

 the udder of the lactating goat immediately after the intra- 

 venous injection of an extract of the pars neuralis. Extracts 

 of the pars neurahs, however, are probably not truly lacto- 

 genic; rather, they seem to cause an emptying of the milk- 

 distended alveoli and ducts without furthering the secretion 

 of milk. More important was the report of Strieker and 

 Grueter (1928) that lactation could be produced in the 

 pseudopregnant rabbit, before or after spaying, by the injec- 

 tion of an extract of the pars glandularis. Moreover, by 

 means of similar treatment, they caused a resumption of 

 lactation in a doe and a bitch, both of which had secreted no 

 milk for 10 days or more. The work of Strieker and Grueter 

 has been confirmed and extended by a number of investiga- 

 tors. 



Lactation cannot occur in the hypophysectomized ani- 

 mal.^ Beyond this statement, it is difficult to make general- 

 izations either because various mammals differ in the mech- 

 anism of lactation or because our knowledge of the controlling 

 factors is deficient. At least the later stages of the growth 

 and differentiation of the breasts appear to depend upon the 



' Also see p. 199, chap. v. 



^ Except in animals (e.g., rats) hypophysectomized during pregnancy. After 

 parturition, lactation of only a few hours' duration sets in. 



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