THE LACTOGENIC HORMONE 



may be more complex than in the female mammal. Third, 

 assay results in the pigeon can be expressed quantitatively 

 (weight of the crop glands), whereas, in the mammal, the 

 quantitative statement of the results of an assay is difficult 

 both because the results are more variable (the mechanism 

 of action is more complex) and because the measurement of 

 the results (e.g., the amount of milk secreted) is not feasible 

 except in large animals. If hypophysectomy has not been 

 performed, the pituitary of the mammal (probably more than 

 that of the pigeon) may also affect lactation. It is therefore 

 not surprising that the only satisfactory attempts to assay 

 the lactogenic hormone quantitatively have been made in 

 pigeons. A study of some of the factors affecting quantitative 

 assay in the pigeon will be found in the paper of Riddle, 

 Bates, and Dykshorn (1933). 



The effects of the lactogenic hormone on the gonads oj birds. ^ — 

 The administration of the lactogenic hormone to the mature 

 male pigeon is followed by a rapid diminution in the size of 

 the testes. No such effect, however, is produced in the ma- 

 ture male mammal (rat). In the mature female fowl (hen), 

 the parenchyma of the ovary, active or resting, is reduced as 

 a result of the injection of a lactogenic extract. Secondary 

 effects indicating a diminished ovarian secretion are also ob- 

 served (reduced size of oviduct and comb, diminished space 

 between pubic bones). These changes in the hen may be as- 

 sociated with the appearance of broodiness (see chap. iv). 



THE EFFECTS OF HYPOPHYSECTOMY ON LACTATION'^ 



Lactation cannot continue in the absence of the hypoph- 

 ysis. If the lactating mouse, rat, or ferret is hypophysec- 

 tomized, the secretion of milk ceases within approximately 

 24 hours. If the pituitary is removed from the pregnant 

 mouse, rat, or guinea pig, lactation of a few hours' duration 



■• Riddle and others (1933-35); Bates and others (1933, 1935). 

 5 Also see chap. ii. 



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