THE PITUITARY BODY 



however, by distending the emptied uterus with an inert sub- 

 stance like paraffin. The observations of Nelson (1933-35) 

 were made in guinea pigs. He found that the removal of the 

 ovaries of a pregnant guinea pig was not followed by lactation 

 unless the uterus was also removed or until abortion or 

 parturition had occurred. The removal of the pregnant 

 uterus of the guinea pig was not followed by lactation (unlike 

 the mouse). Cesarean section — of the fetuses only — was not 

 followed by lactation until after the later expulsion of the 

 placentae. Nelson also found that a purified galactogenic ex- 

 tract of the anterior lobe did not cause lactation in the preg- 

 nant guinea pig. The foregoing experiments in pregnant and 

 non-pregnant mice and rats suggest that the uterus may in- 

 fluence (inhibit) the secretion of the lactogenic hormone of 

 the pars glandularis, although an effect on the breasts cannot 

 be excluded. In the pregnant guinea pig, the ovaries and the 

 uterus may both be interrelated in exerting such an inhibi- 

 tory control. 



3. Suckling as a factor. — Selye, CoUip, and Thomson 

 (1934) concluded that the act of suckling influences the secre- 

 tion of the lactogenic hormone. In lactating rats, they tied all 

 the main galactophores of the breasts on one side, and excised 

 the nipples on the other. Suckling at the breasts from which 

 no milk could escape maintained lactation in all the breasts 

 beyond the time when lactation ceases in normal rats due to 

 weaning. Suckling may initiate lactation in the pseudo- 

 pregnant rat.'^ 



4. Observations in parabiotic animals.^^ — In the experiment 

 9 9 p, the hypertrophy of the breasts of the normal female 



rat may be nearly as great as that of pregnancy. '^ Such a de- 



'3 Also see Selye and McKeown (1934); and JefFers (1935). 



M 9 or ? indicates a normal or a spayed female; 9p, indicates a pregnant fe- 

 male; d^ or sT, indicates a normal or a castrated male. 9 9 p, indicates parabiosis 

 between a normal female and a pregnant female, and so on. Also see chap. iv. 



'5 The oestrous cycles of the normal female may be almost completely suppressed. 



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