Wm. R. Lyons 325 



progesterone, and the same protein. In all our experiments the importance 

 of the two ovarian hormones in stimulating prolactational mammary growth 

 has been demonstrated. None of the well-identified pituitary hormones is at 

 present suspected of being able to stimulate directly the growth of the mam- 

 mary gland except the lactogenic. We have been able to stimulate "local" 

 lactational growth in individual mammary glands (or sectors) in rabbits in- 

 jected intraductally with pure lactogenic hormone. But it seems likely, judg- 

 ing by the experience of most investigators, that the direct mammotrophic 

 action of the lactogenic hormone is only possible in the hypophysectomized 

 animal restored toward normalcy by certain of the depleted "target-organ" 

 hormones, as for example, adrenocortical hormone. 



Conclusions 



I. In female rats hypophysectomized at 60-70 days of age and treated imme- 

 diately thereafter, the following types of mammary development were ob- 

 served after daily injections for ten days of the hormones listed: 



A. Regression to a gland showing bare ducts after: 



(1) 5-10 I.U. of estrone 



(2) 1 I.U. of progesterone 



(3) 10 I.U. of estrone plus 1-2 I.U. of progesterone 



(4) A pituitary FSH which stimulated the ovaries and produced estrous 

 uteri and vaginae 



B. Maintenance of an apparently normal duct system bearing sparsely dis- 

 tributed alveoli and alveolar buds after: 



(1) 60-120 I.U. of pvnified lactogenic hormone 



C. Incomplete lobulo-alveolar growth after: 



(1) 60 I.U. of purified lactogenic hormone plus 10 I.U. of estrone 



(2) 60 I.U. of purified lactogenic hormone plus 5 R.U. of FSH 



(3) 5 and 1 o mg. of a crude lactogenic hormone (also containing adieno- 

 trophin and somatotrophin) 



D. Complete lobulo-alveolar growth after: 



(1) 5 mg. of a crude lactogenic extract also containing adrenotrophic 

 and somatotrophic hormones, plus 10 I.U. of estrone 



(2) 5 mg. of the same crude lactogenic extract plus 5 R.U. of FSH 



II. In female rats hypophysectomized and oophorectomized at 60-70 days of 

 age and treated immediately thereafter, the following types of mammary de- 

 velopment were observed after daily injections for ten days of the hormones 

 listed: 



A. Maintenance of an apparently normal duct system, bearing sparsely dis- 

 tributed alveoli and alveolar buds after: 



(1) 5 mg. of the above-mentioned crude lactogenic extract plus lo I.U. 

 of estrone 



(2) 5 mg. of the same crude lactogenic extract plus 5 R.U. of FSH 



