LACTATION 621 



glands. It would seem possible that the guinea-pig may differ from 

 the rabbit in this respect, or more probably that under certain 

 conditions glandular elements in the ovary, other than corpora 

 lutea, may take over the function of the latter organs. In this 

 connection it may be recalled that according to Loeb the primary 

 growth of the mammary glands takes place before ovulation, and 

 the main or secondary growth is postponed until a later phase 

 when the corpora lutea have been in existence for some time. 



It has been shown that extract of corpus luteum has a marked 

 galactogogue effect, intravenous injection resulting in an immediate 

 outpouring of milk. This was first demonstrated by Ott and Scott ^ 

 in the goat and has since been confirmed for man and other animals 

 by Sharpey Schafer,* and Mackenzie,^ arid Gavin.* Ott and Scott were 

 the first to show also that extract of posterior lobe of pituitary gland 

 had an even more marked result. Extracts of placenta, involuting 

 uterus, and pineal gland were similar, as well as the lactating gland 

 itself. According to Hammond^ the pituitary and other extracts 

 probably act directly on the gland-cells, and it seems certain that 

 more milk may be drawn off than could have been present in the 

 sinuses and ducts at the moment of injection. The extract, there- 

 fore, must cause the glands to secrete. Sharpey Schafer,^ however, 

 is of opinion that the hormone acts on the unstriated muscle cells 

 in much the same kind of way as extract of pituitary or corpus 

 luteum causes contraction of the muscle of the uterus. Sharpey 

 Schafer states further that the ovary appears to secrete two 

 excitants, one increasing the contractility of muscle, the other 

 inhibiting it. 



Simpson and Hill,' however, differ from Sharpey Schafer and 

 point out that barium chloride, which is a specific stimulus for 

 muscle, has no eifect on the milk flow. 



It is probable, therefore, that the corpus luteum is normally an 



1 Ott and Scott, "The Galactogogue Action of the Thymus and Corpus 

 Luteum," Proc. Soc. Exp. Biol, and Med., vol. viii., 1910. See also 'Ott's 

 Contributions to Physiology, Part xix., 1912. 



2 Schafer and Mackenzie, " The Action of Animal Extracts on Milk Secre- 

 tion," Proc. Roy. Soc, B., vol. Ixxxiv., 1911. 



3 Mackenzie (K.), " An Experimental Investigation of the Mechanism of Milk 

 . Secretion," Quar. Jour. Exp. Physiol., vol. iv., 1911. Hill and Simpson, 



" The Effect of Pituitary Extract on Milk Secretion in the Goat," Qv/xr. Jour. 

 Exp. Biol., vol. viii., 1914. See also Amer. Jour, of Physiol., vol. xxxv., 1914, 

 and Proc. Soc. Exp. Biol, and Med., vol. xi., 1914. 



* Gavin, " On the Effects of Administration of Extracts of Pituitary Body 

 and Corpus Luteum to Milch Cows," QvMr. Jour. Exp. Physiol., vol. vi., 1913. 



5 Hammond, "The Effect of Pituitary Extract on the Secretion of Milk," 

 Quar. Jow: Exp. Physiol., vol. vi., 1913. 



^ Sharpey Schafer, The Endocrine Organs, London. 



' Simpson (S.) and Hill, " The Mode of Action of Pituitary Extract," Quar. 

 Jow- Exp. Physiol., vol. viii., 1915. See also Schafer's Note to this paper. 



