MAMMARY GLANDS IN EKDOCRIN RELATIONSHIPS 647 



in part act as a stimulus to the pubertal mammary growth, since he found 

 that ovarian castration followed by testicular implants did not inhibit the 

 development of the mammae at puberty. Opposed to this conception is 

 the fact that the injection of testicular extracts by Fellner gave indecisive 

 results as regards the growth and secretory activities of the mammae, and 

 MacKenzie obtained negative results as regards milk secretion in similar 

 types of experiments. These investigations open up wide fields for study 

 and speculation, being as they are so intimately connected with funda- 

 mental biological principles. 



Mammary Gland Extracts as Galactago^ues 



In the search for substances acting as stimuli to lactation, many and 

 varied tissue extracts have been employed, some of which have been 

 found to have a marked excitatory action on mammary secretory function. 

 As a result of the injection of a saline extract of mammary tissue into 

 cats, MacKenzie frequently, but not always, obtained augmented milk 

 secretion. In view of this fact it would be interesting to determine 

 whether or not the presence or absence of the stimulating substance is in 

 any way dependent upon the degree of development or relative activity 

 of the gland from which the extract is made. 



In this connection it should further be mentioned that Wilms has 

 obtained an abundant secretion of milk in a mother whose lactation was 

 scanty, by the administration of several successive hypodermatic injections 

 of 3-15 minims of her own milk. This observation raises the question as 

 to whether or not the stimulating substance is the same as that found by 

 MacKenzie in extracts of mammary gland tissue. 



The Hypophysis as a Stimulant to Lactation 



The credit for first putting on record the fact that extracts of the 

 posterior lobe of the hypophysis, when injected hypodermatically into 

 animals, produce an increased rate of milk secretion belongs to Ott and 

 Scott (a) ; these investigators worked with goats. Schafer and MacKenzie 

 later demonstrated that not only pars posterior, but also the pars inter- 

 media extracts act as stimulants to lactation. It is to be regretted that 

 we do not yet know whether or not one of the normal functions of this 

 gland is that of initiating and assisting in the regulation of the flow of 

 milk, or whether this galactagogic action is accidental rather than pur- 

 poseful. The fact that extracts derived from the fish stimulate milk flow 

 may be not without significance in this regard. 1 



1 It should be added that results obtained in Carlson's laboratory and elsewhere 

 show that the augmentation of milk flow is due merely to action of the extract on the 

 muscular tissue of the gland. No actual increase in milk production has been demon- 

 strated. R. G. H. 



