152 Studies in Milk Secretion 



It will be seen that the effect of adrenalin injections is to reduce the 

 rate of milk secretion for the period following that of injection but it 

 has no marked immediate effect on the mammary gland. It is quite 

 possible that the suprarenals produce in the body at times large quantities 

 of adrenalin. Cannon, Stohl, and Wright^ have found that glycosuria 

 is produced after great excitement or severe fright and this is probably 

 due to increased secretion of adrenalin. It is a well-known fact that 

 cows give less milk under these circumstances. This fact has hitherto 

 been cited as showing that the nervous system has some action on 

 mammary secretion, although investigators have always failed to 

 demonstrate the existence of nerves controlling mammary secretion. 



It is interesting to compare the effects of pituitary extract and 

 adrenalin; both cause contraction of involuntary muscle, hyper- 

 glycaemia and glycosuria, but pituitary extract alone has the immediate 

 effect of augmenting milk secretion. The main difference in their action 

 is that adrenalin acts only in connection with the sympathetic nervous 

 system and pituitary extract acts generally. 



Although the effect on milk secretion immediately obtainable after 

 injection of pituitary extract is not brought about by adrenalin, the latter 

 substance produces the same after-effects, due perhaps to the loss of 

 sugar by glycosuria. Experiments with phloridzin described in the 

 previous paper show also that anything disturbing the sugar meta- 

 bolism of the body at once affects milk secretion. 



Conclusions. 



I. The flow of milk produced as a result of an injection of pituitary 

 extract varies with the state of nutrition of the injected animal. 



II. This variation (due to nutrition) is not so great as that produced 

 in the case of the morning or the daily yields, indicating that the action 

 of the pituitary extract is on some more stable (storage) quantity. 



III. The percentage fat of the pituitary milk is increased by the 

 state of lowered nutrition in the same way as that of the normal milk. 



IV. Injections of adrenalin though resembling pituitary extract in 

 causing hyperglycaemia differ from them in having no immediate 

 action on milk secretion. 



V. Injections of adrenalin have a secondary effect on milk secretion 

 causing a decrease in the amount of milk produced for a period of a 

 day following its injection. 



^ Amer. Jour, of Physiol. Vol. xxix, 1912. 



