586 Scientific Proceedings, Royal Dublin Society. 



It has been shown that the secretion of milk in cows is increased by the 

 absorption of the extract of certain other organs of the body, 1 for instance, 

 the pituitary gland and the corpus luteum. These substances temporarily 

 increase the quantity both of milk and butter-fat, and what can be shown to 

 take place experimentally no doubt happens in the normal working of the 

 body. Admitting the action of these hormones on the mammary gland, and 

 recognizing that the daily variation in total fat-yield is not similar to that of 

 the other milk constituents, it appears that those hormones which influence 

 the production of fat are not identical with those which affect the production 

 of the other constituents of the milk. Professor Wilson 2 has shown that the 

 factors for the quantity and quality (fat) are separately inherited. It is 

 possible that extract of pituitary gland or corpus luteum contains different 

 hormones which have various effects, and it is probable that there are other 

 organs in the body which contribute to the blood a substance or substances 

 which, when conveyed to the mammary gland, influence its production 

 of some or all of the constituent substances of milk. The quantity of the 

 hormones liberated depends on the activity of the secreting glands, and since 

 this is regulated by the general tone of the body — a variable factor — the 

 quantity and, perhaps, the quality of the product vary. The liberation of 

 these substances in varying quantities according to the cow's condition would 

 account for the daily variation of milk and butter-fat. 



The question then arises as to the relative activity, during successive 

 periods, of the mammary gland, because of the apparently anomalous pro- 

 duction of practically as much butter-fat after nine hours as after fifteen 

 hours. This fact seems to suggest that the gland is more active during the 

 shorter period. If that were so it would be advisable to draw the milk from 

 cows several times during the twenty-four hours, and always after short 

 intervals ; but in practice it is found that frequent milkings do not materially 

 increase the yield. More milk can, however, be obtained from animals which 

 are milked several times a day than from those which are milked only once ; 3 

 but this can be accounted for by the injurious effects on the cow of the 

 pressure from a large store of milk in the udder for such a long time. An 

 explanation of the apparent varying activity of the gland during successive 

 periods of the day must, therefore, be sought elsewhere. 



'Chapter on "Lactation" in "The Physiology of Reproduction," F. H.Marshall, 

 1910. Proc. Soc. Exp. Biol, and Med., vol. viii, No. 2, 1910. Proc. Royal Society, B, 

 vol. lxxxiv, 1911. Gavin : Quarterly Journal Experimental Physiology, vol. vi, 1913. 

 Ibid., vol. vi, 1913, Schafer. Ibid., vol. vi, 1913, Hammond. 



2 " The Separate Inheritance of Quantity and Quality in Cows' Milk," Wilson: 

 Scientific Proc. Royal Dublin Society, July 29th, 1910. 



3 Kellner : "The Scientific Feeding of Animals." London, 1909, 



