198 PHYSIOLOGY OF FARM ANIMALS [CH. 



In vie^\ of these and other facts it seems certain that the 

 ovaries are organs elaborating internal secretions which change 

 both in character and quantity during the successive phases of 

 the oestrous cycle, and that these secretions are resj)onsible for 

 the various processes which recur rhythmically in the uterus and 

 mammary glands. During the anoestrum the ovarian secretions 

 suffice to preserve the normal nutrition of the uterus and to pre- 

 vent that organ from laj^sing into the infantile condition. During 

 the prooestrum and oestrus they stimulate the uterine and 

 mammary tissues to undergo some amount of growth. But it is 

 not until the corpus luteum is formed that the ovary acquires 

 its maximum influence upon the accessory generative organs and 

 maanmary glands which then undergo the extensive anabolic 

 changes without which the young could not obtain the nounsh- 

 ment which is necessary for their growth and development. 



Schafer and others have shown that extracts of corpus 

 luteum and j)osterior lobe of pituitary during lactation have a 

 galactogogue influence upon the mammary glands causing an 

 instant and copious secretion of milk. These observations further 

 emphasise the functional connection between these organs and 

 the milk glands, but it is possible that the sudden injection of 

 these extracts in considerable quantity has a somewhat different 

 and more violent effect than the slow passage of the proble- 

 matical hormones into the circulation, such as one may presume 

 to occur in nature. Moreover it may be that this building up of 

 the mammary tissues is a process not essentially different from 

 that concerned in milk secretion but that the two phenomena are 

 in reality parts of a process of the same nature throughout (that 

 is to say, it is not necessary to regard them as representing two 

 opposing tendencies, one anabolic and the other katabolic)^. 



It is known that double ovariotomy results in the hypertrophy 

 of the pituitary gland, and also that double ovariotomy during 

 lactation leads to almost indefinite continuation of milk secre- 

 tion, and it seems not improba])le that these two facts are con- 

 nected. Furthermore, it is conceivable that the hypertrophied 

 pituitary compensates for the absence of the corjDus luteum, and 

 that unlike the latter organ, persists for a very extended period 



1 Apart however from these factors the removal of the secretion in sucking 

 or milking is necessary for continued lactation, and a cow whose milk is not 

 withdrawn very soon becomes dry. 



