PHYSIOLOGICAL 



did before ovulation. But the yellow body instead of containing 

 fluid is filled with tissue. The fate of this yellow body (which 

 is called technically the corpus luteum) depends upon whether 

 or not the cow has become pregnant. The presence of the 

 foetus in {he uterus reacts upon the corpus luteum and causes 

 it to persist probably throughout the whole of pregnancy, and 

 possibly for some time beyond. If the cow does not become 

 pregnant the corpus luteum only lasts for two or three weeks, 

 and is in a state of degeneration before the return of oestrus. 

 These statements, however, are based rather upon an analogy 

 with other animals than upon direct observations upon cattle, 

 for which animals the records are all too scanty and very in- 

 sufficiently worked out. 



Recent research in all those animals which have been in- 

 vestigated has proved beyond doubt that the corpus luteum is a 

 very important organ, for not only is its period of duration 

 closely connected with the sexual rhythm, but the growth of 

 t;he milk tissue, and consequently the mammary function, is 

 dependent upon it. There is clear evidence that the corpus 

 luteum, apart from the rest of the ovarian tissue, elaborates an 

 internal secretion which passing into the blood reaches the cells 

 of the mammary glands, and directly stimulates these cells to 

 undergo growth and multiplication. Moreover the presence of 

 a fully developed corpus luteum in one or both of the ovaries 

 is correlated with an inhibition on the part of these organs to 

 produce ripe eggs. And so long as a functionally active corpus 

 luteum is existent in either ovary, oestrus cannot normally be 

 experienced, and ovulation cannot occur. It is clear, therefore, 

 that the period of duration of the corpus luteum is one of the 

 main factors in the recurrence of the short cycle which in the 

 cow is normally about three weeks. 



The period of persistence of the corpus luteum is known to 

 vary widely in different species of animals. It also varies in 

 different individuals, and, according to Williams 1 the well-known 

 American veterinarian, an hypertrophied or persistent corpus 

 luteum may be a cause of long continued sterility. Why the 

 corpus luteum should persist is not clear, but Williams states 



1 Williams, Veterinary Obstetrics, New York, 1909. 



