The Corpus Luteum of Pregnancy 121 



non-pregnant. When a typical corpus luteum of pregnancy 

 is present and other findings are in accord, the evidence it 

 affords is of the greatest possible value. Amongst thousands 

 of ovaries which I have examined, I have seen but one cor- 

 pus luteum of pregnancy which departed markedly in volume 

 from the normal. The one exception was more than one inch 

 in diameter. In cows which, though pregnant, nevertheless 

 show estrum, the corpus luteum disappears, at least some- 

 times. Hence a cow may be pregnant and no corpus luteum 

 present. 



The corpus luteum of pregnancy persists throughout 

 pregnancy and for thirty to sixty days after its close. The 

 corpus luteum of estrum is a temporary structure, which be- 

 gins to disappear rapidly at about eighteen days after es- 

 trum, so that at the average period of twenty-one days it has 

 become so far resorbed that it no longer inhibits the matur- 

 ing of a fresh ovisac. 



It is at this period that the corpus luteum becomes of 

 special significance in the diagnosis of very early pregnancy. 

 If estrum has been regular and the animal is not pregnant, 

 it is very certain that at about twenty-one days the animal 

 will again be in estrum and that the corpus luteum of the 

 previous estrum will have decreased to a small size. At the 

 same time, if estrum is near, the uterus is engorged, the 

 cervical canal is dilated, and the vagina contains the lubri- 

 cant mucus of estrum. Hence, if the practitioner examines 

 a cow at about eighteen to twenty-one days after breeding, 

 if she is pregnant, there is almost invariably a typical corpus 

 luteum ; if she is not pregnant, the corpus luteum is definitely 

 atrophied. This is one of the best times for making a diag- 

 nosis, and a highly important date, because if the animal is 

 not pregnant, immediate measures may be taken, such as 

 disinfecting the uterine cavity, preparatory to breeding 

 when the approaching estrum has become established. 



5. The Uterine Arteries 



The uterine arteries afford definite evidences of preg- 

 nancy. As soon as the fertilized ovum has become implanted 



