Ovulation 



51 



Physiologically, estrum and ovulation are inhibited by 

 pregnancy ; abnormally, they occur while the animal is preg- 

 nant and the fetus alive and well. 



4. Menstruation 



If a heifer or a cow fails to conceive, when estrum, copu- 

 lation, and ovulation have occurred, or if copulation has 

 failed, she regularly menstruates. If she conceives, she 

 does not as a rule menstruate. Evidently the engorgement 

 of the uterus during estrum is designed to fit the genital 

 tract for the protection and nutrition of the fertilized ovum. 

 Should fertilization fail, capillary hemorrhage from the 

 placental areas follows. The volume of hemorrhage is suf- 

 ficient that the blood is expelled through the vagina and 

 vulva to stain the exterior vulvar region and adjacent parts. 

 Upon the killing floor of the abattoir, heifers or cows having 

 in their ovaries ripe ovisacs have engorged uteri with special 

 engorgement of the placental areas. If the ripe ovisac has 

 ruptured, and presumably fertilization has failed, the pla- 

 cental areas are covered over with thin coagula of bright 

 red blood. Later this is expelled, to constitute the menstrual 

 fluid. The exact significance of menstruation is not fully 

 determined. By my observations I have been led to the con- 

 clusion that menstruation constitutes reliable evidence of a 

 failure to conceive, so far as the estrum just past is con- 

 cerned. Apparently there are exceptions to the rule. 



There is much controversy amongst embryologists and 

 human obstetrists regarding the relationship between men- 

 struation, ovulation, and conception. There is no outstand- 

 ing estrual period in woman, and scant opportunity for the 

 clinical study of ovulation. The cow offers the best available 

 animal for such study. Her estrual period is sharp, clear, 

 and brief; the ovary is conveniently palpated per rectum; 

 the ripe ovisac is clearly recognizable by palpation ; and the 

 crater of the recently ruptured sac is clearly palpable. The 

 order of the phenomena is clearly and indisputably — 

 maturation of the ovisac, estrum (with copulation, if oppor- 

 tunity exists), ovulation, and fertilization, or, if fertilization 



