THE HORMONES IN HUMAN REPRODUCTION 



instead of 16, and a first-class embryologist who made a 

 determined effort to work out the estrous cycle of the rat by 

 the best means at his command, came out with a result of 11 

 days, just twice as long as the correct figure, having somehow 

 missed alternate cycles. 



It can be imagined with what enthusiasm those of us who 

 were working in the field learned of the simple discovery 

 announced in 1917 by C. R. Stockard 6f Cornell Medical 

 College and his colleague G. N. Papanicolaou." These men 

 found that in the guinea pig the cyclic changes, which take 

 place in the reproductive tract under the influence of the 

 ovarian hormones, are seen with especial clearness in the 

 lining of the vagina. Here there is a cycle of growth and shed- 

 ding of the surface cells, which follows events in the ovary so 

 closely that the time of rupture of the follicle can be deter- 

 mined within one hour. It is only necessary to scrape the 

 vaginal lining gently with an instrument, or to wash the 

 cavity out with a medicine dropper and a little salt solution, 

 and study the findings under the microscope. This can be done 

 in a few minutes and does not harm or upset the animal in any 

 way. The vaginal closure membrane, mentioned on page 68, 

 as a peculiarity of the guinea pig, is of course kept open by 

 these daily examinations. 



In justice it ought to be added here that something of what 

 Stockard and Papanicolaou found had been described in the 

 1890's in more or less forgotten papers by several investiga- 

 tors, particularly the French observer, Lataste; but it was 

 their masterly and complete investigation of the matter which 

 made it available to science. 



By the use of this method Stockard and Papanicolaou 

 promptly ascertained the correct length of the guinea pig's 

 cycle and secured a much more accurate timing and descrip- 

 tion of the subsequent events of the cycle than we had before. 



5 C. R. Stockard and G. N. Papanicolaou, "Oestrous cycle in the 

 guinea pig," American Journal of Anatomy, vol. 22, I9I7. 



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