258 CHARLES K. STOCKARD AND G. N. PAPANICOLAOU 



with the following results: In one case the next ovulation had 

 already occurred at the twelfth to thirteenth day (by the next 

 o^•ulation is meant the ovulation following the last copulation) 

 in one case at the thirteenth day, in five cases at the thirteenth 

 to fourteenth day, in twelve cases at the fourteenth to fifteenth 

 day, in four cases at the fifteenth to sixteenth day, in one case 

 at the sixteenth to sixteenth day and a half, in one case at the 

 sixteenth to seventeenth day, in one- case after eighteen days, 

 while in eight cases ovulation had not yet occurred at the time 

 when the animals were killed. 



Loeb also cauterized the corpora lutea in the ovaries of thirty- 

 one guinea-pigs but the results, oAving to the inferiority of this 

 method, were not so satisfactory. The ovulation in some cases 

 came at the fourteenth to fifteenth day, in other cases later. 

 Loeb interpreted these experiments to indicate that the removal 

 of the corpus luteum hastened the next ovulation. Such a con- 

 clusion is in no way actually contradicted by our observations, 

 yet the experiments of Loeb are not completely satisfactory in 

 the fight of the present findings Loeb thought the usual 

 sexual period, or time between two ovulations, in the guinea-pig 

 was very much longer, and much more variable than it actually 

 is. On such a basis it seemed that the ovulation period in the 

 animals he examined had been considerably reduced. But as 

 the present study shows the normal oestrous cycle in the guinea- 

 pig is from fifteen to seventeen days, usually about sixteen 

 days with very insignificant variations. So that the periods re- 

 corded by Loeb, after the operations are actually just about of 

 normal duration. He found the greatest number of cases to 

 ovulate after a period of fourteen to fifteen days (12 such cases 

 or 28.57 per cent) and considered this much shorter than the 

 normal condition, where as a matter of fact such a period differs 

 only insignificantly from what we find to be the regular length 

 of the oestrous cycle. 



When we also take into account his method of calculating the 

 days between the last copulation and the next ovulation, and 

 especially the fact that he figured the ovulation time by the 

 condition and probable age of the newly formed corpora lutea 



