274 
curred at the normal term, notwithstanding 
the injections, seemed to us therefore of 
greater significance. Corner and Hurni, how- 
ever, go further in their conclusions and state: 
“Thus it would seem that Loeb’s experiments 
do not prove an acceleration of ovulation fol- 
lowing the removal of the corpora lutea.” 
This conclusion rests (1) on the lack of ef- 
fect of the injection of dried corpus luteum 
substance in inhibiting ovulation. (2) On the 
alleged proof given by Stockard and Papani- 
colaou that I assumed the normal sexual eycle 
in the guinea-pig to be longer than they found 
it to be by a method which they believed to be 
superior to the one which I used. 
Inasmuch as, to my knowledge, my investi- 
gations provide the essential experimental 
basis for the conclusion that the corpus luteum 
has the stated function, and that the denial of 
the correctness of my conclusion would invali- 
date the significance of the corpus luteum as 
an important factor in the mechanism regu- 
lating the sexual cycle, I believe it advisable to 
inquire whether or not the statement made by 
Corner and Hurni is warranted by facts. 
Without going into a detailed restatement 
of the results which I have published in a 
series of preceding papers, I may give a brief 
summary of some of the essential results ob- 
tained. In a first series of investigations I de- 
termined the duration of the sexual cycle in 
guinea-pigs in which in most cases the uterus 
had been subjected to certain experimental 
interferences in the early period of the sexual 
eycle.® It was found that while in these cases 
the second ovulation may occur as early as 
16-18 days after the first ovulation, it oc- 
curred quite commonly somewhere between the 
twentieth and thirtieth day after ovulation; 
this was found to be so, especially in cases in 
which through incisions made into the uterus 
deciduomata had been produced experiment- 
ally. In a series of guinea-pigs in which the 
uterus had been treated in a way similar to the 
control series, but in: which, in addition, at an 
6 Leo Loeb, Deutsch. mediz. Wochen., 1911, No. 
1. Zentralblatt f. Physiol., 1910, XXIV., No. 6; 
1911, XXV., No. 9. 
SCIENCE 
[N. 8S. Vou. XLVIII. No. 1237 
early stage of the sexual cycle the corpora 
lutea had been completely extirpated with a 
knife, ovulation occurred in the large ma- 
jority of cases between the twelfth and 
sixteenth day after the first ovulation. A 
period of approximately 9 to 13 days fol- 
lowing an ovulation is required for the new 
formation of mature follicles in the guinea- 
pig, each ovulation in the guinea-pig being ac- 
companied by an atresia of all but the smallest 
follicles.7| While this series, as such, proved 
the significance of the corpus luteum for the 
duration of the sexual cycle, the correctness of 
our interpretation was made certain by our 
further finding that while in the normal course 
of pregnancy ovulation does not occur in the 
guinea-pig, after a preceding extirpation of 
the corpora lutea about 6—7 days following 
copulation the pregnancy may proceed, but an 
early ovulation occurs, notwithstanding the 
presence of pregnancy just as it does after ex- 
tirpation of the corpora lutea in the cycle un- 
accompanied by pregnancy. In this case the 
difference in the time of ovulation is so great 
as the result of the extirpation of the corpora 
lutea that an error of interpretation can be ex- 
cluded with certainty. 
Extirpation of the corpora lutea did not 
exert this effect on the sexual cycle in a purely 
mechanical way; excision of control pieces of 
ovarian tissue did not have the typical effect; 
neither did such cases respond in which the 
extirpation of the corpora lutea was incom- 
plete. Complete extirpation of corpora lutea 
on the other hand exerted its effect on both 
ovaries, even in cases in which one of the two 
ovaries had been free from corpora lutea at the 
time of extirpation. It was probable that this 
inhibiting effect of the corpus luteum was due 
to the secretion of a substance on the part of 
the corpus luteum. 
In further experiments I showed that the 
presence of the corpus luteum did not inhibit 
the maturation of follicles, but merely the rup- 
ture of mature follicles. ‘ 
In my first publication I called attention to 
the possibility that the experimental interfer- 
7Leo Loeb, Journal of Morphology, 1911, 
XXIL., p. 37. Virchow’s Archiv, 1911, CCVI., 278. 
