DIOESTROUS CYCLE IN THE GUINEA-PIG 257 



During pregnancy in higher forms, according to Beard's 

 scheme the corpus luteum exerts a protective function by pre- 

 venting a new ovulation and an abortive birth. In non-preg- 

 nant females, however, this abortive process is not counteracted 

 by the quickly degenerating corpus luteum spurium and the 

 uterus undez'goes the changes of menstruation and a new ovula- 

 tion occurs. This ingenuous theory aims to furnish an expla- 

 nation of the periodically destructive changes occurring in the 

 uterus and vagina of some mammals at the same time that the 

 ovary is preparing to liberate its ova. And the chief virtue 

 of the theory is that it points out the protective action of the 

 ovary and especially of the corpora lutea on the uterine mucosa. 

 Every menstruation process and every abortion reflex as well as 

 every normal birth is the result of two different factors, one the 

 condition produced by the absence of the luteal secretion and the 

 other is the expression of a phylogenenetically and physiologi- 

 cally fixed rhythmical tendency within the uterus itself. 



Beard's conception of the corpus luteum as an organ preventing 

 ovulation has been adopted and further developed by many 

 later investigators, Prenant, Sandes and Skrobansky, Leo Loeb, 

 Ruge, Pearl and Surface, Halban and Kohler and others. All 

 of these investigators have a,dded evidence in favor of Beard's 

 corpus luteum theory partly by new observations and partly by 

 experiments on the living animals. 



To state Beard's ('98, p. 101) position in his own words: 



The corpus luteum is probably a contrivance for the supression or 

 rendering abortive of ovulation during gestation. The commencing 

 degeneration of this structure some little time before the end of the 

 gestation (like its rapid atrophy where fertilization has not taken 

 place) allows of preparation being made for a new ovulation. 



We are indebted to Leo Loeb ('11), for first putting these 

 conceptions of Beard to experimental test. And Loeb showed 

 that pregnancy as such does not prevent ovulation if corpora 

 lutea are extirpated from the ovaries. Loeb also destroyed the 

 corpora lutea in non-pregnant guinea-pigs and later examined 

 the ovaries after different periods of time. In forty-two females 

 the corpora lutea were destroyed by cutting them out completely 



