730 SCIENCE PROGRESS 



uterus, i.e. to the uterine mucosa. The experimental examina- 

 tion of this hypothesis was first made by Fraenkel and Cohn (6), 

 who found that the removal of both ovaries from rabbits at 

 various times during the first six days of pregnancy brought 

 about its cessation. Since then a number of observers have 

 conducted similar experiments on various animals, dogs, rats, 

 and guinea-pigs. Although different times were obtained in the 

 separate species, all the results confirm that for rabbits, namely, 

 that if the two ovaries be removed during the first part of 

 pregnancy, it is invariably stopped. Removal of the ovaries at 

 a later stage did not have any effect. 



It is clear, then, that the presence of, at any rate, one ovary 

 is absolutely necessary to the implantation and maintenance of 

 the embryo during the early stages of that process. 



These investigations were pressed still further, and 



Fraenkel (7) tried the result of removing the corpora lutea by 



electric cautery. Control animals were employed in which 



some of the corpora lutea were left untouched. It was found 



that the complete removal of all the corpora lutea from both 



ovaries resulted in the termination of pregnancy if performed 



within the first six days, whereas, so long as some of these 



-structures were left, pregnancy as a general rule pursued its 



normal course. Similar experiments have been repeated by 



'Other workers, and the results fully confirm the previous ones. 



Further evidence of a less direct nature, but also bearing on 

 this point, is forthcoming. It is found that in the rabbit, if 

 •ovulation be provoked by sterile coitus, the formation of corpora 

 ilutea takes place, and simultaneously there occur an enlarge- 

 ment and vascularisation of the uterus. After the thirteenth 

 day repression begins in the uterus, and by this time also the 

 corpus luteum is on the wane. 



The placenta, by means of which the embryo is attached to 

 the uterine wall, is composed of two parts, one of embryonic 

 and one of maternal origin. Loeb (13) found that he could 

 produce deciduomata, the maternal part of the placenta, by 

 making a series of transverse cuts in the uterus, by injecting 

 paraffin wax, and by inserting pieces of glass or platinum. 

 These structures, however, could only be produced from one 

 to ten days after ovulation, that is, only during the time that 

 young, active corpora lutea are present in the ovary, but can 

 be produced during that time even though the discharged ova 



