ORGANS OF INTERNAL SECRETION 341 



not take place until oestrus, and consequently that at the 

 time of the procestrous hyperaemia there are no corpora lutea 

 present in the ovary. These facts, however, are in no way 

 opposed to that part of Fraenkel's theory which assigns to the 

 corpus luteum the function of governing the fixation of the 

 ovum and helping to maintain its nutrition during the first 

 stages of pregnancy. 



Dr. Jolly and the author ^ have carried out a series of experi- 

 ments upon dogs and rats in which the ovaries were extir- 

 pated at different stages during pregnancy, as in Fraenkel's 

 experiments upon rabbits. In the experiments on dogs, 

 ovariotomy was performed at intervals ranging from three days 

 to four weeks after impregnation. The pregnancy was dis- 

 continued in every case excepting one, in which a portion of the 

 right ovary which contained the degenerate remains of two 

 undoubted corpora lutea were found post mortem, three days 

 after parturition, when the dog was killed. In this experiment 

 ovariotomy was performed three days after copulation, and 

 parturition occurred fifty days subsequently. Only a single 

 pup was produced, and birth was premature. The pup died 

 after being suckled normally for three days. The ovaries were 

 also removed from a large number of rats, most of which were in 

 early stages of pregnancy. Pregnancy was continued in no 

 case in which ovariotomy was performed during the first six 

 days. In other cases, in which the ovaries were removed at 

 periods varying from the sixth day until near the end of 

 pregnancy, the young were produced normally at full time.^ 

 Control experiments were also carried out in which the ab- 

 dominal cavity was opened up during an early stage of pregnancy 

 and the ovaries were cauterised, or in which one ovary was re- 

 moved and not the other, and in these experiments the course 

 of pregnancy was not interfered with.^ We purposely refrained 

 from attempting to extirpate the corpora lutea only while 

 leaving the rest of the ovary, as it appeared to us to be 

 practically impossible to destroy the whole of the luteal tissue 



' Marshall and Jolly, loc. cit. 



' In our paper the period of gestation in the rat was wrongly computed 

 at twenty-eight days. It is in reality about twenty-one days. 

 ' Gf. Carmichael and Marshall, loc. cit. 



