INTERNAL SECRETION OF CORPUS LUTEUM 193 



development in pregnancy to a uterine myometrial gland. 

 Hammond (264), however, was unable to find such a gland with 

 any regularity. The evidence that no foetal factor is required 

 for the complete development of the glands has always been 

 strong and has recently become conclusive. In the egg-laying 

 mammals where no intra-uterine development of the embryo 

 takes place and where, therefore, no foetal hormone can function, 

 the mammary glands proceed to their full development and 

 function normally. Loeb and Hesselberg (403) found no mam- 

 mary development in the rare cases where pregnancy persisted 

 for some time after removal of the corpora lutea, but, as these 

 authors point out, abortion finally took place before extensive 

 proliferation would have occurred even in normal pregnancy. 

 Hammond (263) has shown that the presence of decidual tissue 

 during pseudo-pregnancy in the rabbit does not increase the 

 mammary development. The real answer to the question, 

 however, is to be found by prolonging pseudo-pregnancy to 

 the length of normal pregnancy. In the rabbit the slighter 

 mammary development during pseudo-pregnancy, as com- 

 pared with that during true pregnancy, might be due to the 

 much shorter duration of the former period. In the ferret, where 

 pseudo-pregnancy has the same duration as true pregnancy, the 

 development of the mammary glands during both periods is 

 identical (267). Loeb (401) was able to prolong the life of the 

 dioestrous corpora lutea in the guinea-pig to the duration of 

 pregnancy by the operation of hysterectomy. In such animals, 

 subjected to prolonged luteal action, the mammary glands 

 underwent development comparable,. if not quite equal, to that 

 found in pregnancy. 



Recently it has been possible to prolong pseudo-pregnancy in 

 the rabbit to the same length as true pregnancy (502). It was 

 thought that this could be done by the continuous injection of 

 the virgin animal with the sodium hydroxide luteinizing pre- 

 parations of the anterior pituitary body. In practice, however, 

 prolonged administration of such crude preparations affected 

 the animal adversely, and it was found preferable to start the 

 injections at the end of pseudo-pregnancy and to prolong the 

 life of the corpora lutea so as to stretch out pseudo-pregnancy to 

 the length of true pregnancy. Under these conditions, in spite 



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