INTERNAL SECRETION OF CORPUS LUTEUM 175 



these occurrences in the accessory organs is not precisely known, 

 but the anterior pituitary body is presumably concerned (see 

 p. 171) . Having been stimulated, the corpus luteum elaborates 

 the internal secretion which performs its various functions. 



Many experiments have been carried out on the experimental 

 ablation and stimulation of the corpora lutea, and as a result of 

 these it is possible to state that four functions are performed by 

 the corpora lutea of pregnancy, pseudo-pregnancy, or lactation. 

 These functions may be summarized as follows: 



(a) The inhibition of ovulation and of oestrous changes in the 



accessory organs. 

 {b) The sensitization of the uterus for the implantation of 



fertilized ova. 



(c) The development of the mammary glands from the 



condition in which they are found at oestrus to that 

 characteristic of the end of the luteal phase. 



(d) The maintenance of pregnancy. 



Methods of removing the corpora lutea. Experimental work on 

 the functions of the corpora lutea has dealt mainly with the 

 effects of their removal. The exact methods by which this has 

 been achieved have varied considerably and some importance 

 attaches to this point. Most workers have performed double 

 ovariectomy in order to remove the corpora lutea, but this 

 method has the great disadvantage that all ovarian activity is 

 eliminated; it is therefore quite useless in work dealing with 

 the return of oestrus. In large monotocous animals, such as the 

 cow, the corpora lutea can readily be squeezed out from the rest 

 of the ovary, but in smaller animals, such as the rabbit, 

 surgical dissection or cauterization has to be employed if the 

 corpora lutea only are to be eliminated. Such an operation is 

 very severe and may easily lead to post-operative effects which 

 may be confused with those due to ablation of the corpora lutea. 

 As regards the operation during pregnancy, for instance, several 

 workers have found that their control experiments (cutting the 

 ovary, etc.) gave almost the same results. In an animal as small 

 as the mouse even these methods are impracticable. The ideal 

 subject for experiments of this nature would be a small mono- 

 tocous animal in which the ovary containing the corpus luteum 



