THE CORPUS LUTEUM 731 



be excluded from the uterus. As the uterine growth did not 

 take place in the absence of mechanical stimulation, it appears 

 as if the formation of the maternal part of the placenta is due 

 to two causes : Firstly, the presence of corpora lutea in the 

 ovary conditions the possibility of its formation, and secondly, 

 a mechanical stimulus, supplied normally by the fertilised ovum, 

 calls forth the response. 



The experimental evidence therefore shows that there is an 

 intimate connection between the corpora lutea and the early 

 uterine changes. The nature of this connection will now be 

 discussed. 



During the above inquiry into the production of deciduomata 

 it was noticed that if the corpora lutea were all removed the 

 first day or two after ovulation no response could be obtained. 

 If they were removed six days afterwards the response, 

 although obtained, was not so marked as if the ovaries were 

 left intact, so that the effect of the corpora lutea is cumulative. 

 Again, portions of the uterus transplanted to the sub-cutaneous 

 tissue also produced deciduomata if the transplantation was 

 carried out from five to seven days after ovulation. If when 

 the uterine tissue was transplanted the ovaries were also 

 extirpated, it was found that the response was not nearly so 

 marked as if the transplantation alone had been effected but 

 the ovaries not interfered with. These transplanting experi- 

 ments appear to exclude the possibility of the stimulation being 

 nervous in nature, and the fact that it is cumulative, even when 

 the uterus is removed to another part of the body, suggests 

 that the stimulus is a chemical one carried by the blood. 



To sum up briefly, then : The presence of a corpus luteum 

 is essential to the uterine changes connected with the implanta- 

 tion of the ovum ; and its maintenance during the early stages 

 of pregnancy. Under the influence of the corpus luteum the 

 uterine mucosa becomes so sensitised that it will form the 

 maternal part of the placenta in response to a certain stimulus 

 normally provided by the fertilised ovum, but which may be 

 replaced by a mechanical one. Some evidence is also available to 

 show that the stimulus is a chemical one carried by the blood. 



The Mammary Gland Growth in Early Pregnancy 



The second of the two hypotheses concerns the relation 

 existing between the corpus luteum and the mammary glands. 



