THE CORPUS LUTEUM 735 



As in the case of the uterine changes, so also here the 

 experimental evidence points strongly to a connection between 

 the corpora lutea and mammary gland growth. Again also the 

 facts indicate that the connection is a chemical one. 



The nerves supplying the mammary gland in the goat were 

 cut without interfering with the growth of the gland during 

 pregnancy or consequent lactation. In ,the dog the spinal cord 

 was severed above the point of origin of the ovarian nerves, and 

 a similar lesion resulting from an accident is also recorded in a 

 woman, and in neither case were the growth and activity of the 

 mammary gland interfered with. These seem to exclude the 

 possibility of any nervous stimulation. In the guinea-pig, 

 however, single mammary glands have been transplanted to 

 the subcutaneous tissue behind the ear without the growth 

 during pregnancy being interfered with, so that the stimulus- 

 in these cases must have been a chemical one carried by the 

 blood. 



The use of the term hormone has been carefully avoided 

 because as yet no definite evidence has been adduced to show 

 that the corpora lutea produce a specific secretion which when 

 poured into the blood stream directly influences the mammary 

 glands. As has been indicated above, the presumptive evidence 

 is strongly in favour of such a direct chemical stimulus, but the 

 experiments of injecting corpus luteum extract that have been 

 tried up to the present have yielded only negative results. This 

 failure, however, may simply be because the technique was at 

 fault. 



It has been attempted in the foregoing to set out the evidence 

 now available to show that the corpus luteum is a well-marked,, 

 glandular body with a very definite and characteristic histological 

 structure that periodically forms and disappears in the mamma- 

 lian ovary — that it secretes a substance of lipoid nature. 

 While present in the ovary corpora lutea may retard subsequent 

 ovulation. Its principal work appears to be that by means of a 

 chemical stimulus acting directly or indirectly it controls the 

 uterine changes necessary for the attachment of the embryo in 

 the early stages of pregnancy and also incites the formative 

 growth of the mammary glands during the same and at other 

 times. 



The corpus luteum, then, is a gland that is present in a well- 

 developed condition in the three sub-classes of the Mammalia,, 



