520 Dr. J. E. Lane-Claypon and Prof. E. H. Starling. [Feb. 12 r 



glands, with, in some cases, actual secretion of milk. He would regard this- 

 condition as being a continuance of the state of pro-oestrus leading to- 

 continued growth of mucous membrane and also of the mammary gland. 

 When the impregnation was no longer possible, with the discharge of the 

 ovum, the secretion of this substance ceased, and the absence of the inhibitory 

 stimulus caused break-down of the uterine mucous membrane as well as 

 dissimilative activity of the mammary gland. 



During sexual life, therefore, the ovaries are continually producing a 

 substance which exerts an influence on both glands and uterus. With the 

 occurrence of conception there is at once a great growth of what we may 

 call germinal material. With the growth of the fertilised ovum the amount 

 of hormone produced in the ovum must also increase in proportion. In 

 the early stages of pregnancy the chief source of this hormone may perhaps- 

 be located in the chorionic villi, but with the growth of the body of the 

 foetus this latter must take a preponderating share in the preparation of 

 the hormone. We have no reason to suppose that the foetal elements of 

 the placenta entirely lose this function of the germinal cells, but the negative 

 results of injection of placentas in our experiments show that it is impossible 

 to ascribe to the placenta, as is done by Halban, a preponderating part in 

 the preparation of this hormone. 



If the hormone is produced in the body of the foetus, it might be objected 

 that the formation should goon afterbirth, and therefore lead in the new- 

 born animal to a continuance of the growth both of the mammary gland and 

 of uterus. The profound changes in the environment of the new animal 

 which occur at birth must, however, induce equally profound changes in its 

 metabolism, and there is no difficulty in imagining that with the assumption of 

 extra-uterine life the formation of this substance in the foetus comes to an end.* 



The occurrence of growth in the mammary gland of a virgin rabbit and of 



secretion in the mammary gland of a multiparous rabbit from the injection 



of boiled extracts of foetus, seems to indicate that the specific hormone, like 



adrenalin or secretin, is not destroyed by boiling. Further evidence, 



* In the ornithorhynchus pregnancy is associated with the growth of mammary glands, 

 although the embryo in this animal is contained in an egg, and does not enter into any 

 anatomical connection with the uterine wall. Halban points out, however, that the shell 

 of the egg is porous, and that during its stay in the uterine cavity it increases in size, 

 and the contained embryo grows, in consequence of the absorption of nutrient matei'ial 

 from the fluid contained in the uterine cavity. If the embryo is able to absorb nutrient 

 material from the uterine contents, it is equally able to give up to these contents diffusible 

 substances, which may be taken up by the mucous membrane and carried by the circula- 

 tion to the mammary glands. The condition in the ornithorhynchus cannot therefore be 

 regarded as a disproof of the chemical theory which we have adopted throughout this 

 investigation. 



