16 INTERNAL SECRETION 



paratively harmless urea. This is an example of what Biedl 

 calls " negative internal secretion." Since the process is a stage 

 in the elimination of waste material, it might be called " internal 

 excretion " (vide supra, p. 38). 



INrently discovered and extremely interesting examples 

 of internal secretion are furnished by the mechanisms of pan- 

 creatic and gastric secretions (vide infra, pp. 59 and 65). 



There is considerable reason for ascribing an internally 

 secreting function to the testis and to the ovary (vide infra, 

 pp. 66 and 75). Though these are not glands in the usual 

 acceptation of the term, yet many of their constituent cells 

 are of the "glandular," "secretory" type. 



Lane-Clay pon and Starling reported that injections of 

 extract of foetus into a virgin rabbit causes growth of the 

 mammary glands. Starling suggested the name " Hormone " 

 (from 6p pa to = I excite or arouse) for these various substances 

 which act as chemical messengers, and the name has in recent 

 years become generally adopted. Foa finds that injection of 

 extract of foetal calf causes some mammary growth in rabbits. 

 It is concluded, therefore, that the effects described by Lane- 

 Claypon and Starling are not specific for only one kind of 

 animal. 



Heape points out that it is well known that virgin animals 

 sometimes produce milk. So that it seems clear that the 

 beginning of the development of the gland dates from some 

 point of time prior to or during pro-oestrum or oestrus, and 

 occurs normally quite apart from pregnancy, and that since 

 the full functional development of the gland may be experienced 

 by virgin animals, this must occur without any stimulus from 

 a foetus. Heape believes that the source of the stimulus which 

 excites the development of the mammary glands is to be found 

 in what he calls " gonadin," secreted by the ovary at that 

 time, if not in the "generative ferment," which, he holds, 

 governs the activity of the generative glands. 



There is now some considerable evidence that the stimulus 

 to growth of the mammary gland arises from the corpus 

 luteum. This will be referred to again and more fully under 

 the head of " The Internal Secretion of the Ovary and the 

 Corpus Luteum " (vide infra, Chapter IX., Sect. C., p. 75). 



Arguing from the mammary gland experiments, and from 

 those upon the mechanism of pancreatic secretion (vide infra, 



