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A TEXTBOOK OF PHYSIOLOGY 



isolated from testicular extracts, may be used to increase neuro- 

 muscular activity and lessen fatigue, and thus be of service in old 

 age, when the testes are failing to act. Some advertised patent 

 medicines on the market claim on untrustworthy evidence to give 

 wonderful rejuvenating effects. They contain a certain amount of 

 extract of boar's testicles. 



Whether the general effect of excision or transplantation upon 

 metabolism be so great as is supposed by some, it is obvious that 

 upon the growing animal the effects are far-reaching. For instance, 

 in man, not only are the secondary male characteristics called forth 

 e.g., the beard, the large larynx, etc. but the growth of the skeleton 

 is affected, so that it is possible to differentiate between the male 

 and female skeleton. It is probable that such secretions may !><' 

 held partly responsible for the different outlook of man and of 



FIG. 239. HERDWICK RAN 

 (NORMAL). 



The effect of castration on horn-growth is well seen. 



FIG. 2-1-0. HERDWICK WETHER 

 WITHOUT HORNS VISIBLE. 



(Marshall.) 



woman upon life, the cerebral processes differing according as the 

 nervous system is bathed with testicular internal secretion or with 

 ovarian internal secretion. 



The Prostate Gland. It is believed by some that an internal 

 secretion of the prostate gland has an important action on the forma- 

 tion and ejaculation of spermatozoa. There is, however, little evidence 

 for this view. It is generally believed that the prostatic secretion 

 aids the movements of the spermatozoa. 



The Ovary. The interstitial cells of the ovary play much the 

 same part in the female as the interstitial testicular cells in the male. 

 Extirpation of both ovaries in young girls prevents the onset of men- 

 struation, and brings about notable alterations in their appearance. 

 When the ovaries are removed after puberty, menstruation ceases 

 and pregnancy is prevented. There follow some atrophy of the 

 breasts, uterus, and vagina, and a tendency to obesity. 



That these effects are not nervous in origin, as was once believed, 

 is shown by the fact that transplantation of the ovary induces once 



