The _ovaries_ become shrivelled and fibrotic; the ova disappear or small cysts may form. It is difficult to find statements about the presence or absence of interstitial cells in the senile ovary. Professor Turnbull has kindly informed me that in old women an occasional cell which might be, but is not certainly, an interstitial cell is visible, and that if they are interstitial cells their number must be small and their development poor. The _uterus_ becomes small, its cavity round, and the cervical canal may be obliterated. The _external genitals_ atrophy. The _mamma_ in women shows involution changes and when excessive (cystic disease) these may, as Paul[175] has pointed out, be compared with prostatic enlargement in the male. VII PHYSIOLOGY OF OLD AGE The basis of the physiology of old age is progressive diminution in functional activity, which corresponds to the characteristic structural atrophy of the organs and tissues. Thus the lowered functional activity of its glands is manifest in the dry skin; according to Haneborg[176] there is usually a fall in the percentage of hydrochloric acid in the gastric juice, though Bell[177] disputes this. The lessened amount of mucus from the intestine probably plays some part in the tendency to constipation. Other evidences of lowered metabolic rate are seen in the diminished efficiency of the acid-base equilibrium (MacNider[178]) and the increased degree of urea-nitrogen in the blood, as shown in 50 per cent of 41 persons between 70 and 88 years of age examined by Rappleye.[179] _Temperature._--Before the era of the clinical thermometer it was supposed that the body temperature of the aged was below normal. This belief was part of the ancient view that the cause of old age was exhaustion by the natural heat of the radical moisture which, like lamp oil, supported the innate heat and with the passage of years could not be supplied as perfectly as before; as a result of this loss of radical moisture the body was thought gradually to dry and cool.[180] But it is now known that the internal temperature is almost constant at all ages, and Charcot proved that the only real difference is that the axillary is lower than the rectal reading; this is due to the diminished vascularity of the skin and to the corresponding fall in the loss of heat, which again may be correlated with the lower metabolic rate of old age. Aub and Dubois’[181] observations on six men between 77 and 83 years of age, mainly with arteriosclerosis, granular kidney, and emphysema, showed that the basal metabolism was 12 per cent below the average for men between 20 and 50.