676 THE PHYSIOLOGY OF REPRODUCTION 



two beats per minute rising to seventy-nine or eighty. The 

 rate of respiration also rises slightly, and the vital capacity of the 

 lungs diminishes. Moreover, the amount of carbon dioxide and 

 urine which are excreted becomes less. The pigment in the 

 hair undergoes absorption, the hair turning grey or white. The 

 adipose tissue beneath the skin disappears, especially in ad- 

 vanced old age, but fatty degeneration of muscle or glandular 

 tissue is not infrequent. In the male sex the prostate gland 

 undergoes atrophy, or in some cases a pathological hypertrophy, 

 which is said to be the cause of frequent penile erections. 



It has been shown also that the brain decreases in size in 

 old age. The shrinkage begins soon after maturity, and then 

 continues almost steadily to the very end of life.^ Handmann ^ 

 has published the following statistical results, which are based 

 on measurements carried out at the Pathological Institute at 

 Leipzig : — 



Weight of Brain. 



Age. Male. Female. 



4-6 .... 1215 grams. 1194 grams. 



7-14 .... 1376 „ 1229 „ 



15-49 .... 1372 „ 1249 „ 



50-84 .... 1332 „ 1196 „ 



The decrease in brain weight is accompanied by a diminution 

 in the thickness of the cortex and in the number of tangential 

 fibres present in it. These changes are associated on the 

 psychical side with a gradual mental failure — loss of memory, 

 decrease in the power of original thought and in the assimilation 

 of new ideas, and general decline of mental activity. Moreover, 

 the reaction time is lengthened, the sense organs lose their 

 delicacy, and in the eye the power of accommodation is largely 

 lost. 



The minute cellular changes in the tissues are no less pro- 

 nounced. These also are in the direction of atrophy. There 

 is a general shrinkage in the protoplasm of the cells, but especially 

 in the nuclei, so that the relative amount of cytoplasmic to 

 nuclear substance becomes increased in old age. The nucleoli 



' Minot, loc. cit. 



' Handmann, " tjber das Hirngewicht des Mensohen," Arch. f. Anat. u. 

 Phys., anat., Abth., 1906. 



