490 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



Climacteric. — At the sixtieth year the power of producing spermato- 

 zoa, and, therefore, the reproductive power of man, begins to wane. It con- 

 tinues, however, in a diminishing degree, even to extreme old age, and there 

 is no recognized period of ending of the male sexual life. 



In woman, on the other hand, the sexual period continues for only thirty 

 to thirty-five years, and the climacteric, menopause, or change of life, marks a 

 definite ending of the power of reproduction. In temperate climates it occurs 

 usually between the ages of forty-four and forty-seven ; in warmer regions it 

 comes early, in colder late. It is earlier in the laboring classes, and later 

 where menstruation has first appeared early. Its most characteristic feature is 

 the cessation of menstruation, which is a gradual process extending over a 

 period of two or three years and characterized by irregularity in the oncoming 

 and the quantity of the flow, and by gradual diminution. But the cessation 

 of the menses is but one phenomenon in a long series of changes that pro- 

 foundly affect the whole organism and endanger life. The reproductive organs 

 and the breasts diminish in size, and ovulation ceases. The changes in the 

 pelvic organs are in general the reverse of those occurring at puberty. The 

 organic functions generally are rendered irregular; dyspepsia, cardiac palpi- 

 tation, sweating, and vasomotor changes arc frequent; vertigo, neuralgia, 

 rheumatism, and gout are not rare; a tendency to obesity occurs, though 

 sometimes the reverse ; irritability, fear, hysteria, ami melancholia may be 

 present ; the disposition may be temporarily altered ; all of which changes 

 indicate that the female organism at this time sutlers a profound nervous 

 shock. The loss of the weighty function of reproduction and the adaptation 

 to the new order of events are not accomplished quietly. 



Senescence. — The progressive diminution in the power of growth from 

 birth onward throughout life has been mentioned, and may be interpreted as 

 indicating that the process of senescence begins with the beginning of life. 1 

 In the broadest sense this is true, and is confirmed by a study of various 

 organic functions. In the more restricted sense senescence or old age com- 

 prises the period from about fifty years (in woman from the climacteric) 

 onward, during which there is a noticeable progressive waning of the vital 

 [lowers. The leading somatic changes accompanying old age are atrophic and 

 degenerative, but detailed statistics of this period are almost wholly wanting. 

 A marked cellular difference between the young and the old, which is shown 

 by nearly if not quite all tissues, is the relatively large nucleus and small 

 quantity of cytoplasm in the young, the proportions being reversed in the old. 

 This has been pointed out as follows by Hodge" in the nerve-cells of the first 

 cervical spinal ganglion : 



Volume of 

 nucleus. 



Fetus (at birth) 100 per cent. 



Old man (at ninety-two years) 64.2 " 



1 <'/. ( '. s. Minut : Journal of Physiology, 1891, xii. 



2 C. F. Hodge: Anatomischer Anzeiger, 1894, ix.: Journal of Physiology, 1894, xvii. 



