vii THE STAGES OF LIFE AND DEATH 291 



Although man's mental powers suffer less from the passing of 

 the years than does his muscular strength and frequently remain 

 unimpaired when his body has ceased to be capable of the lightest 

 manual labour, history shows that men of science have made most 

 of their great discoveries and written their most important works, 

 which form the patrimony of our civilisation, during the period 

 of virility, between their fortieth and their sixtieth year; for 

 this statement we have the witness of history. Amongst such 

 works are Galileo's Nuncius sidereus ; Linnaeus' Species plan- 

 tarum ; Newton's Principia ; Descartes' Discours de la me'thode ; 

 Kant's Kritik der reinen Vernunft ; Lamarck's Philosophic zoolo- 

 gique ; Mueller's Physiologic des Menschen ; and Darwin's Origin 

 of Species. 



The long period of maturity or virility, the most important 

 and the longest in life, is usually subdivided into three stages : 



(a) Increasing virility, termed by Sallust and Cicero juventus, 

 during which the constitution and physical powers are being 

 brought to perfection; it comes to an end between thirty and 

 thirty-five years of age in women, but lasts until forty in men. 



(&) Stationary virility, termed aetas constans by the ancients, 

 during which the organism and powers remain unchanged ; it lasts 

 from the thirty-fifth to the fortieth year in women and from the 

 fortieth to the fiftieth in men. 



(c) Decreasing virility, from the fortieth to fiftieth year in 

 women and the fiftieth to the sixtieth in men. 



In the case of women the end of maturity coincides with the 

 end of fecundity the cessation of menstruation. Though this is 

 the most noticeable symptom of this stage, it is by no means 

 the most important, since it is accompanied by great changes 

 in the organism. In all languages we find popular expressions for 

 the organic disturbances, the dangers and inconveniences connected 

 with the end of sexual life (critical age, climacteric, etc.). We 

 have dealt at length with these disturbances in the preceding 

 chapter. The order in which these morphological and physio- 

 logical phenomena of the menopause take place varies in different 

 women. Hegar, when treating of the changes undergone by the 

 genital organs, considers that atrophy of the ovary precedes that 

 of the uterus, and adduces as an argument for this theory the fact 

 that fecundity diminishes gradually before menstruation ceases. 

 Lawson Tait, on the contrary, is of the opinion that ovulation may 

 last long after this cessation, and thus admits the possibility of 

 conception during the change of life. Ovaries normal in size and 

 structure have been found several years after the menopause (Peuch, 

 Mangiagalli), a proof that the cessation of menstruation is no in- 

 dication that the atrophy of the ovaries, as far as their essential 

 characteristics are concerned, has reached its extreme limits. 



Various physiological factors, such as race, heredity, sexual 



