vii THE STAGES OF LIFE AND DEATH 295 



Wolff in a dissertation entitled De senectutis natura (1748), 

 after stating that "sanissimus homo senescit," concludes that 

 " oportet ut id in essentia hominis in genere fundatum sit," and 

 proceeding to analyse the principal cause of old age, attributes it 

 to the " resistentia fibraruni . . . magis magisque increscens," 

 which, becoming more marked in the vascular system, leads to 

 death from cardiac disorders. 



Eichter (1724), a disciple of Vater, influenced by the new 

 study of the glandular organs, found the cause of old age in the 

 influence of the secretions upon the exchange of material, which 

 he regarded as bound up with the " imuiinuta reparatio absumpti." 

 This view has been adopted in recent times by Lorand (1904), 

 who sees in old age merely the action of the endocrine glands, 

 which he thinks preside over and regulate the trophic processes 

 of the organism. In premature senility he finds analogies with 

 myxoedema. 



Erasmus Darwin agreed with the medical authorities of his 

 day in the view set forth in his Zoonomia, that old age depends 

 upon the " exhaustion of irritability." "It seems," he writes, " our 

 bodies by long habit cease to obey the stimulus of the aliment 

 which should support us. After we have acquired our height 

 and solidity we make no more new parts, and the system obeys 

 the irritations, sensations, volitions, and associations, with less 

 and less energy, till the whole sinks into inaction." 



Valli tried to find in chemical phenomena an explanation of the 

 organic changes of old age, which he ascribed to the accumulation 

 of calcium phosphate in the interior of the tissues, hardening and 

 solidifying them and impeding or stopping their action. Hamelin, 

 on the other hand, connects old age with the natural process of 

 ossification which begins during foetal life and ends with death. 



Other writers have limited the state of senile involution to 

 a given tissue or organ, for instance to the respiratory system, 

 with consequent imperfect formation of blood (Keveille') or con- 

 tinuous production of connective tissue (Boy-Tessiers). Others 

 again regard old age as resulting from a chronic intoxication 

 (Brousse), or from progressive arteriosclerosis (Charcot). This 

 last view merits special attention. 



Arteriosclerosis is regarded by some not as a morbid process 

 in the ordinary sense of the word but as a physiological process, 

 one of the necessary heritages of human evolution, easily identified 

 with the process of senility. They adduce various arguments in 

 favour of this identity of arteriosclerosis and old age : 



1. In old age the tissues of the organism are subject to gradual 

 fibrous and sclerotic metamorphosis. 



2. Senility is hastened by the same causes which induce morbid 

 arteriosclerosis, and especially by excessive muscular work, grief, 

 and the abuse of alcohol 



