446 BIOLOGY: GENERAL AND MEDICAL 



discovery of an extremely aged person in whose dead 

 body the supposedly characteristic changes are absent. 

 Two savants have devoted particular attention to the 

 phenomena of senescence. Charles Sedgwick Minot 

 refers all of the senile changes to cellular transformations 

 which he calls " cytomorphosis." His views are sum- 

 marized in the following four laws: 



1. Rejuvenation depends on the increase of the nuclei. 



2. Senescence depends on the increase of the proto- 

 plasm and on the differentiation of the cells. 



3. The rate of growth depends on the degree of 

 senescence. 



4. Senescence is at its maximum in the very young 

 stages, and the rate of senescence diminishes with age. 

 According to Minot, the completion of embryonal de- 

 velopment begins the period of senescence which pro- 

 gresses rapidly as the individual grows into an adult, 

 and more slowly thereafter. 



Elie Metchnikoff refers the senile changes to the in- 

 creasing activity of phagocytic cells by which the less 

 active somatic cells are slowly destroyed. 



There seems to be truth in both doctrines. The 

 more completely the cells are differentiated and special- 

 ized, the less independent and less vital they become and 

 the more readily they fall into decay. 



Let us now examine the human body to determine 

 what may be regarded as the usual signs of old age and 

 in what manner they contribute to final dissolution 

 and death. Be it understood, however, that the order 

 in which the recognized conditions are considered is not 

 by any means the necessary order of their occurrence. 

 Indeed it seems impossible to determine the exact chro- 

 nology of the changes as almost any of the important dis- 

 turbances may establish a " vicious circle" by which it 

 may become intensified, as well as other retrogressive 

 changes inaugurated. 



With increasing age we find atrophic changes in all the 

 organs and tissues of the body. This atrophy is gener- 



