Senile Changes in Leaves of Certain Plants 285 



Deterioration in rapidity and coordination of movement. — According to 

 Miihlmann (1901) the musculature of man ceases to grow at about the age 

 of thirty-six, but the experience of highly trained athletes indicates a 

 considerably earlier appearance of decrease in muscular power and co- 

 ordination. 



Deterioration in the powers of special sense. — The tendency toward 

 deafness and failing sight are common manifestations of deterioration in 

 the powers of special sense. 



Deterioration in efficiency of excretion. — While the belief that deterio- 

 ration in efficiency of excretion is always present is based partly on 

 theoretical considerations rather than on extensive tests, there can be 

 little doubt of its truth. In dealing with the various theories of senility 

 this function will be again referred to. 



Deterioration in reproductive power. — Decreased reproductive power is 

 more marked in the female than in the male. 



Deterioration in all the internal activities characteristic of living animals. — 

 There can be little question of the presence of a general deterioration in 

 internal activities of animals, even in the central nervous system, but 

 exact investigations are wanting. 



SENILE changes IN THE STRUCTURE OF ANIMAL ORGANS 



The changes discussed below seem to be of a type not appearing in 

 early life. 



Decrease in the size of all organs, due to atrophy of the cells and of the 

 intercellular substance. — Douaud (1867), Kolliker (1897), and others since 

 their times, have investigated the senile atrophy in muscles. Metchnikoff 

 (1908) presents further studies in which he claims that the destruction 

 of the contractile power is produced by a special kind of phagocyte. 

 Senile atrophy of the brain has been investigated in man and in bees by 

 Hodge (1895), who found that the decrease in size was largely due to actual 

 death and disappearance of cells, as well as to shrinkage of the hving 

 cells. In all cases when the organs of animals in the condition of extreme 

 senility have been studied, the appearance of loss and degeneration of 

 cells is presented. The ductless glands — the thyroid, for example — 

 show this degeneration and have been utilized by Lorand in the formu- 

 lation of a theory of senility. 



