OLD AGE AND DEATH 87 



earlier stages. The muscular layers of the intestinal 

 walls are thinned, and this lessens their peristaltic action. 

 The lungs become stiffened ; the walls between the air- 

 spaces become thick and hard, and the air-capacity of 

 the lungs becomes diminished. The heart is usually 

 enlarged, but its power is impaired, and the pulse-rate 

 is thereby increased. We see also that the germ-cells 

 cease their activity in the very old, and so one of the 

 great functions of life is blotted out entirely from the 

 history of the individual. 



The whole of the nervous system suffers, and, the 

 brain itself shows us without a doubt that after maturity 

 is reached, the shrinkage of the brain begins, and con- 

 tinues steadily to the very end of life. 



Physiology also shows us that the shuffling gait, the 

 tardy response, the slow speech, the imperfect sight, 

 and the difficult hearing, are but signs of lessened power 

 in the muscles, of diminished control over the action 

 of these muscles, of inferior co-ordination, and of nerve 

 decay. 



These are a very few of the features that mark old 

 age among the higher forms, but when we consider 

 many of the lower forms in which few, or it may be 

 none, of the organs and structure mentioned above 

 exist, we are at a loss to find any sign of old age, but 

 still we are met with the fact that they also spring into 

 being, grow old, and die. 



Any theory of old age, the natural corollary of which 

 seems to be death, must explain not only the causes 

 of old age and death in the higher forms, but also in the 



