THE INSTINCT OF SURVIVAL 119 



pair its workings, the human machinery is at last 

 subjected to a multiplicity of degenerative tend- 

 encies, which, having usually had their quiet incep- 

 tion in middle life, now begin to obtrude themselves 

 by giving origin to one or more disorders of function 

 which result in symptoms of diminished capacity 

 for work. The occasional disorder, the warning 

 weakness, has given place to the permanent, the 

 chronic enfeeblement. The chronic degeneration of 

 the heart muscle, the fibrous and fatty and calcareous 

 change in the blood vessels, the shrunken kidney, 

 denuded in part of its degenerated epithelial cells, 

 the established wasting of the working epithelial 

 cells of the stomach and intestine, the impoverished 

 blood, these are some of the common results of 

 the gradual physiological wearing out of the living 

 tissues, and they are further aided and hastened by 

 the acute bacterial infections, with which the or- 

 ganism has almost inevitably had to reckon from 

 time to time. It is not surprising that these changes 

 in the living protoplasm of the cells should entail 

 a weakening of the defenses of the body as a whole, 

 and that in consequence of this the period of senility 

 should be one beset with the varied dangers of in- 

 fection. Old age is, in fact, a period of susceptibility 

 to almost every kind of bacterial danger, including 

 gastric and intestinal infections, bronchitis, pneu- 

 monia, influenza, tuberculosis, and bacterial invasions 

 of the kidney, bladder, and genital tract. Death 

 may, indeed, come acutely with a final bacterial 



