DEVELOPMENT 455 



must play an important part, for it extends even to the chemism of the 

 nutritive processes. 



Next to nutritional defects those of the circulation are undoubtedly 

 most characteristic of old-age, and are perhaps even more frequently 

 the cause of death. The most important perhaps of these changes is 

 the sclerosis or hardening of the arteries. In old age this is physiological 

 rather than pathological, and is always present in some degree after fifty. 

 It consists of an atheromatous condition of the arterial wall, especially 

 in the larger tubes. Sometimes the change is fibrous, but much oftener 

 calcareous, the essential elasticity of the arteries being in either case 

 diminished or almost lost. This makes it necessary that the heart should 

 work harder to keep up the activity of the capillary-circulation, and it 

 therefore becomes enlarged. Often the heart-walls too are affected in 

 like manner. If a large brittle arteriole burst in the brain, there is 

 apoplexy and resulting death sooner or later; if the heart gives way or fails 

 to meet the demands put upon it, there is likewise death, either at once 

 or after weeks of dropsy, dyspnea, etc. Minor degrees of these conditions 

 are essentially normal after old age has begun, but that they would be 

 so common did not people so often over-use alcohol, dissipate, under- 

 exercise, and eat too much, no man at present can be sure. It remains 

 to be learned through statistics whether lactic acid (found in butter- 

 milk) if taken continually would prevent or lessen this arterial sclerosis 

 so frequent among people more than fifty years of age. 



The pulse-rate is increased in old-age five or ten beats, this increase 

 being necessary, as well as the heart's hypertrophy, to compensate for 

 the inelasticity of the arteries. 



Body-temperature. In old age the temperature is slightly higher 

 on the average than in middle-age, and nearly equals that of infancy. 

 This is brought about, despite the lessened metabolism of advanced 

 age, by the decrease of vaso-motor power. The peripheral vessels are 

 relatively more rigid and smaller than in middle life and so lose less heat 

 from the blood within them by radiation; and less sweat is produced. 

 Despite their rise of temperature, old persons usually feel chilly unless 

 their environment be warm, and frequently when in good health, even in 

 high temperatures. 



Respiration declines in old-age largely because of the defects in the 

 circulation, but also because of the hardening which the costal cartilages 

 undergo, and also from the weakening of the intercostal muscles. Ex- 

 piration especially becomes more difficult because these cartilages are less 

 elastic. This is one reason why broncho-pneumonia is so common and 

 fatal in old persons : the difficulty of coughing and expectoration allow 

 the irritating mucus, bacteria, and other substances to collect in the lungs. 



By the lessening of the respiration the great oxidative process of the 

 tissues is decreased. This is one condition of the smaller metabolism so 

 general in old-age : the fuel is lessened and the vital fire burns ever more 

 dimly out. 



The muscular activity in old-age is greatly diminished. The bones 



