284 



Harris M. Bexedict 



A curve graphically representing the change in pulse rate has been plotted 

 and is shown in figure 52. Here again there is seen a more rapid decrease 

 in earlj^ life than later. It is evident that the rates of growth, of res- 

 piration, and of heartbeat are but the most obvious indicators of the 

 degree of metaboUc activity of the animal protoplasm. 



The increase in rate of respiration and of heartbeat that occurs in the 

 last years of life is an example of a struggle between the depressing force 

 of seniUty and the accelerating stmiuh exerted on the lungs and the heart 

 by the other organs of the body. The organs composing the body of an 

 animal are so interrelated that a need in one produces a stimulus to action 

 in any organ which can satisfy that need. In the last years of life the 



organs supphed with oxygen and 

 relieved of harmful waste products 

 by the faihng lungs and heart, 

 reach such a conchtion that the re- 

 sulting stimuK become so powerful 

 as to more than neutralize for a 

 time the effects of senihtj^ in slow- 

 ing the beat. 



This power of one part of the 

 body to stimulate another organ 

 leads to many cases of apparent 

 suppression of the effects of senil- 

 ity, especially in the stages of youth 

 and maturity of the animal body. 

 Contrary to the usual custom, these 

 have been placed in a group l^y themselves as those evidences of senihtj^ 

 that become visible only at some stage later than that of youth. These 

 activities are spurred on by the stimuh resulting from then- interaction 

 with the other activities of the body. For example, the mcrease of mus- 

 cular strength and coordination due to the interaction of the muscular and 

 nervous systems, which characterizes the first third of human fife, is 

 made possible. 



Deterioration appearing later in life 

 The first four types of deterioration given as appearing later in life 

 deal with activities in contact with the external world, and are therefore 

 the most obvious. 



120 



SO 



S 40. 



10 



20 



Fig. 52.- 



30 40 50 60 70 

 Age in j'ears 



-Curve of senile decrease in rate of 

 heartbeat of man 



