1 6 AGE, GROWTH, AND DEATH 



the first three months of infancy until at the end of 

 the third month it reaches some 140 beats a minute; 

 it soon falls off, however, and at the end of the first 

 year it has sunk to 1 1 1 ; at five or six years it be- 

 comes 98, and at twenty-one years it has sunk to 7 1 

 or 72. There are thereafter certain minor fluctua- 

 tions in the rate of the heart-beat with advancing 

 age, but generally it may be said that this value of 

 72 beats a minute is characteristic of adult life. But 

 when a person becomes eighty years old, it has been 

 found that upon the average the rate of the heart- 

 beat rises and becomes 79 a minute. Hence it is 

 clear that though the heart is larger, it has to make a 

 greater effort, that is to say a more frequent beat, in 

 order to maintain the necessary circulation of the 

 blood. 



Another illustration. We can demonstrate by 

 going back to the anatomical examination of the 

 body, that those important structures which we call 

 the germ cells, upon which the propagation of the 

 race depends, and which present under the microscope 

 certain clearly recognised characteristics by which 

 they can be distinguished from all other cells of the 

 body, that these germ cells cease their activity alto- 

 gether in the very old, and one of the great functions 

 of life is thus blotted out altogether from the history 

 of the individual. 



Turning now to the yet nobler organs, especially 

 the brain, we see a curious change going on, a change 

 of which old age presents to us the culminating re- 



