486 POPULAR SCIENCE MONTHLY 



and greater effort of the heart to drive the blood through them, and 

 in response to this new necessity, the heart becomes enlarged in an 

 effort of the organism to adapt itself to the new unfavorable condition 

 of the circulation established by age. But the power of the heart be- 

 comes inferior along with this hypertrophy or enlargement, and we see 

 that in the old, in order to make up for the feebleness of the enlarged 

 heart, it beats more frequently. In other words, the pulse rate in 

 the old person increases. 3 We find, for instance, that at the time of 



Mean 

 A & e Frequency 



25-30 72 



30-35 70 



35-40 72 



40-45 72 



45-50 72 



50-55 72 



55-60 75 



60-65 73 



65-70 75 



70-75 75 



75-80 72 



80 and over .*.... 79 



birth the pulse rate is at the rate of 134 beats to a minute. It rises 

 slightly during 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 111 ; at five 

 or six years it becomes 98, and at twenty-one years it has sunk to 71 

 or 72. There are thereafter certain minor fluctuations 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 main- 

 tain the necessary circulation of the blood. We see also, as we go 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, which present under the microscope certain clearly 

 recognized 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 



3 My friend, Professor W. T. Porter, has had the kindness to compile the 

 following table for me, showing the pulse frequency from one to eighty years. 

 For the first two months after birth, the rate is about 130, after the third month 

 140. The foetal rate is 135 to 140. 



