298 



THE GUIDE TO NATURE 



Why Does the Heart Beat? 



BY R. W. TOWER AND C. F. HERM. 



Why does the heart beat? It is a 

 question not altogether easy to answer. 

 Perhaps there is no adult who has not 

 counted his own or another's pulse and 

 wondered at the regularity of the rhy- 

 thm with which the phenomenon pro- 



Series of ni^lc li Tit niu cle cell ^^llKll hive been 

 observed to giow bent sepantely unite with one 

 another, and finally beat in unison. 



ceeds. Doubtless every one who has 

 dressed his own catch after a success- 

 ful fishing trip has observed how the 

 heart of the animal beats for some time 

 after it has been removed from the 

 body, and has asked himself: Why this 

 activity and how is it controlled? Is 

 this rhythmic contraction of the heart 

 muscles, continuing day after day, year 

 after year, dependent upon factors out- 

 side of the heart, upon stimulations car- 

 ried to it over nerves from other or- 

 gans of the body, or is it of an auto- 



matic nature, depending upon condi- 

 tions and stimulations from within the 

 organ — a function of the very heart 

 cells themselves? The answers have 

 been as many and varied as there have 

 been questions. 



The problem is difficult and compli- 

 cated. That the heart of a cold-blood- 

 ed animal will continue to beat some 

 time after being taken from the body 

 has been observed by almost every one, 

 but this proves nothing. That the 

 activity of the heart is regulated by 

 nerve centers outside of itself is un- 

 doubtedly true, but this in no way con- 

 cerns the cause of the rhythmical con- 

 traction. It is well knowm however, 

 that there are within the organ numer- 

 ous nerve cells which, although cut oflf 

 from their central office, yet through 

 their natural properties might cause the 

 systematic beating. 



The cause may also be sought in the 

 nature of the muscle itself, in wdiich 

 case it is assumed that the muscle cells 

 possess the inherent quality of contrac- 

 tion. Many experiments have been per- 

 formed to solve this interesting prob- 

 lem in a convincing manner. Very 

 recently it has been found possible to 

 grow heart muscles of a warm-blooded 

 animal in an incubator, and during this 

 growth, a single muscle cell has been 

 observed to wander away from the 

 mother tissue and by itself begin to 

 beat. It would therefore seem that the 

 individual isolated cell, having grown 

 to a certain size and finding the neces- 

 sary food, the necessary warmth, the 

 necessary oxygen, or in other words 

 the correct environment, will begin to 

 beat — that is its business, it cannot 

 help it. 



Again, several cells, wdiile growing, 

 may attach themselves one to another 

 forming clusters of various appear- 

 ances, and these cells after a time be- 

 gin to beat, not each one separately but 

 all together, the rythm persisting at 

 perhaps one hundred times a minute 

 for several days. In other cases, where 

 several single heart-muscle cells are 

 unconnected, they will be seen to con- 

 tract, not synchronously but the one 

 independent of the other. These inter- 

 esting observations rather indicate that 

 the heart cells have an inherent ability 

 to contract and must so do when placed 

 in a favorable environment. Rhythmic 



