74 HUMAN PHYSIOLOGY 



by the organ in say twenty-four hours. This amounts 

 to what in scientific language is called one hundred 

 and twenty foot-tons of work. Put in plain language 

 this statement means that if all the work expended 

 by the heart in twenty-four hours could be gathered 

 up, concentrated, and applied to a huge lift, it would 

 raise one hundred and twenty tons one foot off the 

 ground. 



THE HEART AND THE NERVOUS SYSTEM. It is a 

 familiar fact of life that the movements of the heart 

 are influenced by our emotions. The poet speaks of 

 the " pulse of hope," and it is undeniable that when 

 an individual is happy, contented, and healthy, his 

 heart beats freely and with vigour. On the other 

 hand, the play of a different emotion, such as grief, 

 acts in the opposite direction. The heart beats then 

 become of a slower character, and the circulation is 

 carried on less vigorously. The heart is well under 

 the control of the nervous system, but it is necessary, 

 in order fully to appreciate the relations between the 

 two sets of organs, to remind ourselves that in addi- 

 tion to the brain system, composed of the brain itself, 

 the spinal cord, and the ordinary nerves of the body, 

 a second nervous system exists in the shape of the 

 sympathetic system which lies in front of the spine. 

 This latter system controls actions in the body which 

 are independent of the will, and amongst other duties 

 it performs, it is responsible for controlling the 

 ordinary work of the heart. Four sets of nerves are 

 concerned with the Jjeart and its regulation. Imbed- 

 ded in the substance of the heart we find masses of 

 nerve cells belonging to the sympathetic system, 

 termed cardiac or heart ganglia. These represent 

 the heart's own little government system, so that we 

 might very well compare the organ to a territory like 



