4O PHYSIOLOGY. 



eighty. At birth the rate is from one hundred and thirty 

 to one hundred and forty, and gradually decreases till 

 about the age of twenty, when the average of seventy-two 

 is reached. This rate holds till old age, when it increases. 

 The rate is increased by muscular activity, food, external 

 heat, internal heat (fever), pain, and mental excitement. 

 Music accelerates the pulse rate. The pulse rate varies 

 during the twenty-four hours, being lowest during the 

 night, and highest about 1 1 A.M. Certain diseases increase 

 the frequency of the pulse. Some drugs quicken the 

 pulse rate, and others dimmish it. 



The Heart Beat and the Pulse. i . The heart beat, felt at the left 

 of the breast bone. 



2. The pulse, felt at the wrist and at various parts of the body. 

 Perhaps the most convenient place to study it is at the temple. Lay 

 the forefinger lightly along the cheek just in front of the ear. Count 

 the pulsations for a minute. 



Let one or two pupils who are quick at figures step to the blackboard 

 and put down the number of pulsations of each pupil, and divide by the 

 number thus reporting, to get the average. 



1 . Let all in the class count the pulse while sitting. Probably it 

 will be best to discard the first trial, as there are likely to be several 

 failures from one cause or another. Then, too, there is usually a slight 

 excitement at the beginning of a wholly new experiment. Get the aver- 

 age of the class. 



2. Find the pulse while sitting; rise quickly, and immediately begin 

 to count the pulse. Compare with the pulse as taken while sitting. 



3. Compare the pulse before and after meals. 



4. With the thumb and finger lightly clasp the windpipe, well back. 

 The pulse in the carotid arteries will be felt. 



The Position of the Heart. The base of the heart is 

 in the center of the chest, just back of the breast bone, but 

 the apex points downward and to the left. 



The Covering of the Heart. The heart is inclosed in 

 a loosely fitting membranous bag, the pericardium. Within 



