The Blood and its Circulation 159 



read the existence of the " tobacco heart," an affection 

 recognized by all medical men. It is claimed that one in 

 every four of tobacco users is subject, in some degree, to 

 this disturbance. Test examinations of a large number 

 of young men who used cigarettes showed that only a very 

 small percentage escaped cardiac trouble. 1 



ADDITIONAL EXPERIMENTS 



Experiment 67. To show how blood holds a mineral substance in 

 solution. Put an eggshell crushed fine into a glass of water made 

 acid by a teaspoonful of muriatic acid. After an hour or so the egg- 

 shell will disappear, having been dissolved in the acid water. In like 

 manner the blood holds various minerals in solution. 



Experiment 68. To hear the sounds of the heart. Locate the 

 heart exactly. Note its beat. Borrow a stethoscope from some 

 physician. Listen to the heart beat of some friend. Note the sounds 

 of your own heart in the same way. 



Experiment 69. To show how the pulse may be studied. The 

 movements of the artery in the human body as the pulse wave passes 

 through it may be shown to consist in a sudden dilatation, followed by 

 a slow contraction, interrupted by one or more secondary dilatations. 

 This demonstration may be made by pressing a small piece of looking- 

 glass about one centimeter square (two-fifths of an inch) upon the 

 wrist over the radial artery, in such a way that with each pulse beat 

 the mirror may be slightly tilted. If the wrist be now held in such a 

 position that sunlight will fall upon the mirror, a spot of light will be 

 reflected on the opposite side of the room, and its motion upon the 

 wall will show that the expansion of the artery is a sudden move- 

 ment, while the subsequent contraction is slow and interrupted. 

 BOWDITCH'S Hints for Teachers of Physiology. 



1 Tobacco, and especially cigarettes, being a depressant upon the heart, 

 should be positively forbidden. DR. J. M. KEATING on "Physical 

 Development," in Cyclopedia of the Diseases of Children. 



