IV.] ON ELEMENTARY INSTRUCTION IN PHYSIOLOGY. 89 



sciences, is eminently characteristic of physiology 

 the difficulty of the subject begins beyond the stage 

 of elementary knowledge, and increases with every 

 stage of progress. While the most highly trained and 

 the best furnished intellect may find all its resources 

 insufficient, when it strives to reach the heights and 

 penetrate into the depths of the problems of physiology, 

 the elementary and fundamental truths can be made 

 clear to a child. 



No one can have any difficulty in comprehending 

 the mechanism of circulation or respiration; or the 

 general mode of operation of the organ of vision ; 

 though the unravelling of all the minutiae of these 

 processes, may, for the present, baffle the conjoined 

 attacks of the most accomplished physicists, chemists, 

 and mathematicians. To know the anatomy of the 

 human body, with even an approximation to thorough- 

 ness, is the work of a life ; but as much as is needed 

 for a sound comprehension of elementary physiological 

 truths, may be learned in a week. 



A knowledge of the elements of physiology is not 

 only easy of acquirement, but it may be made a real 

 and practical acquaintance with the facts, as far as it 

 goes. The subject of study is always at hand, in 

 oneself. The principal constituents of the skeleton, 

 and the changes of form of contracting muscles, may 

 be felt through one's own skin. The beating of one's 

 heart, and its connection with the pulse, may be noted; 

 the influence of the valves of one's own veins may be 

 shown; the movements of respiration may be observed; 

 while the wonderful phenomena of sensation afford an 



