XIV TO THE TEACHER. 



studied, look at the brain case, etc. The bones by them- 

 selves are a pretty dry subject; and the teacher must not 

 allow the class to lose its interest for one day even, or he 

 may never recover that interest. 



Order of Topics The order of topics is a most important 



matter in the study of physiology. We should not only try 

 to begin with the study in such a way as to get and hold the 

 interest ; the topics ought to be arranged in such an order that 

 beginning with what is simple we may proceed by an easy and 

 natural gradation to that which is more difficult, so that the 

 earlier topics shall prepare the way for the latter. Of course 

 the study of any part of the body throws light upon the study 

 of every other part. Still, it is possible to make such arrange- 

 ment that the topic presented first be of such a nature as best 

 to explain itself, to stand alone, so to speak, and to leave till 

 later the study of actions that directly depend on many others, 

 and that cannot be explained without introducing those others. 



For example, suppose we were to begin with the digestion, 

 which is often presented as the first of the fundamental, vital 

 processes of the action of the body (the bones and muscles, 

 perhaps, having had a little attention). 



In the study of digestion we are met by the action of 

 muscles in masticating the food, in swallowing, and through- 

 out the whole digestive tube. Shall we leave the explanation 

 of muscle action, or stop and take it up ? 



Saliva is poured upon the food in the mouth. Shall we 

 stop and explain the action of a gland ? This involves a 

 knowledge of circulation. To understand how the gland gets 

 more blood at this time, out of which to make the saliva, we 

 must understand the action of the muscles in the walls of the 

 arteries supplying the gland. To understand the control of 

 these muscles we must know considerable of the nervous sys- 

 tem. And so on throughout the whole process of digestion. 



