CHAPTER XII 



THE USE OF THE MICROSCOPE IN THE STUDY 

 OF PHYSIOLOGY 



The Law of Tissues Necessity of the Microscope Different Kinds of 

 Microscopes Additional Apparatus Preliminary Studies The 

 Study of Human Tissues Tissues of the Inferior Animals Incen- 

 tives to Study 



1. The Law of the Tissues. The will of an infinite Creator 

 is obeyed by atoms as well as by worlds. He has seen fit to 

 commit all the functions of life to structures or tissues so small 

 as to be invisible to the naked eye. A muscle, for example, as 

 we have already learned, is composed of innumerable filaments, 

 visible only by the aid of the microscope; and the power of 

 the muscular mass is but the sum of the contractile power of 

 the filaments which enter into its composition. Again, each 

 cell of the liver, invisible to unassisted sight, is a secreting 

 organ, and the liver performs as much duty as the sum of these 

 minute organs renders possible. 



2. The Necessity of the Microscope. If, therefore, we would 

 know the real structure of the human body, we must make use, 

 of the microscope. Our eyes are constructed for the common 

 offices of life, to provide for our wants and guard us from the 

 ordinary sources of danger ; but by arming them with lenses, 

 the real structure of plants and animals is revealed to our intel- 

 ligence ; and enemies, otherwise invisible, that lie in wait in 

 the air we breathe, and in our daily food and drink, to destroy 

 life, are guarded against. 



1. The will of the Creator, by what obeyed ? The power of a muscle ? Amount of duty 

 performed by the liver ? 



2. Necessity for using the microscope ? The advantages gained by its use f 



