236 THE MICROSCOPE. 



CHAPTER XII. 



<* 



THE USE OF THE MICROSCOPE IN THE STUDY OF 

 PHYSIOLOGY. 



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 com- 

 posed 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 mi- 

 nute organs renders possible and no more. 



2. The Necessity of the Microscope. If, there- 

 fore, we would know the real structure of the human 

 body, we must make use of the microscope. We are not at 

 liberty either to use it or not ; we must have recourse to it 

 in order to obtain a real knowledge of the human body. 

 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 

 intelligence ; 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, 



3. Convex lenses, or magnifying glasses, are disks 

 of glass or other transparent substance, which have the 



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

 Amount of duty performed by the liver? 



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



3. What are convex lenses? Kind of lenses used in microscopes? Experi- 

 ment ? Picture thrown upon the eye ? Derivation of the word microscope * 



