THE NERVOUS SYSTEM AND ITS 

 CONSERVATION 



CHAPTER I 



INTRODUCTION 



TISSUES 



BEFORE the modern microscope was available, anato- 

 mists and physiologists recognized in the make-up of the 

 human body various types of constituent substance or 

 fabric. The different kinds of material recognizable 

 were few in number and easily assigned to certain large 

 classes. Comparison of one part of the body with another 

 showed that the same forms of organized substance were 

 found over and over again. The several varieties of 

 material distinguished came to be known as tissues. 



In the hand, for example, we find the skin, the muscle, 

 and the bone, representatives of kinds of tissue con- 

 trasted in function, in physical character, and in chemical 

 composition. Closer study of the hand would add other 

 members to the list. When we consider the tissues with 

 regard to the intensity of the life-processes taking place 

 in them it is clear that this is anything but a constant 

 quantity. In some cases we have to do with structures 

 which are essentially passive in their nature and which 

 might conceivably be replaced by non-living substitutes. 

 This is true of those tissues which are described as con- 

 nective. Their service is mechanical; they unite and sup- 

 port other tissues. Bone is a conspicuous example of 



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