NERVOUS TISSUES. 



Nervous tissue presents for chemical study the following 

 classes of substances: 



1. Proteins two ordinary cell globulins coagulating at 

 45 C. and 75 C., and a nucleoprotein. 



2. Lipoids bodies of a fatty nature, including the leci- 

 thins, cerebrosides, and protagon. It is somewhat question- 

 able whether the latter substance is a unit or a mixture of 

 lecithins, cer^brin, and proteins. 



3. Cholesttrols and fatty acids. 



4. Neurokeratin a substance apparently related to ker- 

 atin. 



5. Extractives the same as those of muscular tissue. 



LIPOIDS. 



The lipoids, together with the cholesterols, are usually 

 classed as the myelin bodies from the fact that they exist as 

 a mixture in the so-called myelin substance of the medulla. 

 They contain fatty acid radicals in their molecule, and on 

 this account are closely related to the fats and sometimes 

 are classified under them.- For the sake of convenience in 

 isolation for study they will be considered here, although it 

 must not be forgotten that the lecithins are widely distributed 

 in all forms of living tissues and belong to the primary con- 



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