METHOD XIX. 



FORMALIN FOR PURPOSES OF DISSECTION. 



An application of formalin for the fixation and preservation 

 of specimens for dissection. May be applied to the whole or 

 any part of the animal for the dissection of any of its tissue, 

 but is especially adapted for the central nervous system. 



Directions for the removal of the central nervous system. 



ADVANTAGES OP FORMALIN. 



To make a satisfactory and detailed dissection of any 

 specimen, and especially of the central nervous system of the 

 larger animals, the following conditions are essential: 



1. The specimen should possess a greater rigidity and 

 resistance to handling than its natural softness in the fresh 

 state will allow. 



2. The normal shape and color of the specimen should be 

 preserved as far as possible, and shrinkage avoided. 



3. The hardening process should result in the greatest pos- 

 sible amount of toughness and elasticity, so that the specimens 

 may not only be sectioned without danger of breaking or 

 crumbling, due to brittleness, but also may permit of the 

 greatest possible extent and ease in tearing and teasing apart 

 its different structures, for torn preparations are often more 

 instructive than sections. 



4. The gross structural and optical differences between the 

 different tissue elements should be maintained in the specimen. 

 " White substance " should be readily distinguishable from 

 "gray substance," so that a nerve pathway may be easily fol- 

 lowed in the central nervous system. Also in the peripheral 

 system the conditions should be such that the course of a 

 nerve may be easily followed. 



5. The preserving fluid should be of such a nature that 



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