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CHAPTER III. 



The Preparation of Animal Tissues. 



THE majority of animal tissues require hardening 

 to a greater or less extent, whilst some, on the 

 contrary, must be softened before sections can be 

 cut from them. The various processes for embed- 

 ding and infiltrating organs and tissues have, how- 

 ever, recently been brought to such perfection that 

 not only can much of the hardening once found 

 necessary be dispensed with, much time saved and 

 possible injury avoided, but and this is a very 

 important consideration the risk of distortions and 

 the obliteration of important features and properties 

 in the tissues, which it is all important to their 

 study should be carefully preserved, are reduced 

 to a minimum or altogether avoided by the less 

 heroic and more delicate processes now in vogue. 



Hardening agents, in respect of the effects pro- 

 duced by them upon tissues, &c., form two divisions: 



(1) those (e.g., alcohol and nitric, and picric acids, 

 &c.), which do not interfere with the subsequent 

 processes for staining the tissues and sections; 



(2) those (e.^.j osmic and chromic acids, &c.), 

 which do more or less affect the delicacy of the 

 staining and the action of staining re-agents. 



