304) APPENDIX 



When the tissue is to be cut as soon as imbedded, the carrier of 

 the microtome may be used instead of the piece of cork. And instead 

 of fixing the tissue to cork, it may be placed in a paper case, celloidin 

 poured over it, and the case after a short time put in chloroform or 

 85 p.c. alcohol; as soon as the outer part is firm, the paper should 

 be removed. 



If the object is large, it is placed in a small dish covered up 

 but so as to allow a very gradual evaporation of the solvents ; 

 when the celloidin is fairly firm a fresh coat is added, and the 

 process repeated until there is sufficient firm celloidin around 

 the object. A block with the object is then cut out and the 

 hardening completed with chloroform. 



If the block is not sufficiently transparent it may be cleared 

 by placing it in a mixture of equal parts of cedar- wood oil and 

 chloroform. 



Fixing to the carrier of the microtome. The imbedded tissue 

 is either fixed directly to the carrier of the microtome, or to 

 a piece of wood which can be attached to it, or take its place. 



A layer of thick celloidin is spread over the wood and allowed 

 to dry ; the imbedded tissue is cut away from the cork, so as to 

 give a clean surface of celloidin, this surface is moistened with 

 absolute alcohol and ether ; the dry celloidin on the wood is 

 similarly moistened ; a drop of thick celloidin is placed on it, 

 and the tissue-block is lightly pressed into the drop. In a 

 minute or two the whole is dipped into chloroform for a quarter 

 of an hour or more. 



Cutting. The razor is fixed obliquely so that it passes from 

 heel to point through the tissue. The razor and the tissue are 

 moistened with 80 to 95 p.c. alcohol, and the sections as soon as 

 cut are placed in this fluid. If the celloidin has been cleared 

 with cedar-wood oil and chloroform, cedar- wood oil with a little 

 chloroform should be used in place of alcohol. 



In the case of a large piece of tissue it is sometimes advisable 

 to brush over the exposed surface with a dilute celloidin solution 

 before cutting each section. 



Staining sections. The sections still permeated by celloidin 

 may be stained with any reagent. But most aniline dyes stain 

 the celloidin also. For such dyes the celloidin should be dissolved 



