METHODS OF EMBEDDING. 295 



supports for the embedded specimen, but blocks of hard wood may 

 be used in their place. 



For the support of tissues embedded in collodion blocks of plate- 

 glass are probably both better and cheaper than those made of other 

 materials. They may be easily prepared from waste pieces of plate- 

 glass, about a quarter of an inch thick, and " obscured " or ground on 

 one surface. The glass may be cut into blocks of any desired size by 

 scoring the smooth side with a diamond and then splitting the pieces 

 apart with a sharp blow from a wedge-shaped hammer. The em- 

 bedded specimen is affixed to the rough surface of these blocks by 

 means of collodion, and the blocks may be numbered with a lead 

 pencil upon the rough surface. The writing will be preserved from 

 obliteration by the specimen subsequently placed upon it, and can 

 be read through the glass. 



1. Embedding in Collodion (or Celloidin). — Tissues of firm con- 

 sistency and moderately uniform structure, such as liver, kid- 

 ney, and the majority of tumors which have been hardened, 

 may be embedded without previous impregnation. Before this 

 can be done, however, they must be either dehydrated with abso- 

 lute alcohol, or soaked for a few hours in a mixture of equal 

 volumes of ether and alcohol (95 per cent, alcohol will answer, 

 if absolute alcohol is not to be had). For this rapid method the 

 bottom of the piece of tissue must be flat and parallel to the plane of 

 the desired sections. When the necessary trimming of the speci- 

 men is completed moisten it with absolute alcohol or the ether- 

 alcohol mixture, then dip it in the thick solution of gun-cotton and 

 place it at once upon the ground surface of the glass block (pre- 

 viously labelled). In a few minutes the collodion will have evap- 

 orated sufficiently for the formation of a distinct pellicle upon its 

 surface. When this has become firm enough to withstand gentle 

 pressure immerse the block and specimen in several times their vol- 

 ume of 80 per cent, alcohol. This will harden the collodion, and in 

 the course of a few hours the specimen will be ready for cutting. 



Tissues impregnated with collodion had best be embedded by a 

 slower process than the foregoing, although that method will answer 

 where only a slight support of the tissue-elements within the speci- 

 men is needed. A gradual concentration of the collodion within 

 the tissues may be brought about in the following manner : 



Smear the inside of a small, straight-sided glass dish with a trace 

 of glycerin and then fill it with enough moderately thick collodion 



