PRESERVING AND PREPARING PATHOLOGICAL SPECIMENS. 55 



supporting block, allowing it to project for a sufficient distance beyond 

 the end. The paper is held in place by a rubber baud. We have thus 

 a cylindrical box with a solid bottom projecting below it by which the 

 whole can be held in the clamp of the microtome. 



After the specimen, either free on the end of the block or in its box, 

 is surrounded by celloidin, it should be allowed to stand for a short time 

 exposed to the air, so that the celloidin may harden on the outside by the 

 evaporation of the ether. If the temperature be high, the too rapid 

 evaporation of the ether will cause bubbles to appear in the mass. This 

 should be avoided by covering the specimen with a bell-jar. After the 

 celloidiii mass has acquired sufficient hardness on the outside to keep its 

 shape, the whole should be placed in eighty-per-cent alcohol, in which 

 the celloidiu will harden and acquire a sufficient consistence for cutting 

 in a few hours. When this is accomplished the paper may be stripped 

 off, and .the specimen is ready for sectioning. 



After the sections have been cut they may be stained in the usual way 

 (see below) and mounted in glycerin or balsam. If mounted in balsam, 

 the oil of origanum cretici is used for clearing. 



The uncut portion of tissue may be preserved, embedded in celloidin, 

 by keeping it in eighty-per-cent alcohol. It is better, in permanent 

 preservation of uncut celloidiu -embedded specimens in bulk, to cut them 

 off from the wooden blocks, since alcohol extracts from these a dark 

 resinous material which colors the specimen and interferes with the 

 staining of sections. If glass or vulcanite blocks be used, the whole may 

 he kept in alcohol. 



Stepanoic has recently devised a more rapid procedure in celloidin 

 embedding. The celloidin solution is made by the following formula, a 

 few day being required for dissolving : 



Celloidin, . . 15 gm. 



Oil of Cloves, . . . . .... . .50 c.c. 



Ether, . ' . . 200 " 



Absolute Alcohol, . . . . . . - ... 10 " 



The hardened specimen is transferred from strong alcohol to a small 

 portion of the solution in a closed bottle. In from three to six hours a 

 small piece of ordinary tissue is usually impregnated. It is then put in 

 position on the mounting block and placed in pure chloroform. In this 

 the proper consistency for section cutting is secured in from two to three 

 hours, after which the whole is transferred to eighty-per-cent alcohol. 

 If the specimen remaining after sections have been secured is to be kept, 

 it should be removed from the block and placed in chloroform. 

 For further details of this method, see the original description. ' 

 PARAFFIN. For some purposes, especially when extremely thin 

 though not large sections are required, paraffin embedding is almost in- 

 dispensable. The sections of tissues thus embedded may be cut exceed- 

 ingly thin (2 to 3 /;., or even 1 //, with the Miuot-Blake microtome) and 



1 Stepanow, Zeitschr. f. wissenschaftl. Mikroscopie, Bd. xvii., p. 185, 1900. 



