APP.] IMBEDDING. 249 



it must be hardened with alcohol. We cannot 

 however recommend this substance for embryos. 

 For the method of employing it, see Hand-book 

 for the Physiological Laboratory, p. 92.] 



The exact consistency of these various mixtures 

 should be made to vary according to the solidity 

 of the embryo, by increasing or diminishing the 

 various constituents. 



From a cold solid mass of one of the mix- 

 tures, cut a cubical block (about an inch cube), 

 and on one surface make a shallow cavity, large 

 enough to receive the blastoderm. Having with 

 a morsel of blotting-paper removed all superfluous 

 alcohol from the blastoderm place it quite flat 

 in the cavity just made, and gently pour over it 

 some of the mixture sufficiently heated to have 

 become liquid (care being taken, of course, that 

 it is not too hot). With a heated needle, remove 

 any bubbles that may make their appearance ; and 

 make on the block, as a guide in cutting the sections, 

 a mark of the exact position of the embryo. It is 

 sometimes of advantage to transfer the embryo from 

 the alcohol to some oil of cloves (when the wax and 

 oil is used, or to some creosote, when the paraffin is 

 employed), and to allow it to become saturated 

 with that substance, before placing it in the block. 

 The adhesion of the imbedding material to the 

 object imbedded, is thus rendered more complete. 



This method serves fairly well, when there are 

 no cavities in the object into which it is necessary 

 for the mixture to penetrate. When these exist, 

 the following method (again Dr Kleinenberg's) will 

 be found the most satisfactory. 



Remove the object from the absolute alcohol 

 and place it directly into Bergamot oil, and leave it 

 there, till the oil has completely penetrated through 

 it. In the mean time, prepare a small paper box, 

 by bending up the sides and folding in the corners 

 of a piece of stiff paper, and pour on the bottom of 

 it a thin coating of the mixture of spermaceti and 

 castor oil. When this has become solid, place the 



