THE PARAFFIN PROCESS I67 



In all cases the amount of fluid must be greatly in excess. It 

 is useless merely to cover the block with the spirit. 



Clarification. — In the next step the alcohol is removed from the 

 tissue and replaced by some fluid which will dissolve paraffin. 

 Fats are dissolved out from the tissues at this stage. 



This step is also very simple. The blocks are passed directly 

 from absolute alcohol into chloroform, and allowed to remain 

 there for twelve to twenty-four hours, according to their size. It 

 is not necessary to use a preliminary bath of a mixture of alcohol 

 and chloroform. 



It is a good plan to place the bottle containing the block in a 

 warm place with the cork out for an hour or so before proceeding 

 further, as by so doing the last traces of the alcohol will be removed. 



Infiltration with Paraffin. — This is the stage which presents most 

 difficulties to the home-worker, for it is necessary to keep the 



Fig. 40. — L-sHAPED Moulds for embedding in Paraffin. 



block of tissue soaked in paraffin which is just melted for at least 

 twelve, and more often twenty-four, hours. To do this properly 

 involves the use of some sort of incubator. This might possibly 

 be rigged up out of a tin biscuit-box in the manner already 

 described, though considerably more heat would be necessary, as 

 the paraffin melts at about 50° C. But the writer has often 

 embedded the blocks by placing them in bottles containing the 

 paraffin at such a distance from the fire that the paraffin is never 

 completely melted, but always shows a thin solid layer on the 

 surface. To do this it is only necessary to look at the bottle 

 occasionally, and move it a little further from the fire if the 

 paraffin is completely melted, and vice versa. The process may 

 be stopped at night without any harm resulting, and if the soaking 

 only continues for a few hours at a time it is of no consequence so 

 long as the total period is made up. 



Casting the Bfocfa.— Special metal moulds are used in the labora- 

 tory (Fig. 40). A pill-box will do quite well. A small amount of 

 melted paraffin is poured into the box, and the piece of tissue is 



