INFILTRATION WITH PARAFFIN. 193 
changed into stronger spirit and so on until absolute 
alcohol is reached. The slower this process is carried 
out the better will be the results; in practice the 
strengths of the successive lots of spirit used may be 
40 per cent., 75 per cent., and the strong methylated 
spirit, and the block may remain in each for twelve 
hours. Lastly, it goes into two successive lots of 
absolute alcohol. 
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 until they appear translucent. 
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 block 
) 
