1 84 THE STORY OF ANIMAL LIFE 



most convenient fluid 'for the purpose is melted 

 wax. But whereas we might take our sponge out 

 of water, squeeze it dry, and dip it straight into 

 melted wax, we can by no means do so with our 

 animal tissues. For one thing they usually can- 

 not be squeezed, and where they can, they would 

 of course be irretrievably ruined by such a rough 

 process. Even the transference of the specimen 

 from one fluid to another of very different qual- 

 ities and density, would deface the tissues. Cells 

 would burst, or be squeezed out of shape, and or- 

 gans would be loosed from their right position 

 t>y the currents set up in all parts of the specimen, 

 under such circumstances. We must, therefore, 

 try to get rid of the water by degrees. This may 

 be done by gradually adding alcohol, a fluid which 

 may be diluted with water in any proportion. 

 We begin with a comparatively weak solution of 

 alcohol, say about fifty per cent., and immerse the 

 specimen in this for some little time. The time 

 required depends somewhat upon the size of the 

 specimen ; if a large one, a new fluid will take 

 longer to filter through it. Then we must change 

 this solution of alcohol for stronger ones, say 

 seventy per cent, and ninety per cent, successively, 

 and finally to absolute alcohol. By this time the 

 alcohol will have removed almost nearly all trace 

 of water from the specimen. The latter is now 

 nearly but not quite ready to be imbedded in 

 melted wax ; but first we must soak it for a while 

 in a fluid intermediate in thickness between the 

 alcohol and the wax, and capable of mixing in a 

 friendly manner with both. Then it goes into a 

 bath of melted wax, and is kept for hours at a 

 stated temperature until the wax permeates it 

 thoroughly. Then the melted wax and the speci- 



