ALCOHOL 355 



least once. Transfer from 50 per cent, to 70 per cent. 

 The passage through these different grades of alcohol 

 reduces the amount of shrinkage, and gradually re- 

 moves the watery fluids from the body of the animal. 

 It is very important for all the tissues of the body to be 

 thoroughly permeated with 70 per cent, alcohol, hence 

 the necessity of changing at least once the 70 per cent, 

 solutions. As weak solutions of alcohol quickly pro- 

 duce maceration of the tissues, it is advisable not to 

 leave specimens too long in the weak grades. 



Alcohol which has become weakened by water from 

 the animals soaked in it (so long as it does not contain 

 chemicals) should be kept, and coarse animals — 

 Crustacea, fish, starfish, etc. — can have their first 

 brief soaking in this before being transferred to stronger 

 alcohol. An alcoholometer is useful here. This spirit 

 should be thrown away when of a less strength than 

 30 per cent. But if it is not necessary to economize 

 alcohol, then animals with hard coats, such as crabs, 

 or with firm bodies, such as fishes, can be placed at 

 once in yo per cent. ; after a preliminary soaking 

 the alcohol must be changed. The number of changes 

 required depends upon the size of the animal and the 

 quantity of alcohol used for each bath. The most 

 important thing is to keep up the strength of the final 

 solution, and not to store away the specimens until 

 they have become thoroughly permeated with at least 

 70 per cent, alcohol. 



It is well to remember that the weakest grade of 

 alcohol is the heaviest, and remains at the bottom of 

 the vessel. When passing specimens through dif- 

 ferent strengths of alcohol, an occasional stir up should 

 be given, just to help on the process of mixing, and 

 to bring the stronger alcohol into contact with the 

 specimens. 



