352 PRESERVATION OF MARINE ORGANISMS 



be taken : Formaldehyde 30 per cent., 1 part ; water, 

 6J parts. This solution contains formalin 13-3 per 

 cent., and is equivalent to formaldehyde 4 per cent. 



Some animals can be killed at once by dropping 

 them into formalin 10 per cent., or by pouring the 

 solution into the sea water containing the animals ; 

 but others are not killed quickly enough, and have 

 sufficient time to contract or to cast off appendages. 

 For the latter class of animals either an anaesthetic, 

 like cocaine, may be used before adding the formalin, 

 or another chemical, like picric acid, added to the 

 formalin, to quicken the killing action. 



The value of formalin in fixation is to prevent 

 shrinkage, and for this purpose it has been added with 

 success to several well-known fixative formulae. 



Alcohol. — The alcohol used for preserving purposes is 

 pure methylated spirit, known as Industrial methylated 

 spirit, upon which excise duty must be paid within the 

 limits of the British Excise, or an exemption permit 

 obtained from the Custom House, London. The 

 ordinary methylated spirit obtained from a dealer is 

 quite useless for preserving marine animals, as it con- 

 tains certain chemicals, put in to prevent people from 

 drinking it. Directly water is added to this liquid it 

 takes on the appearance of milk, and a very fine pre- 

 cipitate is thrown down. All attempts to get rid of 

 this precipitate are only waste of labour, as an 

 additional drop of water starts a fresh precipitate in a 

 filtered solution. 



Pure methylated spirit when purchased is commonly 

 called " 90 per cent, alcohol/' though its strength may 

 be slightly greater than go per cent. This may be 

 diluted with water so as to make up solutions con- 

 taining 30 per cent., 50 per cent., and 70 per cent, of 

 alcohol. These solutions can either be made up by 



