THE I'RESERVATION OF MARINE ANIMALS. II9 



large quantities at a moderate cost in the form of methylated spirit, 

 which is ethyl alcohol adulterated with methyl alcohol or wood spirit, 

 and other impurities. The adulteration usually causes no difficulties 

 to the zoologist, but it is essential that the methylated spirit should 

 be capable of mixing with water in any proportion without producing 

 any turbidity or any precipitate. 



Modern improvements and refinements in the preservation of 

 marine animals consist in the preliminary treatment of the specimens 

 before they are finally placed in alcohol. The application of alcohol 

 offers dit'ficulties of two distinct kinds. In the first place there are 

 physical difficulties depending on the difference of density between 

 alcohol and water, and the absorption of water by alcohol. These 

 difficulties present themselves in applying alcohol to a dead but 

 otherwise fresh specimen in good condition. Alcohol coagulates the 

 tissues and substance of which the specimen is composed, hardens 

 them, and preserves them from putrefaction or any further change of 

 any kind. But while it hardens thems it rapidly abstracts the water 

 from them, and thus causes soft tissues to contract and shrink until 

 the original shape and appearance of the specimen is entirely lost. 

 To a great extent, or even in some cases entirely, these difficulties 

 may be surmounted by adding the alcohol to the water which con- 

 tains the specimen very gradually, or by the simpler method of 

 placing the specimen successively in mixtures of water and alcohol in 

 different proportions, beginning for instance with a mixture containing 

 ten per cent, alcohol, and ending with one containing seventy or 

 ninety per cent. 



The other difficulties present themselves in dealing with living 

 specimens. The original and primitive method was to plunge the 

 living specimen into " strong spirit," so as to kill it and preserve it 

 at the same time. The consequence of this is that in addition to the 

 distortion and shrinking caused i)hysically by the abstraction of water 

 from the tissues, there occurs a still more violent contraction of all 

 the muscles of the creature, produced by the irritating action of the 

 alcohol on the sensory nerves. A great many of the lower marine 

 animals are endowed with some contracting mechanism particularly 

 adapted to the purpose of withdi awing the more delicate and 

 important organs either into a hard protecting structure, such as a tube 

 or shell, or into the interior of the rest of the body. Such animals 

 are often extremely sensitive, and at the least irritation their beautiful 

 and interesting organs disajipear from view, remaining concealed 



