METHODS OE COLLECTING AND 
PRESERVING VARIOUS INVERTEBRATE 
ANIMALS. 
I. GENERAL. 
Alcohol is indispensable as preservative fluid; but certain pre¬ 
cautions are necessary in its use. Except in a very few cases it is 
unnecessary to use it in its full strength, 70 per cent, being quite 
sufficient for preservation, and producing much less contraction and 
fragility in delicate organisms. Strong alcohol should be reduced 
with distilled water to the desired strength, as ordinary spring-water 
frequently contains a sufficient amount of carbonate of lime and 
other substances in solution to give a cloudy precipitate, which may 
effectually destroy the appearance of a specimen. 
Furthermore, it is desirable that animals should first be placed in 
weak alcohol (from 35 to 50 per cent.) for from two to six hours. 
Some of the weak spirit should then be drawn off and stronger 
added until the desired strength is obtained. With delicate gelatinous 
structures the increase in the strength of the alcohol should be as 
gradual as possible. The process of placing specimens successively 
into alcohols gradually increasing in strength is known as l; grading.” 
Formalin or formal has been much used of late years on account 
of its portability and cheapness. Commercial formalin is a 40 per 
cent, solution of formaldehyde in water. The strength of formalin 
now most recommended for general purposes is a 10 per cent, solu¬ 
tion (i.e. 4 per cent, formaldehyde), made by diluting one part of 
commercial formalin with nine parts of water. The mixture, when 
used for preserving, should be poured away after 24 hours, and fresh 
solution added; and, further, the bottles should be securely sealed. 
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