C12 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [6] 



and for sucli cases recommeuds boiling absolute alcohol, whicli kills in- 

 stantly. For tracheata (insects) this is often the ouly means by which 

 the dermal tissues can be well preserved, as cold alcohol penetrates too 

 slowly." 



It will be profitable to lay down the following general principles re- 

 specting the use of alcohol : 



(1) In almost all cases ivJiere soft tissues or objects are to be prepared, 

 eithtr for museum or histological purposes, it is best to at first immerse 

 the object in weak alcohol, and to gradually increase its strength so as to 

 extract the water of organization by degrees, and thus avoid the injurious 

 shrinlage and distortion due to the use of too strong a mixture. 



(2) Sometimes it is desired to preserve a very large, soft object in 

 alcohol, but, at ordinary temperatures, decomposition often begins in 

 the center of the object before the alcohol has had time to completely 

 saturate the object. Decomposition of this sort may be hindered and 

 even prevented by placing the vessel containing the object in moder- 

 ately strong alcohol in a refrigerator kept at a little above freezing. 

 This prevents decomj)osition, and gives the alcohol time to saturate 

 the object. Any other hardening agent may be applied in the same 

 way to large objects, but in such cases care must be taken that the 

 solution is not frozen during the process. Solutions of Miiller's fluid 

 or chromic acid may be frozen; alcoholic solutions not so readily, unless 

 they are very dilute. 



We have considered alcohol first as a preservative, hilling, and hard- 

 ening agent, because it is the best known and most generally used and 

 has not yet been superseded by any of the many compounds which 

 have been suggested as substitutes, mainly on the score of their cheap- 

 ness. 



Midler'' s fiuid. — For convenience this compound probably ranks next 

 in value to alcohol, as a temporary preservative agent and as a harden- 

 ing fluid. The formula for its preparation is as follows : 



Bicliromate of potasli 5 parts. 



Sodic aulpliate 2 " 



Distilled water 200 " 



This makes an orange-colored solution in which embryos, small animals, 

 and pieces of tissue may be preserved for histological i^urposes. And 

 it possesses one important advantage over chromic acid in this, that the 

 object may be left in it for a month without injury, although it darkens 

 albuminous substances permanently like chromic acid and may be ob- 

 jected to by some on tbis account. Nevertheless, it is a very convenient 

 preservative compound in cases where the care and attention required 

 in the use of better reagents cannot be applied to the preservation of 

 such materials on account of their numbers or when the collector is 

 traveling, with ouly occasional opportunities for overliauling and caring 

 for his collections. 



