346 PRESERVATION OF MARINE ORGANISMS 



important factor in the success of fixation is the quick 

 penetration of the chemicals through the tissues. Slow 

 penetration gives time for the innermost cells or tissues 

 to undergo post-mortem changes before they are 

 properly fixed. 



The preservation of an animal after death, or of its 

 tissues after fixation, is the final stage in the prevention 

 of decay. The preserving fluids commonly used are 

 either formalin or alcohol, and their preserving action 

 should be understood. We take as an example a big 

 jelly-fish, the jelly of which is more than 90 per cent, 

 water. When alcohol is used as the preserving fluid, 

 all the water in the jelly has to be turned out, and 

 alcohol of a different strength substituted. The first 

 bath of alcohol is considerably reduced in strength by 

 the water from the jelly. Fresh alcohol is then sub- 

 stituted, and this second bath becomes less diluted. 

 The changing of the alcohol must go on until one is 

 sure that the specimen is thoroughly saturated with 

 alcohol of at least 70 per cent, strength. Weak solu- 

 tions of alcohol have no preserving qualities, and are 

 not proof against bacteria. 



Formalin, on the contrary, is a watery fluid, and it 

 has simply to mix with the watery fluids inside the 

 jelly. During the process of mixing its original 

 strength is lessened by dilution, as in the case of 

 alcohol, and a certain quantity is used up in chemical 

 action on the tissues. But so long as there is a small 

 percentage of formalin present the jelly is safe against 

 decay, owing to the powerful antiseptic properties of 

 formalin. 



