[11] THE PEESERVATION OF MARINE ANIMALS HOVEY. 



other. It is not necessary to wasb objects which have beeu iu for- 

 malin before transferring them to alcohol. For Idlling and hardening 

 Bhizostoma, Tinia, and some other animals formalin is excellent, and 

 the objects may remain in the fluid a long time before they are trans- 

 ferred to alcohol. It is readily perceived that the contractile animals, 

 when they have been narcotized by one of the usual methods, may be 

 temporarily preserved in formalin in case alcohol is lacking. Colors 

 certainly are preserved for a longer time in formalin than in alcohol, 

 but in time those which are fugitive in one disappear iu the other also. 

 The jjreservative medium has not yet been discovered which will perma- 

 nently preserve the colors which are due to a pigment in the skin or 

 substance of an animal. 



Chromic acid. — Kext to alcohol an aqueous solution of chromic acid 

 is the most useful reagent, and it serves especially for killing and harden- 

 ing gelatinous and soft animals. Objects, however, should not remain 

 in the fluid longer than is necessary, because they become too deeply 

 tinged and are rendered fragile. 



After treatment with the acid it is necessary to wash the animals 

 with fresh water to avoid the formation of a precipitate when they are 

 placed in alcohol. If they are not well washed, they will acquire in 

 time a greenish hue. Chromic acid is used mixed with osmic, acetic, or 

 picric acid, with corrosive sublimate (HgCL), and rarely with alcohol. 

 The solutions are made in ordinary fresh water when possible, though 

 occasionally salt water may be used. They will not; keep long. That 

 which has served once may be used again if it will not be too dilute 

 when added to the water containing the animal and if too much time 

 has not elapsed. When the solution has turned green after standing 

 it is not fit to use. 



Acetic acid. — This is a reagent which has the property of permeating 

 tissues instantly and hardening them, and it is a very efficacious means 

 of rapidly killing contractile animals, but it has the disadvantage of soft- 

 ening them again if they remain in it too long a time. Objects remain 

 relatively transparent. In certain cases it is necessary to use a con- 

 centrated solution of the acid. It is often mixed with chromic acid for 

 killing and hardening noncontractile transparent animals. 



Osmic acid. — In general, osmic acid is not used as much now as 

 formerly, because its use has several inconveniences. Efforts have 

 been made at the station to substitute other reagents for it, and in 

 many cases they have been successful. It hardens gelatinous forms 

 well and preserves the transparency sufficiently, but its action is too 

 great eventually. The preparations become dark- colored and are ren- 

 dered fragile; consequently they should remain only until they have 

 acquired a light brown tint.' Before they are transferred to alcohol 



'Dr. Paul Mayer's method for bleaching objects which have been too much black- 

 ened is not jjracticable for soft animals, since it softens them too much. (Mitth. Zool. 

 Stat. Neapel, II, 1880, p. 8.) 



