fluid, which attacks the calcareous portions and causes them 

 to lose form or brilliancy, or both. In the case of large 

 animals, such as fish, one must make an injection through the 

 anus of a solution of at least 5 per cent strength. With for- 

 malin, as with other preservatives, only one, or at any rate 

 only a very few, objects should be put into the same receptacle 

 at the same time, and there must be a good amount of fluid in 

 proportion to the animal matter present. For gelatinous animals 

 the solution should be of 1 to 4 per cent strength. Carmarina 

 and similar things may be killed and hardened at the same time 

 by the use of formalin of the right strength and chromic acid 

 of 1 per cent in equal parts. For animals of some consistency, 

 like ascidians and fish, one should use a 2 to 6 per cent forma- 

 lin solution, the general rule being that the softer the animal 

 the weaker the formalin. Either fresh or salt water may be used 

 in making the solutions, as may be convenient. The sea water 

 solution, indeed, preserves the transparency of gelatinous bodies 

 better than the other. It is not necessary to wash objects which 

 have been in formalin before transferring them to alcohol. For 

 killing and hardening Rhizostoma, Tima, and some other animals 

 formalin is excellent, and the objects may remain in the fluid 

 a long time before they are transferred to alcohol. It is readi- 

 ly perceived that the contractile animals, when they have been 

 narcotized by one of the usual methods, may be temporarily pre- 

 served 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 in the other 

 also. The preservative medium has not yet been discovered which 

 will permanently preserve the colors which are due to a pigment 

 in the skin or substance of an animal. 



Chromic acid . — Next to alcohol an aqueous solution of 

 chromic acid is the most useful reagent, and it serves especially 

 for killing and hardening 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 the 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 (HgCl2 

 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 contain- 

 ing the animal and if too much time has not elapsed. When the 

 solution has turned green after standing it is not fit to use. 



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