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 softening them again if they re- 

 main in it too long a time. Objects remain relatively trans- 

 parent. In certain cases it is necessary to use a concentrated 

 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 rendered fragile; 

 consequently they should remain only until they have acquired 

 a light brown tint. Before they are transferred to alcohol 

 they should be washed for some minutes in fresh or distilled 

 water, as should be done with all animals which have been treat- 

 ed with any mixture containing osmium. 



Kleinenberg ' s liquid was one of the first adopted at 

 the Zoological Station for the preservation of marine forms. 

 Since it presents the disadvantage of staining the alcohol, 

 even after repeated washings, and of not hardening the animals 

 sufficiently, its use has been given up little by little, until 

 now it is confined to the preparation of histological subjects, 

 with the single exception of Balanoglossus, which is killed 

 with this solution for exhibition as well as for study. 



Lactic acid , in a solution of one in a thousand in sea 

 water, serves well in treating larvae and small gelatinous 

 organisms. 



Hydrochloric , pvroligneous , and sulphuric acids are 

 used rarely. 



Corrosive sublimate , recommended first by A. Lang, is 

 much used as a fixing agent, because it has the property of 

 permeating tissues rapidly and hardening greatly. It is used 



Dr. Paul Mayer's method for bleaching objects which have been 

 too much blackened is not practicable for soft animals, since 

 it softens them too much. (Mitth. Zool. Stat. Neapel, II, 1880, 

 p. 8.) 



2 Kleinenberg's liquid is made by mixing 100 c.c. of a saturated 

 aqueous solution of picric acid with 2 c.c. of concentrated sul- 

 phuric acid. Filter and add three volumes of distilled water. 



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