BY II. VON LENDENFELD, PH.D. 257 



Like other specimens, these also should be kept in strong non- 

 methylated spirits of wine (70-80%), or in a mixture of alcohol 

 and glycerine. But if they were placed in such a liquid immedi- 

 ately on being caught, they would shrink to a shapeless mass and 

 be useless. It is therefore necessary to harden them before placing 

 them there. This hardening can be effected by the aid of com- 

 pounds of heavy metals which act chemically on the Protoplasm 

 in the cells, and harden it, thereby hardening the whole specimen. 

 The metal itself, or its Oxide, is frequently precipitated in the 

 Protoplasm, causing the whole to turn a dark colour. 



Osmic Acid, Chromic Acid, Chloride of Gold, Chloride of 

 Palladium, Chloride of Quicksilver, Nitrate of Silver, and Chloride 

 of Iron, are used for the above-mentioned purposes. 



The solutions in use are very weak, from - 2 to 1% in 

 strength, and the animal is immersed in them directly after 

 having been removed from the seawater. The different solutions 

 are allowed to act for some time, from one second to an hour or 

 more as the case may be. Then the specimen is well washed in 

 fresh water and placed in weak spirits (30 or 40%.) It is left 

 there a short time, then placed in stronger spirits, and finally 

 put into the strong spirits, (70-80%.) 



Different solutions are used to gain different ends. Osmic Acid 

 preserves the Epithelia wonderfully, whilst Chloride of Gold and 

 Picric Acid have a greater effect on that sort of Protoplasm which 

 is met in Ganglia cells and Nerves, wherefore these are often used 

 for the purpose of studying the latter. Chloride of Mercury 

 (corrosive sublimate) is very much used and greatly recommended 

 by many. Chromic Acid or Bichromate of Potassium, make the 

 Frotoplasm yellow, and coagulate it in such a manner as to 

 make it perfectly intransparent. Very transparent animals can, 

 therefore, be made better visible by Chromic Acid. It must be 

 used in very weak solution, and particularly carefully washed 

 out before the specimens are placed in spirits. It preserves 

 Epithelia exceedingly well, and is very useful to put fish in before 

 preserving them in spirits. 



