674 SUMMARY OF CURRENT RESEARCHES RELATING TO 



and press over it a tiny piece of cover-glass. This causes a perfect 

 transparence on the top of the cell and makes the enclosed specimen 

 visible. The only special advantage of having the cell polished is to 

 enable one to determine quickly the position of the specimen within. 

 An advantage of leaving the cell with ground sides is that the number 

 and name of the specimen may be written easily upon the surface with 

 India ink. 



This slide-cell, though chiefly intended for minute insects and parts 

 of insects, may also be used for Crustacea, Arachnida, Rhizopoda, 

 Vermes, etc. 



The method of use is very simple : it is only necessary to select a 

 slide-cell of suitable calibre, fill it with xylol-balsarn, and then push it 

 in the preparation. The ends of the tube are then cemented up. 



(6) Miscellaneous. 



Removing Over-hardening in Anatomical and Histological Pre- 

 parations, and New Method of Silver Impregnation.* — It is well 

 known, says F. W. Schmidt, that formalin over-hardens, and that con- 

 sequently preparations become unsuitable for further examination. 

 Noticing that formalin did not harden silver-gelatin emulsions though 

 gelatin alone was rendered very hard, the author ascribed this effect to 

 the action of the silver salts ; and working on the basis that animal tissues 

 might behave as gelatin does, he set about experimenting. He immersed 

 Alburnus bipunctatus in formalin until it was as hard as a board, and 

 afterwards in 1 p.c. silver nitrate solution. In about 14 days the brittle- 

 ness was removed. Larger objects, such as Gadus aeglefinus L., required 

 a little longer. Of course the objects were stained by the silver, and 

 especially in certain parts. The author then turned his attention to the 

 preventing of this staining, and also to ascertain if any substance would 

 also remove the brittleness. He found that a 1 : 10 solution of citric 

 acid would render the formalin-fixed specimens pliable, but as this was 

 expensive he used h p.c. nitric acid. Reverting to his observation that 

 the silver nitrate stained the objects, he goes on to show that formalin- 

 silver nitrate preparations are available not only for macro-, but for 

 microscopical examination, and gives the following procedure : — 

 (1) hardening in 10 p.c. formalin ; (2) immersion in 10 p.c. citric acid 

 for 14 days ; (3) immersion in 1 p.c. silver nitrate solution for 8 to 14 

 days. The method is stated to be specially useful for the nervous 

 system. 



* Anat. Anzeig., xxxvi. (1910) pp. G52-4. 



