ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 101» 



poses white cement, is smeared round the margins of the slip except that 

 which corresponds with the border of the slide and a small portion of 

 the edge opposite. (2) Two slips, preferably square ones, are accu- 

 rately superposed, and then vaselin or cement smeared over the com- 

 bined rims except one, which is left free, and a part of the edge opposite. 



To use the slips or slides, touch with the free edge the drop of 

 Wood, and when the whole space has been slowly filled the unsmeared 

 portions of the margin are closed up with vaselin or cement. Stains 

 are best added by placing a drop on the surface and puncturing through 

 the drop. 



The advantages claimed for this method are that an extremely thin 

 and uniform film is secured ; that the slides or slips can be used by the 

 most unskilful ; and that when prepared beforehand a large number, 

 especially of paired slips, can be kept in a small space quite ready for 

 use. 



Formol as a Preservative and Fixative.* — K. Diederichs in some 

 noies on the u<?e of formalin, which is a 40 p.c. solution of gaseous 

 formaldehyde (CH 2 0) in water, alludes to its most important uses as a 

 fixative and preservative agent. For soft animals such as Mollusca and 

 even Medusae it is excelleut in the proportion of 1 part formalin to 

 20 or more parts of water. As a rule plants do not keep so well as 

 animal specimens, though for fruit and fungi it is suitable. While 

 formalin hardens animal objects it softens vegetables, but in the full 

 40 p.c. solution, plants can be hardened and thus rendered suitable for 

 microscopical technique. 



In combination with Muller's fluid 1-10 it forms an excellent 

 medium for hardening brain. For the lens 1-40 is sufficient. At the 

 present time it is extensively employed in bacteriological technique, many 

 stains being made up with it, so that the specimens are stained and fixed 

 simultaneously. It is of inestimable advantage for preserving cultures 

 so that they shall retain their characteristic appearauce at any given 

 stage. It is equally applicable to plate and tube cultures. 



Large anatomical preparations are preserved by immersing them 

 wrapped in cotton wool in a mixture of 200 ccm. formalin, 1000 ccm. 

 water, 15 grm. potassium nitrate, and 30 grm. potassium acetate for 

 24-48 hours. Alternative solutions are : (1) Formalin 100, acetate of 

 soda 30, chlorate of potash 5, distilled water 1000. (2) Water 1000, 

 formalin 750, nitrate of potash 10, and acetate of potash 30. (3) Forma- 

 lin 50, artificial Carlsbad salts 40, water 1000. After removal from 

 any of the foregoing the preparations are transferred to 60 p.c. alcohol 

 for 2 days, and then for similar periods to 80 p.c, 90 p.c, and 93 p.c. 

 alcohol. By this stage the colour is regenerated. The preparations are 

 next transferred to the preservative which consists of 290 parts glycerin, 

 100 parts acetate of potassium, 1000 parts water. Alternative solutions 

 are : (1) Water 90, glycerin 54, acetate of soda 27. (2) Water 1000, 

 nitrate of potash 2 * 5, saccharum 20, chlorate of soda 250. 



Formalin-gelatin has recently been applied to anatomical objects. 

 In 200 ccm. of water at 90°, 6-7 p.c. of gelatin is dissolved without 

 stirring. The supernatant thin opalescent layer is decanted off, filtered 



* Zcitschr. f. nngew. Mikr., vii. (1T01) pp. 14^-0. 



