248 PEESEEVATION MEDIA. 



413. SQUIRE'S Glycerin Jelly (SQUIRE'S Methods and 

 Formulae, &c., p. 84) . Soak 100 grms. of French gelatin in 

 chloroform water, drain when soft, and dissolve with heat in 

 750 grms. of glycerin. Add 400 grms. of chloroform water 

 with which has been incorporated about 50 grms. of fresh egg- 

 albumen ; mix thoroughly, and heat to boiling-point for about 

 five minutes. Make up the total weight to 1550 grms. with 

 chloroform water. Filter in a warm chamber. 



414. Stephenson's Biniodide of Mercury and Iodide of Potas- 

 sium (Journ. Roy. Hie. Soc., 1882, p. 167). Interesting as giving a solu- 

 tion which when saturated has an index of 1'680, the highest index of any 

 known aqueous fluid. I have experimented both with strong and weak 

 solutions, and doubt whether much practical advantage can be derived from 

 them. Tissues are well preserved, but the preparations are ruined by a 

 precipitate which forms in the fluid. 



415. Monobromide of Naphthalin. See Journ. Roy. Mic. Soc., 1880, 

 p. 1043 (ABBE and VAN HEUECK), and Zool. Anz., 1882, p. 555 (MAX 

 FLESCH). 



416. THOMPSON'S High Refractive Medium, See Journ. Roy. 

 Mic. Soc., 1892, p. 902. 



Resinous Media. 



417. Resins and Balsams. Resins and balsams consist of a 

 vitreous or amorphous substance held in solution by an essen- 

 tial oil. By distillation or drying in the air they lose the 

 essential oil and pass into the solid state. It is these solidified 

 resins that should, in my opinion (and that, I believe, of the 

 best microscopists), be employed for microscopical purposes ; 

 for the raw resins always contain a certain proportion of 

 water, which makes it difficult to obtain a clear solution with 

 the usual menstrua, is injurious to the optical properties of 

 the medium and to its preservative qualities, and, further, 

 especially hurtful "to the preservation 6f stains. I therefore 

 recommend that all solution^ be fnade by heating gently the 

 balsam or resin in' a stove uritil it becomes brittle when cold, 

 and then dissolving in an appropriate menstruum. 



FOL (Lehrb., pp. 1389) is of a different opinion. 



Solutions made with volatile menstrua, such as xylol and 

 chloroform, set rapidly, but become rapidly brittle. Solutions 

 made with non- volatile -media, such as turpentine, set much 

 less rapidly, and pass much less rapidly into the brittle state. 



