1893.] MICKOSCOPICAL JOURNAL. 55 



preparation, for the time necessarily required for the action of the 

 various reagents on a single specimen can be profitably employed 

 in transferring other preparations. The cover-glasses can be 

 handled very quickly, neatly, and witli perfect safety with a pair 

 of fine forceps. — Proc. A. S. AI. 



MICROSCOPICAL MANIPULATION. 



To Find the Refractive Index of Various Mounting 

 Media. — E. M. Nelson has given the following to the Quekett 

 Club : 



Provide two precisely similar equi-convex lenses whose iden- 

 tical refractive index, w, and radii, r, are known, and cement 

 them together with the mounting medium, whose refractive index 

 has to be determined. Now measure F., the principal focus of 

 the combination, then the refractive index of the mounting 

 medium. 



in = zjii — I — (r -:- zF). 



It is convenient to make the radii of the lenses 3 inches. Then, 



in = zm — I — (i-:-^). 



For example, let the refractive index in = i^ ; suppose the 

 combination to have no focus (like a piece of plane glass), then 

 F = <y: , and i -i- F= o. Therefore 



in' = 2in — 1^2. 



Let F= -\- 2 and we shall have the following result, which is 

 the same as that of the equi-convex lenses : 



in' = iin — 12=" ^\- 

 If the principal focus of the combination F is negative the 

 sign before the fraction changes. Let F == — 2 ; then 



111 = 2in — I — (i —. 2) ^2^. 



This method gives a great range of readings for indices vary- 

 ing between 2 and 2^. 



Heidenhain's Modified Micro -technical Methods. — 

 Prof. A. Ohlmacher {Medical Nezvs) describes Heidenhain's 

 method of preparing animal tissue for study. The process con- 

 sists in fixing in corrosive sublimate, dehydrating in alcohol, 

 clearing in bergamot oil, and imbedding in paraffin. 



The fixing solution is made by saturating a \ per cent, solution 

 of common salt in distilled water, with corrosive sublimate. The 

 solution should be supersaturated with sublimate. Cubes of tissue, 

 three-eighths of an inch on the edge, are dropped in some of this so- 

 lution. A half-hour to an hour's immersion is sufficient for perfect 

 fixation. The object is then brought directly into 95 per cent, alco- 



