1893.] MICROSCOPICAL JOURNAL. 55 



preiiMiation. for tlic tinic ncccssai il\- required loi- the action ot'tlie 

 various reafjents on a single specimen can he proHtal)Iy employed 

 in transtcrrin<j other preparations. The cover-<^lasses can be 

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

 of fine forcejis. — Proc. A. S. M. 



MI( H()S((H»T(VVL MAMPl LATION 



To Find the Refractive Index of Various Mounting 

 Media. — I-I. AL Nelson has gi\cn the foUowinj.^ to the C^uekctt 

 Clul. : 



Provide two precisely similar cqui-convex lenses whose iden- 

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

 them together w'ith the niountino^ medium, whose refractive index 

 has to be determined. Now measure /*", the principal focus of 

 the combination, then the refractive index of the mounting 

 medium. 



lit = zii/ 1 (''' : 3/^) . 



It is convenient to make tlie ratlii of the lenses 2 inches. Then, 



ni = 2?n — I — ( I -^ J^) . 



For example, let the refractive index w^i^; suppose the 

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

 jp = cc , and i -.- JF =^ o. Therefore 



w' = 2w 1=2. 



Let /^= 4- 2 and we shall have the following result, whicli is 

 the same as that of the equi-convex lenses : 

 Jll = 3w — i^ = I^' 



If the principal focus of the combination I^ is negative the 

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

 m' = 2m — r — (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. ^V. Ohlmacher {Medical News) 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 iml)edding in paraflin. 



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 suiilimate. 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 percent, alco- 



