ZOOLOGY AND BOTANY, MICROSCOPY, KTC. 505 



and then filtered through filter-paper, the temperature of the fluid being 

 kept at about 50° 0. This takes from one to three days. 



At the present price of glycerin and formaldehyde, 1 litre of this 

 medium costs 3s. M. This medium is absolutely transparent, and when 

 set does not melt at the highest suunner temperature. 



This arsenious acidglycerin-gelatin (or shortly, "arsenious jelly ") 

 does not act as an ordinary mounting medium only, iDut has the property 

 of preserving colour better than the potassium-acetate-glycerin fluid or 

 other preserving fluids used in the Kaiserling and allied methods. It 

 can be used to mount specimens in jars, but the chief object in devising 

 this solid medium was to find a method by which specimens, and more 

 especially flat sections, could be fixed to glass plates so as to do away 

 with the distortion produced by the uneven walls of museum jars. The 

 use of glass plates has also the great advantage of diminishing cost and 

 reducing the space occupied by specimens. 



Mounting of Specimens on Glass Plates.* — For many years the 

 method which S. Delepine used consisted in mounting sections, or parts 

 of organs, not exceeding a quarter to half an inch in thickness, in 

 arsenious acid glycerin between two glass plates, a paper or a glass border 

 being used during mounting to hold the jelly. The excess of gelatin 

 having been removed, the edges were covered with adhesive india-rubber 

 plaster, over which a continuous layer of lead foil was glued. The pre- 

 paration was then finished by gluing a cloth band over the lead foil, or 

 by mounting in a wooden frame. 



Very thin sections mounted in this way are very permanent. Some 

 in the author's collection were over twenty-five years old, but thick 

 sections are frequently a source of trouble after a few years, owing to the 

 contraction of the gelatin and the penetration of air under the glass. To 

 avoid this difficulty, the idea of enclosing the specimen and medium in 

 an air-tight space between fixed plates was abandoned. The author now 

 mounts the specimen against the glass plate through which it is to be 

 seen. It is embedded in jelly, which is covered at the back with a 

 second glass plate smaller than the front plate. The back plate is also 

 used to apply a backing of suitable colour, generally white, grey, or 

 black. In the case of thick sections, whole organs, animals, etc., nothing 

 is done to close the sides, which are protected by resting the front 

 plate upon the rim of a box made of plaster of Paris, glass, or metal. 



The little glycerin which oozes out of the medium is absorbed by 

 some porous paper, plaster of Paris, or felt, which is placed between the 

 back plate and the bottom of the box ; this padding also supports the 

 back plate. Under these conditions the back plate follows the gelatin 

 when it shrinks, and air does not penetrate under the glass. Specimens 

 of almost any size can be prepared by this method. As to stability, the 

 author had specimens mounted seventeen years ago which were still 

 perfect, and had retained their colour without any appreciable change. 

 They had been exposed to fight for long periods. 



To facilitate manipulations and reduce the amount of time needed 



t Museums Journal, xiii. (1914) pp. 327-9 (1 fig.). 



