626 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. [20] 



these in order to be completely dehydrated must be transferred succes- 

 sively to two baths of absolute alcohol. 



This method of staining sections of the nervous system is said to give 

 results much superior to carmine, the anilines, or gold chloride, and to 

 differentiate the fibers of the gray matter better than any other dye. 



Embedding in celloidin. — Whitman, in the American Naturalist for 

 October, 1883, describes the method as follows: "Very elegant results 

 may also be obteined by an embedding mass originally invented by 

 Duval and recently much improved by Merkel and Schiefferdecker.* 

 This is collodion, or, j^referably, a solution of so-called celloidin. If this 

 substance cannot in general be cut to such extreme delicacy as the al- 

 buminous mass just described, it has a great advantage in being ex- 

 tremely pellucid. The original communication of the last-named author 

 is easily accessible, so that Professor Thoma considers it superfluous to 

 give a detailed accoimt of it, but adds a few remarks on his own expe- 

 rience with it. 



"According to the formula of Schiefierdecker, the embedding fluid 

 consists of concentrated solution of celloidin in a mixture of equal parts 

 of absolute alcohol and ether. The specimen is soaked successively in 

 absolute alcohol and ether, and in the embedding fluid. This requires 

 at least several days. After this time the embedding proper may be 

 undertaken, and for this we have the choice of two methods. 



"The even surface of a cork is covered with a thick solution of cel- 

 loidin, so as to form by evaporation a strong collodion membrane on the 

 cork. Upon this is put the specimen, covered layer by layer with fresh 

 quantities of the solution of celloidin, each being allowed to dry only par- 

 tially. When the object is thoroughly covered we immerse it in alcohol 

 of 0.842 specific gravity. In twenty-four hours the whole is ready for 

 cutting. 



"The other method makes use of little paper boxes for the embedding. 

 The specimen soaked in celloidin solution is fixed in the box by pins, 

 the box filled with celloidin. The preparation is then placed on a flat 

 piece of glass and covered with a glass cover which does not exactly fit 

 the glass plate. In a few days the ether will have evaporated gently 

 and slowly from the embedding mass, and the latter will shrink a little. 

 If necessary more celloidin solution can be poured into the paper box to 

 fill it again. It is only necessary to moisten the surface of the first mass 

 with a drop of eth^r in order to allow of a perfect junction between the 

 old and the new layers. The preparation is again exposed to slow 

 evaporation below the glass cover, and a few days later the embedding 

 mass will be consolidated to an opaline body, whose consistency can 

 well be compared to that of the albumen of a boiled egg. The walls of 

 the paper box can now be removed, and the embedding mass placed in 

 very dilute alcohol, which will, in a very few days, produce a proper 

 degree of consistency to admit of cutting. 



*Arch. f. Anat, u. Physiol. (Anat. Abthiel.) 1882. 



