ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 305 



the staining fluids generally used, and therefore becomes very visible 

 in the preparations. The latter inconvenience should in all cases 

 be avoided by colouring the specimen in toto before imbedding. For 

 this purpose the fluids of Grenacher,* and especially alum-carmine, 

 may be recommended. The imbedding mass remains nearly abso- 

 lutely colourless if the specimen, after staining and before imbedding, 

 is hardened again in alcohol. 



Very elegant results may also be obtained by an imbedding mass 

 originally invented by Duval, and recently much improved by Merkel 

 and Schiefferdecker.f This is collodion, or, preferably, a solution 

 of so-called celloidin. If this substance cannot in general be cut 

 to such extreme delicacy as the albuminous mass just described, it 

 has a great advantage in being extremely pellucid. The original 

 communication of the last-named author is easily accessible, so that 

 Prof. Thoma considers it is superfluous to give a detailed account of 

 it, but adds a few remarks on his own experiences with it. 



According to the formula of Schiefferdecker, the imbedding fluid 

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

 parts of absolute alcohol and ether. The specimen is soaked succes- 

 sively in absolute alcohol and ether, and in the imbedding fluid. This 

 requires at least several days. After this time the imbedding 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 

 celloidin, 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 partially. When the object is thoroughly covered, we 

 immerse it in alcohol of • 842 sp. gr. In twenty-four hours the whole 

 is ready for cutting. 



The other method makes use of little paper boxes for the imbed- 

 ding. The specimen, soaked in celloidin solution, is fixed in the box 

 by pins, and 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 imbedding mass, and the 

 latter will shrink a little. If necessary, further celloidin solution can 

 be poured in the paper box, to fill it again. It is only necessary to 

 moisten the surface of the first mass with a drop of ether, 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 imbedding 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 imbedding mass placed in very dilute alcohol, which 

 will in a few days produce a proper degree of consistency to admit of 

 cutting. 



This method difiers in some degree from that which Schiefferdecker 

 gives for imbedding in paper boxes. As other observers have re- 



* Arch. f. Mikr. Anat., xvi. (1879) p. 465. 

 t Arch. f. Anat. u. Physiol.. (Anat. Abtheil.) 1882. 

 Ser. 2.— Vol. III. X 



