ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 875 



thus treated are obtained excellent images of the finer parts of the 

 retina, especially from the layers of the rods and cones. 



The author recommends hardening and staining the retina in situ, 

 i.e. while still associated with the sclerotic and choroid, with a 0-3 

 to 1 per cent, hyperosmic acid or • 2 per cent, chromic acid solution. 

 For the latter he uses alum carmine and picrocarmine. Very fine 

 staining was obtained by means of iron and vanadium chloride in 

 combination with 2 per cent, tannic or gallic acids. By these re- 

 agents the rods and canes, the internal granular layer, and the nuclei 

 of the ganglion cells took on a deep blue to a black colour ; while the 

 rest of the constituents of the retina remain unstained. They bore 

 after-staining with anilins, especially acid fuchsin, well. 



In cutting the retina, the chief difficulty is to obtain sections 

 which have a perfectly flat surface throughout, and which on their 

 whole extent show the same retinal layers. The cause of this difficulty 

 lies in the spheroidal form of the retina itself, and secondly, in the 

 faulty placing of the preparation in the microtome. Krause tried to 

 do away with this inconvenience by imbedding pieces of the retina in 

 the object-carrier itself, by means of paraffin, a piece, of cork, and 

 some tin-foil. A disc of paraffin, to which the proper consistence 

 had been given by mixing some vaseline with it, was fixed to the cork, 

 and this latter fastened on the carrier. The tin-foil was apparently 

 used merely for the purpose of keeping the retina straight. By this 

 means Krause obtained perfectly flat sections. 



Preparation of the Eye for Histological Examination.* — Mr. 

 J. W. Barrett thinks that sections of the entire eye can only be pre- 

 pared with the aid of imbedding and infiltrating materials ; if celloidin 

 is to be used the eye should be opened by a short incision through 

 the sclerotic, and should be placed in Miiller's fluid and chromic acid 

 solution, or better 2^ per cent, watery solution of carbolic acid if a 

 section of the lens is desired. After alcohol of various strengths it 

 should be stained with alcoholic borax carmine (formula : carmine, 

 (No. 40) gr. xv. ; borax, 1 dram ; water to 8 oz. ; dissolve by warming, 

 and slowly evaporate to 4 oz. Add 7 oz. of alcohol). After washing 

 it should be transferred to alcohol and then to an equal mixture 

 of alcohol and ether. After twenty-four hours it should be transferred 

 to a thin solution of celloidin in equal parts of alcohol and ether. 

 In two or three days the celloidin will have penetrated, and the eye 

 may be now imbedded. 



This should be done in a box with a perfectly flat floor, and the 

 eye covered with a tolerably thick solution of celloidin. Put under 

 a bell-jar, the alcohol and ether will diffuse and the celloidin slowly 

 consolidate ; the bell-jar must be lifted from time to time. The time 

 necessarily varies from one to six days. If the whole mass is too large 

 for sections, it may be cut into slices about a quarter of an in h thick. 

 Directions for cutting are added. Sections of parts of the eye, 

 without the lens, of young or of embryonic eyes may be readily 

 obtained by infiltrating and imbedding in paraffin by the chloroform 

 process. 



* Quart. Jourii. Micr. Sci , xxvi. (188(5) pp. 607-21. 



