INVERTEBKATA, CRYPTOGAMIA, MICROSCOPY, ETC. 615 



quantity of alcohol for twenty-four hours, and at the end of that time 

 be laid open, and the retina be then examined in glycerine, the optic 

 nerve fibres and ganglion cells will be found more or less well 

 preserved. But it is a matter of no small importance to regulate the 

 strength of the alcohol, and diluted alcohol will be found more useful 

 than strong alcohol. A mixture of equal parts of methylated alcohol 

 and water is a strength that he used for some time, with such excel- 

 lent results that he adhered to it during most of the time that he was 

 engaged in examining this part of the retina ; but latterly he found 

 that, in most respects, a weaker strength secured as good preparations, 

 and for some purposes produced better ones. For the preservation of 

 ihe processes of the ganglion cells, mixtures of one part of methylated 

 alcohol with two of water, and of one of methylated alcohol with three 

 of water, are peculiarly well adapted. The fibres of the optic nerve 

 expansion are well seen, whichever of these strengths is used. They 

 may be isolated in great numbers, and for great lengths, after the 

 bulb has been in equal parts of water and alcohol. When only a 

 fourth strength of alcohol was employed, the nerve fibres were, unless 

 well teased out, slightly obscured by adherent granules — probably 

 the remains of connective substance of the layer. 



"When the strengths of a third and a fourth were used, the bulb 

 was allowed to remain in the fluid for thirty-six or forty-eight 

 hours. 



Although both the ganglion cells and the nerve fibres in eyes, 

 treated by the above methods, can be examined at once in glycerine, 

 it may be found advantageous to subject the retina to other processes, 

 through which the hardened nerve elements can now pass without 

 injury. It may be placed first in water for a short time, and then 

 may remain overnight in staining fluids, and finally be examined and 

 preserved in glycerine, or, after being stained, it may be passed 

 through alcohol and oil of cloves, and preserved in dammar varnish. 

 The glycerine preparations show both the fibres of the optic nerve 

 expansion and the ganglion cells. The dammar preparations are 

 useful as permanent specimens of the nerve fibres. In either case 

 some careful manipulation with needles is necessary to disentangle 

 the nerve fibres, a process which is particularly troublesome in the 

 dammar prejiarations. Of all the staining fluids tried, a solution in 

 water of aniline blue was found to be by far the best. For the nerve 

 fibres aniline blue alone is sufficient ; for the ganglion cells a double 

 staining with aniline blue and eosin is useful. 



Eyes which have been placed in alcohol, as above directed, may 

 be preserved for a long period in glycerine without the nerve fibres 

 or ganglion cells sufi"eriug in the least. The effect of the glycerine 

 by its affinity for water is to produce a complete collapse of the eye- 

 ball. The lens preserving the shape of the anterior part of the bulb, 

 the posterior half is doubled up into the anterior half, forming a 

 cavity at the bottom of which is the stump of the optic nerve. It is 

 thus possible to prepare eyes at any time, and keep them ready for 

 examination. He had excellent preparations of the optic nerve fibres 

 and ganglion cells from the eye of a kitten, which, after being twenty- 



