AXIS-CYLINDER AND DENDIUTE STAINS. 429 



GUDDEN (N enrol. Centralb., xx, 1901, p. 152) takes the lactate of silver 

 (sold as " actol ") and finds it much more penetrating. 

 FAJERSTAJN (ibid., p. 98) uses ammonio-nitrate in a complicated way. 



820. Avoidance of Precipitates. G-OLGI'S process frequently 

 gives rise to the formation at the surface of the preparations 

 of voluminous precipitates that are destructive of the clear- 

 ness of the images. SEHRWALD (Zeit. wiss. Mik., vi, 1889, 

 p. 456) has found that this can be avoided as follows. A 

 10 per cent, solution of gelatin in water is made. The tissues 

 are coated with this, by dipping and cooling several times, 

 or are imbedded in it, in a paper imbedding box, with the 

 aid of a little heat, and are brought therein into the silver- 

 bath. After the silvering the gelatin is removed before 

 cutting by warm water saturated with chromate of silver. 



MARTINOTTJ wraps the tissue simply in blotting-paper, but 

 this does not appear to be efficacious. 



ATHIAS takes wafer-papers. 



RAMON Y CAJAL covers tissues with a layer of congealed 

 blood, which need not be removed before cutting, or with 

 collodion, or peritoneal membrane. See Retina. 



Modifications concerning the Preservation of the Preparations. 



821. Cutting. The chief quality of GOLGI'S process is that 

 it admits of the following of nerve-cell processes for a very 

 great distance. Evidently this cannot be done with very 

 thin sections. And as sufficiently thin ones can be obtained 

 without imbedding, the general practice is simply to wash 

 the preparations taken from the silver-bath with water, fix 

 them to a cork with gum, put the whole into alcohol for a 

 few minutes to harden the gum, and cut with a microtome 

 without imbedding. 



But imbedding is possible, if it can be got through rapidly 

 enough. Pieces of tissue as small as possible should be 

 dehydrated in from half an hour to two hours, put for the 

 same time into thin celloidin, then coated with thick 

 celloidin, gummed on a cork and cut, the sections being* 

 collodionised if necessary. Thin specimens such as retina 

 may be soaked for a short time in celloidin, put between two 

 slabs of solid celloidin lightly pressed together, and the 

 whole cut after a short treatment with alcohol of 70 per 

 cent. Similarly with paraffin. The tissues should be got 



