CHAPTER XXXI V. 467 



10 per cent, gelatin, and, as soon as this has set, they are put into 

 the silver bath, keeping the latter in some dark place. It appears 

 that surrounding a tissue with gelatin makes the impregnation 

 slower, and for this reason Mann allows a day longer for the silver 

 bath. 



MARTINOTTI (op. cit.) covers pieces with a layer of a pap of filter 

 paper and distilled water. 



ATHIAS wraps tissues in wafer papers. 



RAMON Y CAJAL covers them with a layer of congealed blood, 

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

 peritoneal membrane. See " Retina." 



Modifications concerning the Preservation of the Preparations. 



892. Cutting. As pointed out in 880, one of the chief qualities 

 of Golgi's method consists in allowing one to follow nerve-cell 

 processes for a great distance. Evidently this cannot be done with 

 very thin sections ; and as sufficiently thin ones can be obtained 

 without embedding, the general practice is simply to wash the pieces 

 taken from the silver-bath with distilled water, fix them with gum 

 to a cork or wooden cube, put the whole into alcohol for a little 

 while to harden the gum, and cut by means of a sliding microtome 

 without embedding. 



But quick embedding, particularly in celloidin, is quite possible, 

 and should be resorted to for material either brittle or otherwise 

 difficult to cut. Pieces of tissue as small as possible are brought 

 in the course of about two hours through the ascending series of 

 alcohols into absolute alcohol ; after having changed this a couple 

 of times, pieces are transferred for another one or two hours in thin 

 celloidin, then coated with thick celloidin, and by means of this 

 fixed to a wooden cube, the celloidin being a little hardened by 

 means of chloroform vapour, as usual. The whole is left for a little 

 while in 70 per cent, alcohol, and sections made in the usual way. 

 If these operations are started in the morning, when going into the 

 laboratory, pieces are ready for cutting at about 2 p.m., sufficient 

 time remaining for the further treatment of the sections according 

 to the directions given above ( 881). Care should be taken, of 

 course, not to transfer the sections into absolute alcohol if it is not 

 considered safe to dissolve the celloidin. In this case dehydration 

 can be carried out as usual up to 98 per cent, alcohol, and the 

 sections transferred into fluid absolute guaiacol and cedar-wood oil 

 as already described in 881. 



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