AND DENDBJTES 509 



is removed, before cutting, by means of warm water saturated 

 with silver chromate. Mann {Physiol. Ilistol., 1902, p. 276) 

 finds that the method gives good results provided the gelatin is 

 not rendered insoluble by the action of light. To prevent this 

 he proceeds thus : Either in the photographic dark room or 

 in the evening, by artificial light, tissues, tied loosely to a thread, 

 are immersed three times into liquefied 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 



1039. Cutting. As pointed out in § 1026, 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 imbedding, 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 imbedding. 



But quick imbedding, 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 to 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 (§ 1027). 

 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 



