474 AXIS-CYLINDER AND DENDR1TE STAINS. 



sublimate not utilised by the reaction, and which still permeates the 

 tissues. As a matter of fact sections of pieces thus treated are very 

 easily cut and can be transferred from one to another fluid without 

 danger of injuring them. Moreover, they can be counterstained, 

 and the impregnation keeps sufficiently well, particularly if sections 

 are mounted without a cover-glass. But in such preparations, 

 sometimes quickly, sometimes slowly, opaque granules and minute 

 needle-like crystals become almost always developed. 



To avoid this I recently proposed (see DA FANO, Proc. Pliysiol. 

 Soc. Journ. PhysioL, liv, 1921) to treat sections much in the same 

 way as by the so-called process of toning and fixing Bielschowsky 

 preparations and the like. (See DA FANO, ibid., liii, 1920.) I 

 proceed thus : Pieces which, by a trial section, have been found 

 well impregnated, are washed for some hours in distilled water 

 and then brought, through many changes of alcohol of ascending 

 strengths, into absolute alcohol, and then embedded in celloidin in 

 the usual way. The celloidin blocks are hardened in 70 per cent, 

 alcohol, where they can be safely left for many days and weeks. 

 Sections of the desired thickness are collected in 60 per cent, alcohol, 

 transferred into distilled water and here thoroughly washed. They 

 are then treated for five to ten minutes with 5 per cent, ammonia 

 and washed over again in two or three changes of distilled water. 

 At this point toning is carried out by means of a slightly acidified 

 0-2 per cent, gold chloride solution, in which sections are left for 

 ten or fifteen or twenty minutes, according to their thickness. After 

 a quick washing in distilled water they are passed for three to five 

 minutes in 5 per cent, sodium hyposulphite and washed once more 

 in distilled water. From this they are transferred successively into 

 30, 50, and 70 per cent, alcohols, to each of which 1 drop of saturated 

 iodine tincture to every 5 c.c. of alcohol has been added. Sections 

 remain in each alcohol ten to fifteen minutes and are lastly transferred 

 into pure 70 per cent, alcohol. 



At this point the process is ended, and one can proceed to mount 

 the sections in the usual way, or re-transfer them into distilled water, 

 counterstain them lightly with a carmine solution, dehydrate with 

 alcohols of ascending .strength up to 95 per cent., pass them through 

 two changes of carbol-xylol and mount them under a thin cover- 

 glass in xylol-colophonium or balsam. If desirable and safe, the 

 celloidin can be removed before definite mounting by passing sections 

 through absolute alcohol, and alcohol-ether if necessary. 



The process is simpler than the rather complicated platinum 

 substitutions of ROBERTSON and MACDONALD (Journ. Ment. Sc., 



