NERVOUS SYSTEM— GENERAL METHODS 463 



mate solution. One should have recourse to it only for special 

 cytological methods, taking care not to use parafTin of too high 

 a melting point. Shrinkage is reduced to a mininmm if the 

 tissues are treated with Zenker's fluid for a few hours before 

 being dehydrated. 



Imbedding in celloidin is very largely used, and to great advan- 

 tage for many purposes. 



If, notwithstanding every precaution, the celloidin has not 

 thoroughly penetrated the tissues, good sections may still be 

 obtained by Duval's method of collodionising the sections. 

 The cut surface of the block is dried by blowing on it, and is 

 covered with a thin layer of collodion laid on it with a brush. 

 As soon as this layer has somewhat dried, which happens very 

 rapidly, a section is cut, and the cut surface collodionised as 

 before, and so on for each section. 



The above applies to section cutting of small, medium-sized 

 and even relatively large pieces. Also unusually large pieces, 

 entire human hemispheres, and brains of high vertebrates can 

 be cut into relatively thin and, if necessary, serial sections after 

 imbedding either in celloidin or paraffin or by mixed methods. 

 The processes used for the purpose do not differ essentially from 

 those above-mentioned and fully described in Chapters IX 

 and X, but (particularly for cyto-architectural and fibre- 

 architectural studies) special apparatus and installations are 

 needed, the description of which is outside the province of 

 this book. 



See also Ciaglinski, Ztschr. wiss. Mikr., viii, 1891, p. 19 ; Feist, 

 Ztschr. wiss. Mikr., viii, 1891, p. 492 ; Defecke, op. cit. ; De.ierine, 

 Anat. Centres Nerveux, i, 1895, pp. 1-57 ; Strasser, Ztschr. tviss. Mikr., 

 ix, 1892, p. 1 ; Brodmann, Journ. Psychol, ti. Neurol., ii, 1903-4, 

 p. 206 ; Warnke, ibid., p. 221 ; Liesegang, Ztschr. iviss. Mikr., xxvii. 

 1910, p. 369 ; Venderovic, Anat. Anz., xxxix, 1911, p. 414. 



989. Numbering in Series Sections from Celloidin Blocks. 



Besides the methods described in §§ 216 et seq., the following one 

 by Da Fano (Proc. Physiol. Soc, Journ. Physiol., Ix, 1925, p. 13) 

 has been found extremely useful whenever the sections can be 

 mounted without dissolving the celloidin. Pieces of any desirable 

 size are imbedded in celloidin by means of paper boxes or any 

 similar device which may allow one to arrange them according 

 to the way in which the series will have, afterwards, to progress. 

 At the same time care should be taken that the pieces are sur- 

 rounded by an amount of celloidin sufficient for subsequently 

 writing a progressive number on the sections. The celloidin 

 blocks are stuck to appropriate supports, and these are fixed on 

 the microtome as usual. As each section is cut it is spread flat 

 on the knife and the free celloidin at one corner dried with 

 blotting paper. Without any loss of time a number is written 



