THE STRUCTURE OF CHROMOPHILE CELLS OF THE NERVOUS SYSTEM. 31 



come off. Allow to cool. I.ct the stain remain on the sections for about (i minutes. Return tiie 

 stain to the bottle. 



(6) Dry off most of the stain with a towel and rinse in distilled water, so that the only stain 

 remaining is in the sections. If a large amount of the free stain remains it will form a troublesome 

 precipitate with the methyl green; on the other hand, if too much stain is removed the coloration of 

 the mitochondi'ia will be impaired. 



(7) Again dry the slide with a towel, except for the area covered by .sections. Allow a little 

 1 per cent methyl green, added with a pipette, to flow over the sections, holding the slide over a piece 

 of white paper so that the colors may be seen. Apply the methyl green for about .o seconds at first 

 and then modify the time to suit the needs of the ti.ssue. 



(8) Drain off excess of stain and plunge the slide into 9.") per cent alcohol for a second or twn, I lien 

 rinse in absolute for the same time, clear in toluol, and mount in balsam. 



Several difficulties may be met with: (1) The methyl green may remove all the fuchsin, even 

 when it is only a]ipli(>d for a short time. This is due to incomplete mordanting of the mitochondria 

 by the chrome salts in the fixative. It may often be avoitled, either by omitting the ti-eatment with 

 permanganate and oxalic acid, or by treating the sections with a 2 per cent solution of potassium 

 bichromate for a few minutes immediately before staining (as advised by Bensley). The action of 

 the permanganate and oxalic is to remove the excess of bichromate. (2) Or the fuchsin may stain 

 so intensely that the methyl green removes it very slowly or not at all. This, on the other hand, is 

 due to too much mordanting. It may be corrected by i)rolonging the action of the permanganate 

 and oxalic. (3) Sometimes, after obtaining a good differentiation, the methyl green is washed out 

 before the slide is placed in toluol. This may be avoided by omitting the 95 per cent alcohol, by 

 passing from the methyl green to the absolute direct. (4) Unfortunately the stain is not very perma- 

 nent. Under favoral)le conditions it will last for 3 or 4 .years. The fading in color is hastened by 

 light and by heat, and it proceeds very rapidly in a damp atmosphere. 



Cajal's (1912, p. 211) uranium-nitrate method was employed for the canaUcuhir 

 apparatus in its original form, except for the substitution of methyl green in tli(> 

 place of carmalum as a counterstain. 



Control ]ireparations were fixed in a variety of fluids and were .stainc^d in many 

 ways, as will ai^joear later. 



The figures have been made from specimens prepared by the ab()\e-iuentioncd 

 fuchsin-methyl green method, by which th(> mitochondria are stained red, the Nissl 

 substance green, while the canalicular api)aratus nmiains uncolored; and also from 

 specimens made by the uranium-nitrate method, which black(>ns the canalicular 

 apparatus and colors the Nissl substance green. 



OBSERVATIONS. 

 Chromophile cells, as the name implies, po.sse.ss an unusual affinity lor stains, 

 which may be either acid or basic. Their structure is variable. A glance at the 

 figures is sufficient to show this. The variations may represent stages in a i>rocess, 

 which, when i)tislK>d to an extreme, results in a cell in an advanced stage of chromo- 

 philia, but of this we have no conclusive proof. Neither can we assert that the 

 jn-ocess proceeds in this direction, for the changes observed may e<iually well be 

 interpreted as taking place in the reverse order. We do not yet know whether the 

 series is homogeneous; that to say, whether we are not arbitrarily groajjing se\'eral 

 ])rocesses of different nature tinder the same heading. For instance, a mitochondrial 

 increase (figures 1 and 2) may not precede a diffuse staining of the whole cell with 

 mitochondrial dyes (figure 6), which may be brought about in an entirely different 

 way. Nevertheless, the cells are all chromophile in the sense already defined, that 

 they stain deeply. 



