EXPLANATION OF FIGURES. 



All the figxires have been drawn with Zeiss apoehromatic objective 1.5 mm. romponsating ocular and camera 

 lucida giving a magnification of 1 ,500 diameters. The figures have not been reduced in reproduction. In all of them 

 unaltered cells are representeil side by side with chromophile cells ju.st as they occur in the preparations. 



Figures 1 to 6 represent cells in the cerebral cortex of a male white mnu.se, 20 days old and weighins •"> grams. 

 The brain was cut into serial sections 4 /j in thickness and stained with fuchsin iind methyl green. All the figures were 

 drawn from cells in the .same section to insure uniformity in the action of the stain and of the difTerentiator. The 

 mitochondria are stained red, the Nis.sl .substance green, and the canalicular apjiaratus persists, in some of the cells, 

 in the form of clear, uncolorcd spaces. 



Figures 7 to 9 represent cells from the cerebral cortex of a male white mouse, 29 days old and weighing 10 grams. 

 Portions of the brain were prepared by the uranium-nitrate method of Cajal and were cut into serial sections 4 >i thick. 

 These figures were also drawn from a single section to insure uniformity in the action of the counterstain, methyl 

 green. The canalicular a|))iaratus is in the form of a blackened network and the \is.sl subst.ance is colored green. 



Fi<:. 1. Two cells, having a distinct increase in amount and intensity of the .stuining of the mitochondria. This change 

 may mark the first stages in the assumption of the chroniophilic condition. 



2. A nuich greater increase in amount of mitochondria and a slight increase in intensity of the staining of the Nissl 



substance and the nucleus. 



3. The Nissl sub.stance is more abundant. It is diffuse and stains more brightly. The outlines of the mito- 



chondria are indistinct. The nucleus stains darkly. \ few clear canals are visible near it. There is 

 what appears to be a shrinkage space on either side of the cell. 



1. .'^till greater clianges. The mitochondria appear to be going into .solution; outlines of nucleus barely dis- 

 tinguishable. 



5. The mitochondria have almost all gone into .solution. The Xi.ssl substance is almost entirely obscured by 

 the cloud of mitochondrial material which stains with the mo.st energetic of the two dyes, acid fuchsin. 

 The nucleus is invisible. 



t>. A complete "chondriolysis" or .solution of the mitochondria. The canalicular ajjparatus is present in the 

 vicinity of the nucleus. 



7. The increase in amount of the Nissl substance indicates a slight degree of ehromophilia. The canaUcular appa- 



ratus is blackened and shows no changes. 



8. Greater increase in the Nissl substance. It is diffuse, with marked hyperchromatism. The nucleus stains 



diffusely with methyl green. Its outlines are obscure. The canalicular apparatus, in black, is unaltered 

 and the cell as ;i whole is shrunken. 



9. Cell so intensely stained with the methyl green that the nucle\is can not be seen. Canalicular apparatus 



slightly condensed, othenvise unchanged. There is a considerable shrinkage of the cell. 



