The division of differentiated cells in the central nervous system of the white rat

1 The aggregate weight of the 4 foetuser examined, wa5 3. 9 g. , each fnetur being about 17 mm. in length. Oullc acid 84, 4 rolr. Ale. 9, 3 r o l l. Chromic acid, % 3 rolr. JOURNAL OF COMPARATIVE NEUROLOGY. MING'S solution, the former giving the best results. It was imbedded in paraffin, and stained with iron-lack-haematoxylin, either alone or with erythrosin as a counter-stain, with saffranin and with toluidin blue and erythrosin. One series from the new-born rat was carried through by VIGNAL'S method ; i. e. alcohol-osmic acid hardening, picrocarminate of ammonia stain, -this method being said by VICNAL to demonstrate the character of the cytoplasm and processes unusually well. Unfortunately it does not stain the mitotic figures, so that it was not of much value for this study,. except that it showed with great clearness the different forms of glia cells. GRAF'S fluid and iron-lack-haematoxylin gave the most satisfactory results. The cord and cerebral. hemispheres of the new-born rat were first studied, and therefore the results obtained from them will be given first. The cord of the new-borrl rat contained a large number of mitoses, which were found chiefly in the outer layers ; the number on the ventricular surfaces was suprisingly small. In the brain the ventricular mitoses were more numerous than in the cord, but here also the extra-ventricular predominated. The brain and cord of the 24-hour rat contained fewer mitoses than the new-born rat, while in the three days and four days old specimens tlic number seemed equal to that of the new-born. Comparing the foetus with these older specimens, a striking difference was seen, for here the mitoses seemed to be predominantly on the ventricular surfacts. Figs. I, 2, 3, 4. In order to decide the question beyond doubt the mitotic figures were counted in 1 5 sections, 6%, 11 in thickness, taken from the cerebral hemispheres and from the cervical, thoracic and lumbar regions of the cord of the new-born rat. Also from the cerebral hemispheres and lumbar cords of the foetus and of the 24-hours and four day specimens. The sections of the hemispheres were coronal and taken at the level of the chiasma. The following tables give the results of these counts. HAMILTON, Division of CeZZs in Nemous