1033 



system. Among the investigators who have made such observations 

 we mention Rktzius, v. Gkhuchten, Rainion y Ca.jai,, Dkjkkink. 



The presence of degenerating nerve elements in individnals that 

 are growing also renders the possibility of a regeneration of sncli 

 vei'y probable. If there is no regeneration, the nerve elements would, 

 of course, decrease during growth — a phenomenon thai is not indi- 

 cated by any recorded observations. The probability of generation 

 becomes certainty, however, when one investigates snitable prepa- 

 rations from the central nervous system, for instance from the 

 spinal cord of animals at various post-embryonic ages. Such prepa- 

 rations show numerous figui-es of new growth, which seem to me 

 sutHicient to explain not only how degenerated ganglion cells 

 are replaced, but also how the increase in nerve fibres in the 

 central roots arises, which I pioved above to exist during the pei-iod 

 of growth. 



I have made suitable preparations for these investigations from 

 the spinal cord of toads, mice, rats and dogs of ditïerenl post-em- 

 bryonic ages. The uiaterial was fixed either in Flemming's or Zenker's 

 fixing liquids and the paraffin sections cut from it were impregnated 

 either with Heidenhain's iron-alum h(jematoxylin or with Eri>ich's 

 acid iKBmatoxylin. I have in addition, quite excellent Bielschowsky- 

 prepai-ations from this material. 



In the hcKmatoxylin-impregnated preparations from toads 2 cm. 

 long (from neck to sacrum) and ten days old mice 1 found some 

 — but very few — mitoses. On the other hand I have not found 

 any certain examples of such mitoses in the older individnals of this 

 species nor in six and seventeen days old dogs or in full-grown 

 ones. In a young mouse 23 days old (Mils muse. var. <ilbas) I found 

 three appearances, which are reproduced in figs. 9 and 11. The 

 figures are carefully drawn from preparations — which are from 

 the material that was fixed by Fi.emming's method — and, at the 

 first glance, certainly produce the impression of being mitoses, and 

 it is possible, of course, that this is the case. A nundier of facts 

 seem to me, however, to render this doubtful; these are first, that I 

 have not found any more mitoses in this animal and, secondly, that in 

 other mice of equal age, in which the material was fixed according to 

 Zenker's method — this method gave better and finer results — 

 and impregnated in the same way, I have not found any trace of 

 mitoses. In any case I have not found any appearance of a mitosis in pre- 

 [)arations of the spinal cord of white mice more than 24 days old. 

 My observations of mitoses in the spinal cord of growing individuals 

 thus agree on the whole with those previously made by other in- 



67* 



