J 032 



both glia and ganglion cells. The mitoses found in the central 

 nervous system of joang animals do not seem to refer to so-called 

 neuroblasts (His) '), b"f ^l^e preparation indicates that Kokli.iker ") 

 is right when, partly by reasoning and partly by direct observations, 

 he comes to the conclusion that those "Keimcellen" that are in 

 mitosis are undifferentiated epithelium-cells, which give rise to both 

 glia and ganglion cells. Schaper ') arrives at the same result by his 

 investigations of the course of differentiation in the central nervous 

 system of the trout. We thus seem to be justified in postulating as 

 a fact that as long as mitoses can be shown in the central 

 nervous system a new formation of ganglion cells is also taking place. 

 In Prenant ") we read as follows: a. "Les cellules nerveuses, en 

 se différenciant, out perdu le pouvoir de se reproduire, b. Les rares 

 multiplications qu'il a été possible d'observer dans les cas de cicatri- 

 sation de portions du névraxe, appartiennent a la nenroglie (Valknza, 

 Marinesco, Monti) ; c. Enfin il n'est [)as exclus que les quelques mitoses 

 observées doivent également être assignees a la neuroglie". Among 

 the investigators who do not seem lo be able to admit the possi- 

 bility of an increase of the neurones during post-embryonic life 1 

 want to njention also Bizzozero *) and Marinesco'). In deciding such 

 matter these authors seem more or less to have proceeded from the 

 idee préconcu that the neurons have a very long life and 

 are nearly perpetual. They consider that this is an absolutely neces- 

 sary qualification if the individual is to perserve its psychical 

 inheritance, to form associations of ideas, and for memory in general. 

 A close study of suitable preparations of, for instance, the spinal 

 cord from animals of different ages will soon convince us that 

 this does not quite agree with the real facts. For in these 

 preparations one finds not infrequently figures of ganglion cells 

 which are degenerating as well as those which indicate generation. 

 Nor is the literature on the subject without scattered statements 

 about observations of such degeneration in the central nervous 



1) His, Die Neuroblasten und deren Entstehung im embryonalen Mark. Arch f. 

 Anal. u. Entwickelungsgesch. 1889. 



2) V. KoELLiKER, Gewebelehre, Bd. 2, 1893. 



5) Schaper, Archiv, fur Enlw. mech. der Organ. Bd. 5. 



^) Prenant, Histologie et Anatomie microscopique, t. 11. p. 353, 1911, 



") BizzozERO, G . Accrescimento e rigenerazione neH'organismo (Conference du 

 Prof. G. BizzozERO au Congres international tenu a Rome en 1894). Voir, en 

 outre, dans le 2« volume des oeuvres scientifiques du même auteur publié a Milano 

 en 1905, et dans les Arch, ital de Biol. t. XXI, p. 93, quoted from Paladino. 



^) Marinesco, G., La cellule nerveuse, Vol. 1, p 400, Paris 1909. 



