Anatomy. — "/.? the post-emhryonal growth oj the nervous system 

 due onJy to an increase in size or also to an increase in 

 number of the neurones f" By Erik Agduhh. (Communicated 

 by Prof. J. Boeke). 



(Communicated in the meeting of Dec. 28, 1918). 



hitroduction. 



While investigating the effect of training on tiie post-embryonal 

 development of the nervous system ') I was confronted with the 

 following problem. Is tlieie generally an increase in the number of 

 axons during the post-embryonal growth of the nervous system ? We 

 are concerned with the roots of the spinal nerves. In the dorsal and 

 ventral roots of the spinal nerves there is, as is shown in more 

 detail below, no 7- and )"-(iivision of the nerve fibi-es. The problem 

 is thus practically' identical with another, viz. : is there an increase 

 in the number of neurones during the post-embryonal development? 



Up to the present time the condition of this question has been 

 such that the possibility referred to has been regarded as almost 

 excluded. This was due to the supposition that the nerve-cells were 

 small bodies so much differentiated that divisions in them could not 

 be imagined. Figures of division of cells in the central nervous 

 system of animals only a few days old have, however, been described, 

 although very eminent investigators, such as Marinksco, Prenant, 

 Vat'enza, etc. deny that these figures have anything to do with the 

 nerve elements, but consider them to be stroma elements. During 

 recent years the literature points to some extent in the direction of 

 the possibility of a post-embryonal new formation of neurones taking 

 place — although the newly-formed neurones are only considered 

 as replacing those that have been destroyed by degeneration. 



The results of the investigation undertaken by me with regard 

 to training (exercising) were of such a nature as to be difïicult of 

 explanation in the absence of a real increase in the number of 

 neurones during the post-embryonal growth of the animal. I was 



1) So far only a preliminary communication has been pubhshed: Der Einfluss 

 der Trainieren auf das morphologische Bild des motorischen Nervensystems 

 Hygica 1917 (LXXIX). 



