958 



probable, even a certain, waj of explaining this phenomenon, namely 

 that in both the spinal ganglia and the central nerve system there 

 are young cells which have not hitherto sent ont any axons, and 

 which have the power of dividing. (This point is discussed more 

 completely below). Such cells aie considerably more numerous in 

 young specimens than in older ones. I am thus of the opinion that 

 this part of the investigation has not given any support either to 

 an assumption of the possible occurrence of nerve-cells that send two 

 axons into the dorsal or ventral root. Nor have I found in the 

 literature any statement that points to this conclusion. It thus still 

 remains to investigate other possibilities. 



Do axons grow either from newly formed or from older nerve-cells 

 lying in reserve. 



This part of the investigation, which I tried to avoid as long as 

 possible, in the hope of tinding other explanations of the post- 

 embryonal increase in the axons, has, however, gradually become 

 the most central — the main part, on which the entire result is 

 based. Observations made here and there in the preceding parts of 

 the investigation indicated clearly that the solution to the problem 

 was to be sought in this direction. Such a solution, however, does 

 not quite agree with the hitherto prevailing view as to the develop- 

 ment of the nerve system and the character of the neurones. There 

 is, however, as we shall see, an abundance of facts to support this 

 solution. 1 shall begin with an examination of the 



Spinal ganglion. 



Heidenhain, M. ') writes: "Es würde gewiss für die Physiologic 

 von grosser Bedeutung sein wenn wir behaupten könnten, dass wir 

 mit der Anatomie der cerebrospinalen Gangliën im reinen sind. Dies 

 ist jedoch nicht der Fall. Erstlich ist der Ursprung der erwahnten 

 atferenten sympalhischen Faserii leider nicht naher bekannt und 

 zweitens befindet sich nacli der Zahlung von Gaule und Lewis, 

 ebenso von BtJHLER, in den Gangliën eine ausserordentliche Ueber- 

 zahl von Zeilen deren Fortsatze wir noch nicht kennen". 



Among the many investigations concerned, among other things, 

 with the making of comparisons between the number of mednllated 

 nerve fibres in the dorsal root and the number of cells in the spinal 

 ganglion belonging to the root, the following may be cited: 



') Heidenhain, M. Plasma und Zelle. Jena 1911. 



