1908. |] Minute Structure of the Nervous System. 437 
American histologist, who has shown by a series of clever and successful 
experiments on frog larve that the nerve-fibres grow out of the central organ. 
Harrison was, in fact, able to trace this process under the microscope in the 
living tissue and could even determine how much the fibres grow in a minute 
(about half a micron in the minute). By experimental methods he was 
actually able to check or delay the migration from the central organ of these 
cells which form the so-called Schwann’s sheaths round the peripheral nerve- 
fibres. It is these Schwann’s sheath-cells which are regarded by supporters 
of the chain-theory as the mother cells of the nerve-fibres ; but Harrison was 
able to show that nerve-fibres will grow even in cases where no sheath-cells 
exist. Oscar Schultze has tried in his last treatise to minimise the value of 
these results of Harrison’s, which we others consider almost conclusive, by 
stating that they are due to the attack of the experimental method, and do 
not therefore represent normal conditions. If that line of argument is to be 
allowed, then the results obtained by experimental interference with natural 
processes in general must be rejected, which would mean that a considerable 
part of the science of physiology would have to be rejected as unreliable, as 
being essentially based upon experimental interference of that kind. It is in 
this direction that so many excellent scientific discoveries have recently been 
made and upon which are centred the greatest hopes of progress for the future. 
To this group of phenomena and the results yielded by them we must 
assign the correct conception, arrived at by study, regarding the regeneration 
of the nerves after having been traumatically injured. It would carry me too 
far, if I were to attempt to give a detailed account of the numerous and 
extensive experimental researches upon this highly remarkable and involved 
process. After having been, with great success, made the object of research 
for a long time past by a group of distinguished physiologists, Waller, Vulpian, 
Langley, Sherrington, Vanlair, to only mention some of the more prominent 
ones, the question was also taken up by the modern histologists some years 
ago and has since been investigated by their methods; Cajal and Perroncito, 
experimenting quite independently of each other, arrived at very nearly 
coincident results. 
It has long been known that, if a nerve be severed, the central and the 
peripheral portions will reunite and the nerve be restored to use; the same 
regeneration will take place evenif a piece be cut out. It had been generally 
assumed after the date of Waller’s renowned investigations that nerve-fibres 
which are wholly or in large measure separated from the cell body with 
which they have been in direct communication, will degenerate if they do not 
speedily regain their connection with it. The German physiologist Bethe, 
however, maintained some years ago that he had succeeded in showing, by 
