ON THE MEDULLATED NERVE FIBERS CROSSING 
tobe star Or, LESIONS, IN, THE) BRAIN) OF 
THe WHITE RAT. 
By S. WALTER Ranson. 
Instructor in Anatomy, Marion—Sims— Beaumont Medical School St. Louis University 
(From the Neurological Laboratory of the University of Chicago.) 
With Plate VII. 
I. Htstorical Review. 
The results of research on the regeneration of the neu- 
rones in the central nervous system of vertebrates have varied 
greatly according to the age and zoological position of the 
animals used for experiment. For this reason the observations 
found in the literature have been grouped for review according 
as they were made on amphibians, reptiles, birds, or mammals. 
It should be born in mind in considering this question, that 
regeneration in the central nervous system may involve either a 
proliferation of neurones as a whole, 1. e., the growth of new 
elements resulting from cell division, ora restitution of parts of 
mature neurones which have been mutilated. 
Spinal Cord of Amphibia. 
In the spinal cord of amphibia the process has been de- 
scribed quite fully by BarrurtH (2) (1891), who amputated 
the tails of frog larvae and was able to show that the cells 
lining the central canal became amoeboid and arranged them- 
selves so as to close the canal. These cells then proliferated 
by indirect division, forming a tube which extended backward 
into the new tail. From this tube the new spinal cord with its 
ganglia and nerves developed. FRralissE (12) (1885) found a 
normally functioning cord in the regenerated tail of an amphib- 
ian larva. Harrison (16) (1898) secured results agreeing with 
