Ranson, Fibers in Lesions of the Brain. 193 
ZINSKI (7) (1902) have failed to find any nerve fibers or nerve 
cells in the scars resulting from wounds in the human brain. 
IT, Experimental Observations. 
Introduction. 
We know that not all the neurones are fully developed at 
birth. The number of undeveloped neurones in the young rat 
is especially large. Dr. Axtice Hamitron has shown that 
mitotic figures are very abundant in the developing central 
nervous system of the white rat four days old(14). Harari has 
shown that the number of nerve fibers in the dorsal roots of 
the spinal nerves of the rat increases steadily long after the 
animal is mature (17). The increase in the number of fibers 
in the dorsal roots he explains as due to the development of 
the small, non-functional cells of the spinal ganglion into large 
functional cells. He has been able to show that this transfor- 
mation does occur (17). He has recently made similar obser- 
vations on the ventral roots (18), showing also in accordance 
with the observations of Harpesty (15) on the frog, that the 
number of fibers in the ventral root is greater in sections near 
the cord than in those at some distance from it. These 
observations indicate the presence in the ventral roots of nerve 
fibers that have not completed their growth. If we may infer 
the same method of growth in the central nervous system— 
and Dr. Hamitton’s (14) observations would indicate that such 
an inference is justifiable—we may assume that new nerve 
fibers are constantly being formed in the brains of young rats 
and probably in the brains of other young mammals. The 
failure to find nerve fibers in the scar when young animals have 
been operated on involves, therefore, the conclusion that nerve 
fibers which would normally have developed through this 
region have failed to penetrate the cicatricial tissue. While it 
is not inconceivable that the dense fibrous tissue filling the 
wound should act as a barrier, it seemed probable that if 
sufficiently immature animals were used nerve fibers would be 
found crossing the site of the lesion. At the suggestion of 
