236. NATURE AND LIFE. 
which directs itself toward and soon rejoins the opposite 
end. This bunch is made up of laminated tissue and 
nerve-tubes more slender than the original tubes; but by 
slow degrees it enlarges, grows whiter, its fibres become 
complete, and, after a lapse of from four to six months, we 
have a nerve-cord of new formation. Such a cord is repro- 
duced even when a part of the nerve six centimetres in 
length has been removed. During the time of restoration 
of the nerve-substance we remark the gradual reéstablish- 
ment of its sensor, or motor, or mixed functions. Vulpian 
and Philippeaux, who have studied this subject particu- 
larly, have ascertained that nerves absolutely severed from 
the nerve-centres can, after a period of change, thus regain 
their normal structure and properties. But the most in- 
structive experiment made by these physiologists consists 
in joining together the ends of two nerves having quite 
different functions, as for instance the motor nerve of the 
tongue and the pneumogastric nerve, and in establishing 
anatomical connection and physiological communion be- 
tween two nerve-cords which, in their usual state, have no 
mutual relation. 
In 1867, Legros discovered the reproduction of carti- 
lage, which till then had been regarded as impossible. He 
made his investigation upon dogs and rabbits, in whose 
cartilaginous tissues he had made free incisions, and at the 
end of about two months he noted a thorough renovation 
of that tissue. This is the same physiologist who first 
proved the reproduction of smooth muscular tissue, that is, 
tissue which is the organ of involuntary movement, such 
as that of the intestine. To exhaust the list of the organic 
tissues, it remained to be seen whether the muscular fibres 
in the living animal can restore, by means of like fibres, 
the losses of substance they have undergone. The following 
year Dubreuil was able to answer that question in the af- 
firmative. He cut certain muscles of Guinea-pigs through 
