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 reestablish- 

 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 



