Experiments in Grafting 303 



ment, was extirpated and grafted on another part of the body. 

 At the time of removal he beUeved that the nerves had not ex- 

 tended into the region of the hmb. The bud developed in its 

 new location into a complete structure possessing the normal 

 nerves, which were larger than the body nerves with which 

 they were found to be connected. Braus concluded that the 

 nerves of the hmbs do not grow out from the spinal cord, as His 

 and his followers claim, but differentiate in the limb itself. 

 In another experiment the problem has been examined in a 

 different way. It had been shown by Harrison that if the dorsal 

 part of the young embryo of the frog, including the nerve cord, 

 be removed, the embryo may continue for a time to develop. 

 Braus carried out this operation, and after the bud of the hind 

 limb had appeared he removed it, and transplanted it upon an- 

 other normal embryo. The bud developed into a normal limb, 

 except that it entirely lacked nerves. In this respect it differed 

 from the preceding case. It might appear that in the first case 

 the nerves had already grown into the limb, hence their develop- 

 ment when the limb was transplanted. This interpretation, 

 Braus states, is negatived by two considerations : first, he could 

 not find that the nerves had grown into the limb at the time of its 

 removal ; second, even if they had we should expect them to de- 

 generate when removed from their central connections. More- 

 over, if nerves grew out from the central nervous system into the 

 grafted limb, it is not evident why they should grow out in the 

 first case given above and not in the present case. Braus inter- 

 prets his results as follows : The peripheral nerves are formed out 

 of the intercellular protoplasmic connections between the cells of 

 the embryo. The stimulus that leads to their development into 

 nerve bundles originates from the nerves that start from the 

 central nervous system ; hence the nerves themselves appear as 

 though extensions of the nerve processes of the cells coming 

 from the nerve cord. If the central nervous system is destroyed 

 at an early stage, the time may pass by when the intercellular con- 

 nections in the limb bud can respond to the central influence, 

 hence the failure of such a limb bud to develop its nerves when 



