Experiments in Grafting 303 
ment, was extirpated and grafted on another part of the body. 
At the time of removal he believed that the nerves had not ex- 
tended into the region of the limb. 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 limbs 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. Ithad 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 
