304 Experimental Zoology 
grafted upon another individual. On the other hand, the 
limb bud of a normal individual has already received its proper 
stimulus before its removal, hence the independent development 
in it of the peripheral nerves. While the argument is far from 
convincing,’ yet the method gives promise of throwing light on a 
very difficult and obscure point. 
There is another result of interest connected with these graft- 
ing experiments of Braus. He finds when the bud of the fore leg 
is grafted in another part of the body — near the hind leg, for 
example — that in the majority of cases two legs develop, — one 
at first more advanced than the other, and the more advanced leg 
alone contains nerves. In the light of some recent experiments 
of Tornier, in which four complete hind limbs of the frog are ar- 
tificially induced by splitting the limb buds, there can be no doubt 
that the less advanced leg, in Braus’s experiment, is a regenera- 
tive product. It fails to receive nerves either from its twin leg, 
of which it is a mirror figure, or from the main body of the tad- 
pole, or at least no medullated nerves. 
Aside from the interesting questions concerned in the forma- 
tion of the nerves the experiments of Harrison and of Braus are 
important in showing that as complicated an organ as the leg 
of the frog may develop in the complete absence of peripheral 
nerves. The result shows, if true, that the self-differentiation of 
all the tissues of the leg may take place in the entire absence of 
connection by means of nerves with the central nervous system. 
' The experiments of Braus have been repeated by Harrison upon frog and 
toad embryos, the result having been briefly reported at the Toronto meeting of 
the British Medical Association, August, 1906. Contrary to Braus, Harrison 
finds that nerves are present, after a time, in limbs developed from buds which are 
transplanted from ‘‘nerveless’” embryos. These nerves have normal relation 
to the other structures in the limb, at least as far as the main features are con- 
cerned, though the finer details have not yet been studied. Furthermore, in 
cases where two limbs have developed out of a single transplanted bud, Harrison 
has found that nerves are present in both. Braus’s results are probably to be 
explained by the fact that he did not keep his specimens alive for a sufficient 
length of time after the operation. Be this as it may, Harrison’s experiments show 
beyond doubt that the nerves grow from the body of the host into the trans- 
planted appendage, and also that it is the configuration of the organs and tissues 
in the appendage that determines the course taken by the outgrowing fibers. 
