Vol.. 6, 1920 
ZOOLOGY: S. R. DETWILER 
697 
In the present experiments the grafted unit of spinal cord, carrying 
with it the neuroblastic forerunners of the seventh, eighth and ninth 
peripheral nerves, is subjected to all the factors which normally produce 
the increased proliferation of nerve cells in the limb region, and the re- 
sultant degree of development of its neurone components under these 
conditions can be compared directly with the undisturbed seventh, eighth 
and ninth segments of the host. 
The experiments were carried out on Amblystoma embryos ranging in 
age from those with completely closed medullary folds (stage 21) up to 
those with a prominent tail bud (stage 33), a stage just preceding that in 
which primary reactions first appear. Although the survival of the em- 
bryo appears to have no correlation with its age at the time of the opera- 
tion, the percentage of normal results, both structural and functional, is 
clearly a function of the age of the embryo and the most normal results 
were obtained from embryos in the stage of closed neutral folds (table 1). 
The operated animals were reared in individual aquaria and the majority 
were kept under daily observations for from 60 to 75 days. 
The effects of the transplantation upon the development of the embryo, 
the initial swimming reactions, and the functional behavior of the limbs 
are given in table 1. The bearing of these experiments upon the ques- 
tion of healing and regeneration of the spinal cord,^ and upon the develop- 
ment of the primary swimming reflexes in the light of the work of Herrick 
and Coghill,^ will be considered later. 
The observations made on the living operated animals showed that the 
limbs in fifty per cent of the cases performed normal adaptive and co- 
ordinated movements (table 1). The movements of the remainder were 
partially impaired. The defects in these consisted mainly of (1) 
imperfect flexion of both arm and forearm, and (2) extensor paralysis of 
the wrist. Only two animals of the series have been sectioned thus far 
(cases TrSc 90 and TrSc 137), in both of which the limbs functioned 
normally. A microscopic study of sections from these animals showed 
the presence of a perfectly developed brachial plexus v/ith normal in- 
trinsic nerve distribution, derived from the grafted portion of the spinal 
cord (seventh, eighth and ninth segments). Not only were the trans- 
planted segmental nerves found to be larger than the undisturbed seventh, 
eighth and ninth nerves of the host, with which they can be directly com- 
pared, but also the cord itself and the spinal ganglia showed distinct 
hyperplasia of the nerve cells (table 3, A2 and B2), thus indicating that 
the hypertropic development was due to excessive proliferation of the 
neuroblasts rather than to a compensating increase in the volume of a 
specific number of cell bodies and their axones. 
The increased development of the motor and sensory contributions to 
the fourth nerve (originally the eighth) is shown in figure 2 and also in 
table 2. In the latter are given the weights and the weight ratios of Unas- 
