STUDIES ON REGENERATION IN THE SPINAL CORD! 
Il. THE EFFECT OF REVERSAL OF A PORTION OF THE SPINAL CORD 
AT THE STAGE OF THE CLOSED NEURAL FOLDS ON THE 
HEALING OF THE CORD WOUNDS, ON THE POLARITY 
OF THE ELEMENTS OF THE CORD AND ON 
THE BEHAVIOR OF FROG EMBRYOS 
DAVENPORT HOOKER 
Anatomical Laboratory of the School of Medicine, Yale University, New Haven, 
Connecticut 
NINE FIGURES 
In the first paper of this series, the attempt was made to ana- 
lyse the processes leading to the reunion of the spinal cord in 
frog embryos, following its simple but complete severing just 
after the closure of the neural folds. The primary purpose of 
the experiments upon which this paper is based was to test the 
effect. of reversal of a piece of the spinal cord on the healing of 
such wounds in embryos of the same age. It soon became ap- 
parent that this purpose would be overshadowed in importance 
by the evidence which such experiments would give upon, (1) 
the nature of the primary responses of the embryos used, (2) 
the nature of the early nerve development, both within and with- 
out the spinal cord, and (3) the effect of the reversal on the 
polarity of the cord and the neurones. The results detailed 
below throw light upon some of these points. 
Reversal end-for-end of portions of the central nervous sys- 
tem has been carried out by several investigators, notably by 
Harrison (’98, ’03), and by Spemann (712). As described in his 
earlier paper, Harrison grafted young frog embryos together by 
1T am indebted to the Loomis Research Fund of the Yale University School 
of Medicine for much of the apparatus used in these experiments. This work was 
reported in brief before the American Association of Anatomists, 1915 (’16). 
421 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 27, NO. 4 
JUNE, 1917 
