ON THE MAMMALIAN NERVOUS SYSTEM. 313 



The examination was made as rapidly as possible in the order given below, and at 

 the various regions indicated. 



Lumbar segment 



From 4th lumbar -035 to about llth dorsal '04. 



Dorsal segment 



From about llth dorsal '043 to about 3rd dorsal '037. 



Cervical segment 



From about 3rd dorsal '035 to about 3rd cervical '037. 



After a quarter of an hour's interval, the experiment was repeated in the reverse 

 order, commencing with the cervical and ending with the lumbar segment. The 

 results were as follows : 



Lumbar segment -035 '036, 



Dorsal segment -030 '021, 



Cervical segment -031 -029. 



In this experiment, the dorsal cord resting difference is greater than that obtained 

 from either enlargement, but it is more affected by the injurious influences of 

 severance and loss of circulation. It must be remembered, that there are three 

 possible factors in the severed cord which determine the amount of the resting 

 difference in any given region ; the number of fibres, the amount of grey matter, and 

 the maintenance of vitality through circulation, &c., this last being influenced by size 

 of vessels, &c. All these vary in different regions, but the first is preponderant in the 

 dorsal region, the others in the enlargements. 



(b.) Cord Divided Longitudinally. In the course of experiments to be detailed 

 hereafter, we had occasion several times to divide the cord longitudinally into two 

 halves. This division was carried out under all the precautions indicated in the section 

 dealing with operative procedure, and was always in the form of a longitudinal cut 

 connecting the anterior and posterior fissures, and extended from the cross section of 

 the divided cord for three centimetres. Since it was our main object to establish a 

 quantitative comparison between the crossed and the direct excitatory cord effect 

 evoked by cortical stimulation, the cord was generally divided in the lower dorsal 

 region, and the lower end of the fragment on the central side of the division was split 

 in the fashion just described. (See Plates 31, 33.) The results in seven Cats and five 

 Monkeys are given in Appendix B, III. 



Each half of the split cord was connected with a pair of non-polarisable electrodes 

 by the cable arrangement already indicated, and the amount of the difference between 

 the cross section and the surface in each then determined. It will be seen that the 

 average amount for each side in the Cat is '02 Daniell, the highest and lowest readings 



MDCCCXCI. B. 2 s 



