304 MESSRS. F. GOTCH AND V. HORSLEY 



nerves were examined and the average difference amounted to only 005 Dauiell, 

 whilst the highest difference observed was 007, and the lowest 003. This diminu 

 tion in the case of the Monkey cannot be attributed to the smaller size of the sciatic 

 nerve in the common Macaque Monkey, which is generally experimented upon, since in 

 two cases large Rhcesus Monkeys with big nerves were used, and in these (333), (368) 

 the highest difference is 007, and the average 0055. (Compare the proportions of the 

 nerves as shown in Plates 30-35.) 



Moreover, as the previous results obtained by FREDERICQ show, the amount of the 

 difference does not vary directly with the size of the nerve when different classes of 

 animals are used, of which the high difference in the Rabbit and the low difference in 

 the Horse is a notable illustration. 



It will be seen that the spinal cord resting difference in the Cat and Monkey 

 exhibits the same contrast as that of the sciatic nerves. 



It has been stated that the resting difference in the nerve is not perceptibly affected 

 by division of the spinal cord, when the division is carried out at the time of the 

 observation. It appears, however, that section of the cord one to two months prior to 

 the experiment does affect the amount of the difference. This influence, though small, 

 seems to be sufficient to enable the observer to judge, when the cord lesion has been 

 unilateral, upon which side it is situated. 



Thus in an animal, Cat (227), in which the left lumbar posterior roots had been 

 divided, the left nerve difference was 007, that of the right 009. In another animal, 

 Cat (223), in which the right posterior column had been divided, the right nerve 

 difference amounted to 005, the left 008, and in an animal (259) upon which a 

 hemisection on the left side had been effected, the left nerve difference was 007, the 

 right &quot;008. 



In one case after section of both posterior columns (Cat) the difference in each nerve 

 was 012, an amount which is somewhat in excess of the average. 



2. Alterations in the Resting Difference, 



The alterations in the difference occurring whilst the nerve was under observation 

 may be divided into : 



(a.) Those due to physical changes, affecting the contacts and derivation currents, 

 and due to loss of moisture from evaporation, change of temperature, &c. 



(6.) Those only to be accounted for as connected with slow physiological changes in 

 the tissue, the chief agent in such alteration being loss of vitality, due to arrest of 

 the circulation, and to other causes. 



(c.) Those directly connected with the production in the tissue of excitatory 

 physiological processes. 



We will now examine these separately in detail. 



(a.) Physical Changes. With regard to the effect of physical changes, such as 



