324 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



The only assumption involved in this hypothesis of the 

 orifrin of the nerve force is that a thermo-electric current 

 can be generated between soft tissues of different composi- 

 tion or structure. Mr. Garrod calls upon physicists to decide 

 this question experimentally, and thus prove, or dispi'ove, his 

 hypothesis. He considers the nervous system perfectly suit- 

 ed to the distribution of a current so generated, there being- 

 two sets of conductors : the one to carry the currents from 

 the skin to the central organ, which arranges the direction 

 they must take ; and the other to send them on to their des- 

 tination. These are found in the afferent and efferent nerves. 

 No return current or conductor is necessary, since the termi- 

 nation of the nerves in the skin, where they lose their insu- 

 lated coverings, places the extremities of the afferent and ef- 

 ferent nerves in communication throuoh the intervention of 

 the mass of the body tissues. 



This hypothesis, in Mr. Garrod's opinion, explains some of 

 the special phenomena of the nervous system. Thus it is 

 well known that the impulse to action is much more power- 

 fully felt in cold weather than in summer, when the air is 

 hot and the temperature of the surface is higher. Again, in 

 a hot-water bath, where the temperature is nearly that of 

 the body, great lassitude is experienced, in consequence, as is 

 suggested, of the cessation of the nerve current, consequent 

 on the approximation of the temperature of the surface of the 

 body to that of the interior. This faintness is immediately 

 removed by the application of a cold douche. 



When great muscular exertion is to be sustained, as in 

 running or rowing, the clothes must be very thin, as instinct 

 teaches us that the surface of the body should be kept cool. 

 As the termination of the nerves in the skin must correspond, 

 on this hypothesis, with the cooled end of the thermo-electric 

 battery, the brain, which is well supplied with blood, and is 

 the part of the body to which most of the nerves are direct- 

 ed, must be compared w^itli the heated end ; and as, by the 

 conversion of heat into electric current, the nerve force is 

 developed, it is evident that heat, to a certain extent, must 

 disappear, as such, in the brain, and that that organ must be 

 colder than the blood which enters it. This is precisely in 

 accordance with the observations of Dr. John Davy in the 

 case of the rabbits he experimented upon, the results of 



