LEWES ON THE SKN'SOliY ANJ> MOTOE FUNCTIONS OF NERVES. 179 



brain ;" and of " motor-impulses" being " conveyed to the muscles ;" it 

 is the stimulated nerves which excite the activity of brain and muscles, 

 as the spark excites the explosive activity of gunpowder. We do not 

 need three kinds of Contractility for flexors, extensors, and sphincters ; 

 nor do we need three kinds of Neurility for muscles, centres, and glands. 

 One property serves for the three functions. The differences in the 

 functions do not depend on the organs themselves, but on the connexion 

 of these organs with others ; the same organ (nerve) which, in con- 

 nexion with a muscle, produces motion, in connexion with a gland 

 would produce secretion. 



The idea of different Neurilities must, therefore, be rejected. The 

 two nerves having similar structure must have similar properties ; but 

 these properties may be put to different uses. My critic in the British 

 and Foreign Medical Review seems to have wholly misunderstood me ; 

 and thinks that had I been "longer engaged in the study of physiology," 

 I should be " less inclined to rest upon an apparent similarity of struc- 

 ture as justifying an inference of identity of property." Perhaps his 

 longer study will enable him to enlighten me on this point ; at present 

 my conviction is, that if the similarity were only apparent, it would amply 

 justify the inference ; whereas, if the similarity were real, and not appa- 

 rent only, it would carry a demonstration. My critic seems to think other- 

 wise ; and he is kind enough to say that my " dogmatism on this point, 

 indeed, is absolutely confounding to those who have been accustomed to 

 look with marvel at the diversity of operations performed by elementary 

 parts which present no appreciable structural differences." One natu 

 rally feels a little perplexed at having confounded others by one's dog- 

 matism, when the point in question is so excessively simple as the dis- 

 crimination between properties and uses. I would, therefore, submit 

 that the operations performed by means of chain cables, tenpenny nails, 

 marling spikes, and grappling irons, though various enough, are not 

 generally held as evidence that the iron of which they are all composed 

 has different properties in each. I never denied that different nerves 

 had different functions, but only that they had different properties. If 

 any one conceives that the anterior roots send forth nerves having a 

 Neurility as widely opposed to that of the nerves issuing from the pos- 

 terior roots as Motion is to Sensation, let his evidence be produced. If 

 he conceives that the anterior nerves will only act in one direction, and 

 the posterior in another and contrary direction, so that the motor nerve 

 cannot excite a centre, and the sensory cannot excite a muscle or a gland, 

 let him produce his evidence. Meanwhile, I will suggest the evidence 

 against such a notion. 



It has been proved by Schiff, and others, that the nerve loiU conduct 

 both ways ; not only will it conduct electricity, it will conduct its own 

 proper stimulus. In other words, it has been shown experimentally 

 that Neurility will act both in the centripetal and centrifugal directions. 

 I will now call attention to a still more striking fact, one which has 

 strangely enough been overlooked, probably because investigators were 

 seeking only the phenomena of sensation and motion ; a fact which dis- 



