306 



THE CAT. 



[CHAP. ix. 



of which it has heen deemed a special form. II. It has been, and 

 is by many, supposed to be merely one form of physical force a 

 mode of motion specially transformed by the molecular structure of 

 the matter through which it passes. III. It has been, and is by 

 many, deemed to be a special kind of vital force peculiar to nerve 

 substance. 



As to the first hypothesis, the slow rate at which the nerve 

 impulse travels is alone sufficient to refute it. Whereas light 

 travels at the rate of 40,000 miles in a second, and electricity, along 

 a wire, at the rate of 462,000,000 feet per second nervous influence 

 appears to pass but at a rate varying from 80 to a little above 

 200 feet in a second. Again, the interposition of a piece of wire 

 between the cut ends of a bisected nerve does not serve to conye) 7 " 

 the nervous influences, and cold diminishes, instead of increasing, 

 nervous activity. Moreover, bruising a nerve impedes its action ; 

 but no similar effect could be produced on a wire serving for the 

 conveyance of electricity. Moreover, the intensity of nervous action 

 increases according to the length of the nerve it traverses, which is 

 no property of electrical conduction. 



As to the second supposition that nervous activity is merely one 

 condition of physical force it is but one form of the error which 

 would explain all vital action as physical, in spite of the manifest 

 impossibility of explaining generation, to say nothing of sensation in 

 any such way. But one special hypothesis of the kind is that 

 which views nervous conduction as the serial change of hypothetical 

 nervous molecules from one physical condition to another, nerves 

 being supposed to be made up of parts capable of being easily made 

 to pass to and fro from one physical state to another as a series of 

 bricks set on end, may be alternately erected and thrown down, the 

 falling of one inducing the fall of its neighbour, and thus carrying 

 on serially an impulse initiated at one end of the series. If such a 

 conception is of any utility, as a working hypothesis to elucidate 

 nervous physiology, there can be no objection to its use, but it must 

 not be supposed to afford any real explanation. 



As to the third supposition that nervous activity is a peculiar 

 vital force it is again no real explanation, though it is perhaps the 

 most appropriate expression of the facts. It is manifest that the 

 living body is capable of varied activities, and that its several parts 

 exercise functions of different kinds. It is then little more than a 

 truism to say that nervous tissue is the seat of nervous force. It is 

 unquestionable that its integrity and stimulation are the conditions 

 sine qua non for the manifestation of all the highest animal activities, 

 while different degrees and kinds of injury inflicted on it result in 

 different degrees and kinds of impairment of such activities, and, 

 when carried beyond a certain point, end in the destruction of all 

 vital activities whatever even of the merely vegetative or organic 

 activities. Nervous activity then is the vital activity of a living 

 organism as it energizes in its nervous system. But the conception 

 of a particular kind of vital force must stand or fall with the con- 



