716 TRANSACTIONS OF SECTION I. 



restraint — the vvbip and the reins. The possession by the central nervous 

 mechanism of inhibitory powers is remarkable both for its extent and its deli- 

 cacy. It appears more and more probable that this is achieved by the propa- 

 gation of nervous impulses of the ordinary type. Thus, recent researches by 

 Sherrington show that the propagated impulses from a given central mass may, 

 although normally inhibitory to the centrifugal discharge of another mass, become 

 directly incentive if the second controlling centre has its excitability abnormally 

 augmented by strychnine, tetanus toxin, &c.' As regards their fundamental charac- 

 ters it thus appears that both augmenting and inhibiting impulses belong to the 

 same category. Moreover, such theories of central inhibition as embrace all the 

 phenomena involve as their essential basis the cutting-oif of the potent centripetal 

 supply to the inhibited centre. In the interference theory this cutting-off is 

 assumed to be caused by the arrival of other nerve impulses which, breaking into 

 the path of normal centripetal flow, obstruct and run counter to this potent stream. 

 In the ingenious drainage theory, propounded by McDougall, the cutting-oft" is an 

 indirect one, it being assumed that the new stream enters other side-channels, and 

 thereby opens up a short circuit through which the potent ones drain away without 

 I'eaching the centrifugal centre. Even Langley's conception of receptive substances 

 played upon by impulses must be associated with a check in the efficiency of the 

 continuous centripetal supply. 



From the foregoing it appears that the physiologist has definite grounds for 

 believing that, as far as present knowledge goes, both the production and cessation 

 of central nervous discharges are the expression of propagated changes, and that 

 these changes reveal themselves as physico-chemical alterations of an electrolytic 

 character. The nervous process, wliich rightly seems to us so recondite, does not, 

 in the light of this conception, owe its physiological mystery to a new form of 

 energy, but to the circumstance that a mode of energy displayed in the non-living 

 world occurs in colloidal electrolytic structures of great chemical complexity. 

 There is a natural prejudice against the adoption of this view, but such prejudice 

 should surely be mitigated by the consideration that this full admission of 

 physiology into the realm of natural science, by forcing a more comprehensive 

 recognition of the harmony of Nature, is invested with intellectual grandeur. 



With such questions as the essential meaning of consciousness and the inter- 

 pretation of the various aspects of mind revealed by introspective methods, the 

 physiologist, as such, has no direct concern. For his purpose states of conscious- 

 ness are regarded merely as signs that certain nervous structures are in a state of 

 physiological activity ; and he thus limits the scope of physiology to the objective 

 world. This limitation of physiology does not prohibit a treatment of the sub- 

 jective world along lines calculated to display that intellectual causative array 

 which characterises science; it merely indicates that this particular application of 

 scientific method is not physiology, but that something else, still more profound, 

 which is now termed psycho-physics. 



But if objective phenomena form the subject-matter of the physiologist, then 

 'the legitimate materialism of science ' must constitute his working hypothesis ; 

 and his ' well-defined purpose ' must be to adapt and apply the methods of physics 

 and chemistry for the analysis of such phenomena as he can detect in all physio- 

 logical tissues, including the nervous system. The trend of such a strictly physio- 

 logical analysis is towards a conception in which the highest animal appears as an 

 automaton composed of differentiated structures exquisitely sensitive to the play 

 of physical and chemical surroundings." The various parts of the animal body are 

 linked by circulating fluids and by one special structure, the nervous system ; in 

 this linking of parts the physiologist detects the working of automatic chemical 

 mechanisms of great delicacy which, once developed, are retained and perfected in 

 proportion as they efficiently regulate the various bodily activities and co-ordinate 



' Sherrington, Proc. Roy. Soc, vol. Isxvi. B, pp. 269-297. (London, 1905.) 



2 See Huxley ' On the Hypothesis that Animals are Automata,' Evening Address ; 



Brit. Assoc, Belfast, 1874. Republished in Collected Essays, vol. i. (Macmillan, 



1904.) 



