fRESlDENtlAL ADbRESS. 711 



These are only a few instances of a class of mechanisms, strictly chemical in 

 character, by which the activities of remote and dissimilar organs are automatically 

 co-ordinated ; a further class of such mechanisms, although involving a chemical 

 substance convoyed by the -blood, carries out the actual regulation by means of the 

 central nervous system. An example of this class is afforded by the researches of 

 Haldane and Priestley upon the carbonic-acid gas in the pulmonary air. These 

 show that the alveolar pressure of carbonic acid in the lung spaces remains 

 constant even when the atmospheric pressure is considerately altered in 

 amount. The constancy is due to the circumstance that the respiratory nerve 

 centres are exquisitely sensitive to a rise in this carbonic-acid pressure. Any such 

 rise slightly augments the carbonic-acid tension of the pulmonary blood, which, on 

 being conveyed to the nerve centres, arouses their greater activity, and the in- 

 creased efficiency of the respiratory ventilation, thus produced, rapidly reduces the 

 amount of the very agent which is its exciting cause. ^ The researches of Hill 

 and Greenwood, with air pressures up to seven atmospheres, bear out the conclusion 

 that by this automatic mechanism the air in the lung alveoli has a practically 

 constant pressure of carbonic acid in any given individual.'- 



The introduction, in this example, of the respiratory centres and nerves raises 

 the question whether the nervous system, which is in a very special sense the 

 channel for the regulation and co-ordination of the various activities of the body, 

 may not itself be conceived to be a supreme example of an automatic physico- 

 chemical mechanism, the transference from one part to another taking place, not 

 through the flow of blood containing chemical substances, but through a more 

 subtle physico-chemical flow along the highly differentiated nervous strands of 

 which this system consists. The nervous system is not popularly regarded in 

 this light ; on the contrary it is considered to be the special seat of vital 

 directive forces, and it is held, even by some scientific men, that the nervous 

 energy which it manifests is so transcendental in its essence that it can never be 

 brought into line with those modes of energy prevailing in chemistry and physics. 

 There is, moreover, a widespread belief, founded upon conscious volitional power, 

 that nervous energy can be spontaneously created, and that even if its manifestations 

 are bound up with the integrity of certain definite nervous structures, these 

 structures only form the material residence of genii, temporarily in possession 

 endowed with the powers of hypothetical homunculi at whose bidding the 

 manifestations either take place or cease. ^ 



The complexity of nervous structure and the apparently uncertain character of 

 nervous activities furnished the older writers with plausible reasons for assuming 

 the existence of animal spirits, but the extensive researches of half a century pro- 

 gressively suggest that nervous phenomena may be regarded as the sum of par- 

 ticular physico-chemical processes localised m an intricate differentiated structure, 

 the threads of which are being unravelled by neurological technique. This chapter 

 of physiology still bristles with difficult problems and obscure points, yet the un- 

 mistakable trend of the immense advances which have been made in recent years 

 is towards the assumption that nervous processes do not in their essence diffier 

 from processes occurring elsewhere in both the living and non-living worlds. 



As regards structure it is generally assumed by neurologists that the whole 

 system is a fabric of interwoven elements termed neurons, each with a nucleated 

 nerve-cell and offshoots, one of which may be extended as a nerve fibre, whilst no 

 nerve fibre exists which is not the ofishoot of one such cell. This neuron theory 



' Haldane and Priestley, 'The Regulation of Lung Ventilation.' Journ. of 

 Physiol., xxxii. 1905. 



' Hill and Greenwood, 'The Influence of Increased Barometric Pressure on 

 Man.' Proceedings Roy. Sac, vol. Ixxvii. B, 1906, p. 442. 



* Lodge, Life and Matter (London : Williams and Norgate, 1906.) ' Matter 

 is the vehicle of mind, but it is dominated and transcended by it' (p. 123). 'Con- 

 template a brain-cell, whence originates a certain nerve-process whereby energy is 

 liberated with some resultant effect ' (p. 168). ' It is intelligence which directs ; it 

 is physical energy which is directed and controlled and produces the result in time 

 and space ' (p. 169). 



