164 SCIENCE PROGRESS. 



apparently disconnected provinces of physiological research 

 and speculation. It has expressed itself most clearly in 

 connection with optical phenomena, with cardiac and 

 vascular phenomena, with the pupil, with glands, and finally 

 with voluntary muscle. 



It is hardly possible within the limits of a short article 

 to do more than indicate by a few allusions and headings 

 the present drift of experiments that may fitly be grouped 

 together as illustrating inhibitory phenomena, and support- 

 ing more or less cogently the group of speculations that 

 enter into the modern doctrine of inhibition. 



With regard to the inhibitory action of the cardiac 

 vagus and the similar less clear but more general case of 

 vaso-dilatator nerves, we are still to-day, as was the case 

 thirty years ago, in presence of two theories, neither of 

 which can be admitted to have finally established itself in 

 undisputed possession. On the older theory an inhibitory 

 nerve (vagus, chorda tympani) takes effect by acting on 

 peripheral nerve-cells, organs of intermediation between 

 nerve-fibres and muscular fibres ; on the newer theory they 

 depress activity by promoting the constructive or anabolic 

 phase of nutrition. There is but little positive evidence in 

 support of this second theory ; the reversed electrical varia- 

 tion in cardiac muscle due to excitation of the vagus nerve 

 may indeed be due to a reversed trophic movement within 

 the muscle, yet can hardly be admitted as cogent evidence 

 in that respect ; we know that the nerve has an anti-tonic, 

 anti-motor effect, and that the variation with such anti-motor 

 effect should be the reverse of that witnessed with a motor 

 effect, need not excite our surprise. Nor have attempts to 

 detect a reversed thermic effect with vagus action led to 

 any more significant results. On the other hand- — and this 

 is a consideration that strangely enough seems to have 

 been wholly overlooked — the histological generalisation, 

 confirmed especially by Gaskell's labours, is precisely most 

 in harmony with the older view, and in the scale therefore 

 opposite to that of the newer view ; if the old distinction, 

 made especially with reference to vascular nerves, between 

 the cerebral or medullated nerve (vagus and chorda tympani) 



