PHYSIOLOGY, CHEMISTRY AND MORPHOLOGY. 379 



shall presently see, we must look for the definite physiological basis of 

 thought. 



Cue of the first explanations proposed for inhibition in the realm of 

 theoretical jiliysiology was, as might have been expected, purely phys- 

 ical in its character. It was thought that its phenomena might be 

 considered as analogous to those classed under interference. You 

 know that the union of two sounds may produce silence, and that from 

 two rays of light we may derive darkness. This occurs when the 

 waves that theoretically constitute their material basis meet in such a 

 way that the summit of one wave corresponds to the hollow of another 

 so that they mutually neutralize each other. The beats and the rings 

 of Newton are i^henomena of interference. Lauder lUninton,' following 

 the footsteps of Bernard- and of Eomanes,^ tried with much skill to 

 bring the phenomena of inhibition into the same category as those we 

 have just cited. It would be very interesting' to follow the learned 

 investigator in his defense of his doctrine, but I shall limit myself to 

 stating that he founded his theory upon the supposition, which appears 

 very probable in view of certain considerations, that in inhibition the 

 nervous vibrations follow two paths of unequal length, then unite in a 

 single one in which the parted waves again meet with opposite phases 

 and consequently neutralize each other. As you will observe, this 

 doctrine recalls at once the acoustic tubes invented by Herschel and 

 then successfully constructed by (^>nincke and Konig.^ 



In short, Lauder Brunton holds that movement, sensation, inhibition, 

 or stimulation are not absolute, but merely relative terms. According- 

 to him the same cell may exercise inhibitory or excito-motor functions, 

 according to the length of the waves of impulsion that pass to or from 

 it, according to the distance which these impulsions traverse and the 

 velocity with which they travel. The English exi)erimenter endeavored 

 also to find a mori:)hological basis for his doctrine in the two jn'olonga- 

 tioiis, one straight and the other spiral, with which certain nerve cells 

 are lU'ovided. This hypothesis is, as you see, inspired solely by phys- 

 ical conceptions which demand a structural form, but, however ingeni- 

 ous it may be, it does not account for the facts, and we now admit that 

 acts of inhibition are processes essentially chemical in character. 



Permit me to lay some stress upon this argument, for it will afford us 

 an opportunity of touching upon several questions of fundamental 

 importance in physiological studies. 



From a chemical point of view the functions of a living being maybe 

 included in two great categories. The first embraces the destructive, 

 analytic, catabolic, or disintegrating acts by which the individual in 



'T. Lauder Brunton. "On the nature of inhibition and the action of drugs upon 

 it," Nature, London, 1882-83, XXVII, pages 419. 436, 467, and 485. 



'■^ Bernard. La chaleur animale, Paris, 1876, page 371. 



^G. .1. Romanes. "On the locomotor system of medusse," Phil. Trans. 1877, 

 CLXVII, 730. 



<TyndalL Lectures on Sound. American edition, page 261. 



