TRANSACTIONS OF SECTION D. 609 



of the discharge of functions of preat complexity, and therefore must possess 

 correspomiincr complexity of mechanism. It is the nature of this invisible 

 mechanism that physiology thirsts to know. Although little progress has as yet 

 been made, and little may as yet be possible, in satisfying this desire, yet, as I 

 shall endeavour to show you, the existing knowledge of the subject has so far 

 taken consistent form in the minds of the leaders of physiological thought, that 

 it is now possible to distinguish the direction in which the soberest speculation is 

 tending. 



The non-developmental vital functions of protoplasm are the absorption of 

 oxygen, the discharge of carbon dioxide and water and ammonia, the doing of 

 mechanical work, the production of heat, light, and electricity. All these, excepting 

 the last, are known to have chemical actions as their inseparable concomitants. 

 As regards electricity we have no proof of the dependence of the electrical 

 properties of ]ilants and animals on chemical action. But all the other actinties 

 which have been mentioned are fundamentally chemical. 



The Ultra-Microscopical SU'uciure of Living Material. 



Let us first consider the relation of oxygen to living matter and vital process. 

 For three quarters of a century after the fundamental discoveries of Lavoisier 

 and Priestley (1772-76), the accepted doctrine was that the eflijte matter of 

 the body was brought to the lungs by the circulation and burnt there, of which 

 fact the carbon dioxide expired seemed an obvious proof. Then came the discovery 

 that arterial blood contained more oxygen than venous blood, and consequently 

 that oxygen must be conveyed as such by the blood stream to do its purifying work 

 in all parts of the body, this advance in the understanding of the process being 

 crowned a few years later by the discovery of the oxj-gen-carrying properties of the 

 colouring matter of the blood, in which the present President of the Royal Society 

 took so prominent a part. Finally, between 1872 and 1876, as the result of an 

 elaborate series of investigations of the respiratory process, the proof was given by 

 Piliiger •_ that the function of oxygen in the living organism is not to destroy efleto 

 matter either here or there, but rather to serve as a food for protoplasm, which so 

 long as it lives is capable of charging itself with this gas, absorbing it with such 

 nvidity, that although its own substance retains its integrity, no free oxygen can 

 exist in its neighbourhood. This discovery, of which the importance is coimparable 

 with that of Lavoisier, can best be judged of by considering its influence on other 

 fundamental conceptions of the vital process. The generally accepted notion of 

 effete matter waiting to be oxidised was associated with a more general one, viz. 

 that the elaborate structure of the body was not permanent, but constantly under- 

 going decay and renewal. What we "have now learnt is, that the material to be 

 oxidised comes as much from the outside as the oxj-gen which burns it, though the 

 reaction between them, i.e., the oxidation, is intrinsic, i.e., takes place within the 

 livinu molecular framework. 



Protoplasm, therefore, understanding by the term the visible and tangible 

 presentation to our senses of living material, comes to consist of two things — 

 namely, of framework and of content — of channel and of stream— of acting part 

 which lives and is stable — of acted-on part which has never lived and is labile, 

 that is, in a state of metabolism, or chemical transformation. 



If such be the relation between the living framework and the stream which 

 bathes it, we must attribute to this living, stable, acting part a property which is 

 characteristic of the bodies called in physiological language ferments, or enzymes, 

 the property which, following Berzelius, we have for the last half century expressed 

 by the word cataliftic ; and use, without thereby claiming to understand it, to 

 indicate a mode of action in which the agent which produces the change does 

 not itself take part in the decompositions which it produces, 



• Pfliigcr's Archil', vol. vi., 1872, p. 43, and vol. x.. 1875, p. 251. ' Ueber die 

 physiolonrische Verbrennung in den lebendi^reu Orjrauismen.' 

 1889. 



