426 ELEMENTARY PROJiLEM.S IN PH VSK )L(>GY. 



the world of lite preseuts itself to the iaqiiiring mind of man. Seen 

 from the morphological side, the whole plant and animal kingdom con- 

 stitutes the unfolding of a structural plan which was once latent in a 

 form of living material of great apparent simplicity. From the phys- 

 iological side this apparently simple material is seen to be capable of 

 the discharge of functions of great complexity, and therefore must 

 possess corresponding 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 endeavor to show you, the exist- 

 iug 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 absorp- 

 tion of oxygen, the discharge of carbon dioxide and water and am- 

 monia, 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 i^roperties of plants 

 and animals on chemical action. But all the othe^ activities which 

 have been mentioned are fundamentally chemical. 



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

 process. For three quarters of a century after the fundamental discov- 

 eries of Lavoisier and Priestley (1772-'76) the accepted doctrine was 

 that the effete matter of the body was brought to the lungs by the cir- 

 culation 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 oxy- 

 gen must be conveyed as such, by the blood stream to do its purifying 

 work in all parts of the body. 



Between 1872 and 1876, as the result of an elaborate series of investi- 

 gations of the respiratory process, the proof was given by Pfliiger* 

 that the function of oxygen in the living organism is not to destroy 

 effete matter either here or there, but rather to serve as a food for pro- 

 toplasm, which so long as it lives is capable of chargiug itself with this 

 gas, absorbing it with such avidity, that although its own substance 

 retains its integrit^^, no free oxygen can exist in its neighborhood. The 

 generally accepted notion of effete matter waiting to be oxidized, was 

 associated with a more general one, viz, that the elaborate structure of 

 the body was not permanent, but constantly undergoing decay and re- 

 newal. What we have now learnt is that the material to be oxidized 

 comes as much from the outside, as the oxygen which burns it, though 

 the re-action between them, i. e., the oxidation, is intrinsic, i. e., takes 

 place within the living molecular frame- work. 



*Pfluger's Archiv, 1872, vol. vi, p. 43; and 1875, vol. x, p. '251. "Ueber die pliysi- 

 ologische Verbrennuug in den lebendigen Orgauismen." 



