446 ELECTRICITY IN THE PHENOMENA OF ANIMAL LIFE. 



It presents itself to us, therefore, not only in tlie complex organism, 

 but even in the last result of its structural subdivision in the single 

 cell, in which it still exhibits the same essential character by which it is 

 sufiicieutly defined. 



It is not limited by particular morphological conditions. Organic; 

 form and structure may vary almost endlessly with a condition of the 

 medium without the essential character of vitality thereby disappearing. 



In order that this vital reaction may take place three general condi- 

 tions are necessary: First, the simultaneous presence together of the 

 prime materials essential to the reaction; secondly, a particular state 

 of distribution of these prime materials, from which may result the 

 heterogeneity indispensable to the progress of the reaction, and, finally, 

 such arrangements as shall permit the energy liberated by the reaction 

 to be consumed, utilized, or transformed, either on the spot or outside 

 the field of the reaction. 



II. — <^)F OXIDATION IN THE ORGANISM. 



Among the chemical phenomena, varied as they are, which the living 

 organism presents to ns there is one, that of oxidation, which is dis- 

 tinguished from all the rest by its generality of extent and its prepon- 

 derant importance; we may even say that, so far as the higher animals 

 are concerned, oxidation is the essential chemical phenomenou of life 

 and the others are but of secondary character. - - - The princi])al 

 seat of vital activity is to be found in protoplasm submitted to the 

 action of oxygen. It is protoplasm which forms cells; it is by it that 

 they live and are nourished. As for the protoplasm itself, it derives 

 its material from the various forms of food, solid, liquid, and gaseous, 

 which are thus the prime source of the energy develoi)ed in the organ- 

 ism. - - - But before broaching the subject of chemical change as 

 it occurs in the organism let ns first consider a simjile phenomenon, and 

 one with which we are familiar; we shall thus make clearer the state- 

 ment which is to follow. 



When we plunge a piece of perfectly pure and homogeneous zinc into 

 acidulated water, as long as the metal remains isolated in the liquid we 

 observe no reaction, save that at the first moment of introduction a 

 difterence of electric potential is immediately established, but all is 

 limited to this. 



If, on the other hand, we connect the zinc with the acid by a sub- 

 stance less oxidizable than this metal, immediately an electric current 

 is set up and reaction between zinc and acid takes place. 



Simi^le contact then does not suflice to bring about reaction; it can 

 but produce a sort of orientation of tension, or, if one please so to i)ut 

 it, a new state of equilibrium of the particles, in which there come in 

 an electro-motive ibrce and a counter electro-motive force equal and 

 op])osed thereto. 



