THE GENERAL EFFECT OF STIMULATION 69 



rifle balls, the boundary between cell and medium would repre- 

 sent a battlefield, on which a heavy bombardment is constantly 

 taking place. The rain of shot of food and oxygen molecules 

 penetrating into the cell from the medium, would produce an 

 explosion in the existing ammunition depots, now at one point, 

 now at another, creating great breaches through which new 

 masses of shot would reach the interior. The fragments of these 

 exploding molecules would be flung out here and there into the 

 medium and would stem, now at this, now at that point the 

 besieging masses of shot. In this wild confusion on the whole 

 boundary line between cell and medium there can be no question 

 of rest or even equilibrium at any point. The human mind, 

 superior to the material world as we may deem it, is yet always 

 dependent upon the results of experience, and even in its highest 

 flights cannot become wholly emancipated from the concrete 

 objects. For this reason it is of great purport to conceive pro- 

 cesses whose dimensions cannot be observed even microscopically, 

 as enlarged and transformed to that method of expression most 

 familiar to the human mind, namely, in the field of optical pre- 

 sentation. This method is of great help in aiding our under- 

 standing, and likewise here, even in the resting state, the cell is 

 constantly exposed to local effects of stimulation, now at one 

 point, now at the other. The conception of the metabolism of 

 rest is, therefore, in a strict sense fiction. 



Nevertheless, the conception of the metabolism of rest as an 

 abstraction can be of value provided always that it is strictly 

 and definitely limited. It must, for instance, not be applied to 

 short periods of time. The continued local and temporary re- 

 sponses to stimulation constitute a mean value which, although 

 composed of numberless small sub-threshold responses, we can 

 still call a metabolism of rest. Weak stimuli have, however, as 

 already seen, the property, provided their influence is constant, 

 of eifecting an adaptation to the stimulus on the part of the living 

 organism, so that the stimulus becomes a vital condition for this 

 state of the organism. Hence the continued existence of a vital 

 process resulting from the constant action of stimulation is made 

 possible. That which we are in the habit of calling metabolism 



