870 METABOLISM. 



such cases necessary to assume a continuous process of anabolism going 

 on at the same time within the same cells. 



Upon evidence founded mainly, but not exclusively, upon the investigation 

 of certain electrical and visual phenomena, Hering has concluded that in all 

 cases where either katabolic or anabolic changes are proceeding in any portions 

 of bioplasm, they tend to render the bioplasm more and more resistant to the 

 effects of the excitation which is producing the change (reaction) ; that in any 

 given cell the longer or more strongly metabolic changes of the one character 

 have been proceeding, the greater will be the tendency towards metabolic changes 

 of the opposite character, so that even if, as may happen, in consequence of the 

 action of an external stimulus (A), anabolic changes are proceeding at first more 

 rapidly than katabolic, so that the balance is in favour of the building up 

 or assimilation processes, the reaction which is thereby provoked will, after a 

 time, by increasing the katabolism of the cell, tend again to produce a condition 

 of balance. Only in this case the balance will be struck with the general 

 bioplasm of the cell in a condition above par, as compared with that from which 

 it was assumed to start (A allonomous equilibrium). And, mutatis mutandis^ 

 increased katabolic processes due to external stimuli are (D) assumed to produce 

 by reaction an increase of anabolism in adjacent portions of bioplasm, which 

 increase becomes eventually sufficient to balance the increased katabolism 

 induced by the stimulus, so that again the metabolism of the whole cell strikes 

 a balance as it were, but now in a condition below par, as compared with the 

 normal (D allonomous equilibrium). Upon the cessation of the stimulus in 

 either case, the tendency, say, to increased anabolism being removed with the 

 stimulus, the opposite condition of increased katabolism, which was provoked 

 by the increased anabolism, will for a time prevail, and there will be a falling 

 off of the general assimilation of the cell, until what may be considered the 

 normal condition is again established, the two processes again exactly balancing 

 one another. And the same, mutatis mutandis, for the removal of a stimulus 

 which was producing a condition of increased anabolism. There is thus 

 assumed to be a sort of internal self -adjustment of metabolism in bioplasm. 



It is a part of the theory of Hering that the anabolic and katabolic changes 

 in the bioplasm are the direct or indirect cause of many, if not of all, 

 physiological phenomena exhibited by living tissue, and that the prevalence 

 of one kind of change in any portion of bioplasm will tend to start a 

 change of the opposite kind in adjacent portions. But this is a subject 

 which we need not here specially concern ourselves with, since the most 

 important application of it to the explanation of physiological phenomena 

 concerns the effects produced by the stimulation of the retina by light, and 

 will be discussed in the article dealing with this question. 



In connection with this subject, one other point must be borne in mind, 

 namely, the possibility, indeed probability, that many metabolic changes in the 

 body are not necessarily associated with the building up or breaking down of 

 bioplasm, but are effected outside the actual molecules of which the bioplasm 

 is composed, although under the influence of the activity of the bioplasm. 

 Such changes as these may be distinguished from the metabolic changes of the 

 bioplasm itself by the name of " contact changes," and they also involve both 

 the building up of complex materials and the subsequent breaking down of 

 such materials into simpler products associated frequently with oxidation. 

 Such contact changes are analogous to those which are produced by organised 

 ferments, such as yeast, outside the actual organism, although directly by its 

 activity, and they must be sharply differentiated from the changes which the 

 bioplasm itself is at the same time undergoing. This distinction will be 

 referred to again in a subsequent section. 



The understanding of the metabolic processes presupposes an acquaintance 

 with the composition of the foodstuffs and of the bodystuffs, both of which 



