ADAPTATION 199 



Let us now try to take a short survey of all the regula- 

 tions discovered relating to the substitution of one kind of 

 food for another. We have said that food serves in the 

 first place as building material, in the second place as 

 fuel. It only deserves brief mention that, as all recent 

 investigations have shown, fats, carbohydrates, and albumen 

 are equally well able to serve as fuel. 1 



It is in the state of fasting, i.e. in the case of a real 

 absence of all nourishing materials, that the organism has 

 proved to be capable of regulations of the most marked 

 nature, with regard to the combustion of its own materials. 

 Respiration, we know, must go on if death is to be avoided, 

 and now indeed it has been found that this process attacks 

 the different tissues of the organism subjected to fasting in 

 such an order that, after the combustion of the reserves, 

 the most unimportant tissues with regard to life in general 



in chapter B. 5, of my Organische Regulationen. Recent discoveries of 

 Winterstein's (Zeitsclir. ctllg. Physiol. 6, 1907) have given the strongest 

 support to my hypothetic statements, and, in fact, can be said to have 

 brought the doctrine of organic oxidation to a critical point. There can be 

 no doubt that oxygen not only plays the " antipoisonous " role I had 

 assigned to it, but that it is not even of such great importance for the supply 

 of functional energy as former times had assumed. No doubt it serves to 

 drive the functional machine, but decomposition of certain chemical con- 

 stituents of the organism serves this purpose even more. The latter does so 

 in the most fundamental and original manner, so to speak, whilst oxidation 

 only burns up its products. Almost all elemental functions, in nerve-tissue 

 at least, go on very well in the absence of oxygen, provided that certain 

 "poisonous" substances, resulting from this anaerobic metabolism, are 

 constantly removed. In normal conditions that is done by oxygen, and in 

 doing so oxygen certainly assists the supply of energy, but it does not furnish 

 the whole of it. The difference between so-called " aerobic " and " anaerobic " 

 life almost completely disappears under such a view, and many so-called 

 "regulations," of course, disappear at the same time ; there is no more 

 " intramolecular respiration." 



1 But nevertheless albumen is not to be replaced altogether in vertebrates 

 by fat or carbohydrate ; it probably serves some special function besides 

 combustion, even in the adult. 



