6 THE CARBOHYDRATE ECONOMY OF CACTI. 



It seems highly improbable that the life processes consist of any one 

 series of chemical changes or are dependent upon any particular molecule 

 or chemical group. But rather the simpler life processes entailing energy 

 changes may perhaps be regarded as a complex of interrelated chemical 

 changes taking place in a certain medium or substratum. This medium, 

 colloidal dispersion, mixture, or aggregate of various substances is the seat 

 or substratum in which the various chemical reactions take place, the nature 

 and course of which are determined by the complex of properties associated 

 with water control, surface phenomena, and of course catalysts (such as 

 inorganic salts and enzymes). These colloids do not enter into or support 

 the chemical reactions or do so probably only in a rather indirect manner, 

 serving primarily as a physical medium. Such a system would be of a 

 heterogeneous nature and, of course, of the most complex type, and capable 

 of various adsorption phenomena productive of localized action which would 

 influence the function as well as the structure of the system. In fact, such 

 a hypothesis would demand that the substratum be relatively stable, that the 

 colloidal material once formed does not break down as readily as the other 

 substances, or only after the supply of these has been exhausted. This does 

 not mean actual or chemical stability, but rather relative to the other sub- 

 stances under the existing physiological conditions, as, for instance, rela- 

 tively slightly dissociated by salts or other catalysts and resistant to the 

 action of enzymes. 



This colloidal material may also in part be composed of substances which 

 do not undergo complete disintegration and thus are not excreted from the 

 cell. The proteins in most plants, due to the high synthetic power charac- 

 teristic of plants, are rarely so drastically affected that they are not again 

 reconstituted; these substances are thus relatively stable in the sense that 

 under normal conditions they do not disappear in the course of metabolism. 

 The cell substratum or protoplasm should then be regarded as a complex of 

 substances of relative stability in which the more sensitive substances break 

 down with the liberation of energy, the formation of products of catabolism, 

 and the synthesis of other more complex substances in varying amounts. 

 It is, then, the combination of the intricate chemical reactions taking place 

 in this heterogeneous colloidal system that constitutes the principle of 

 energy change of living processes. While the chemical reactions are influ- 

 enced by the nature of the medium, the latter is also a product of the 

 chemical processes. 



The conception of protoplasm as a tremendously complex " living " pro- 

 tein molecule arose before any considerable chemical knowledge of this 

 group of substances had been gained. Through the extensive researches of 

 Fischer, Kossel, Abderhalden, and many others it has become apparent 

 that the conception of such an enormous complexity and sensitiveness of the 

 proteins was rather unwarranted. Furthermore, the theory that proteins, 

 carbohydrates, and fats are synthesized into elaborate complex substances 

 before they break down and yield energy was necessitated by the prevalent 



