The Major Metabolic Fuels

organized work. It is not surprising, therefore, that the active groups of the enzymes should only be capable of acting in association with a carrier of a given structure. For, orderly biological processes are unthinkable without presupposing structure, and it is therefore out of the question that any living constituent of protoplasm could consist of structureless, fluid, independently displaceable particles. It is for this reason that colloid chemistry, based, as it is, upon the disperse principle, has thrown so little light upon the submicroscopic structure of protoplasm. For the cell certainly is not a pouch filled with ultramicrons suspended in a fluid, whirling about haphazardly and in confusion; it is, on the contrary, a wonderful system, the intrinsic structure of which, could it but be seen, would assuredly fill every observer with an enthusiasm equal to that which microscopic cytomorphology inspires."