_The irregular or pure thermogenic type._—And now let us conceive of the most simple _irregular or aberrant type_. Food passes from the initial to the final state without incorporation in the living cells of the organism, and without taking part in the vital functional activity. It remains confined in the blood and the circulating liquids, but it undergoes in the end, however, the same molecular disintegration as before, and sets free the same quantity of heat Its chemical energy changes at once into thermal energy. Food is a _pure thermogen_. It has fulfilled only one part of its work. It has been of slight vital utility. Does this ever occur in reality? Are there foods which would be only _pure thermogens_—that is to say, which would not in reality be incorporated with the living anatomical elements, which would form no part of them either in a state of provisory constituents of the living protoplasm, or in the state of reserve-stuff; which would remain in the internal medium, in the blood and the lymph, and would there undergo their chemical evolution? Or again, if the whole of the food does not escape assimilation, would it be possible for part to escape it? Would it be possible for one part of the same alimentary substance to be incorporated, and for the rest to be kept in the blood or the lymph, in the circulating liquids _ad limina corporis_, so to speak? In other words, can the same food be according to circumstances a _biothermogen_ or a _pure thermogen_? Some physiologists—Fick of Wurzburg, for instance—have claimed that this is really the case for most nitrogenous elements, carbohydrates, and fats; all would be capable of evolving according to the two types. On the other hand, Zuntz and von Mering have absolutely denied the existence of the aberrant or pure thermogenic type. No substances would be directly decomposed in the organic liquids apart from the functional intervention of the histological elements. Finally, other authors teach that there is a small number of alimentary substances which thus undergoes direct combustion, and among them is alcohol. _Liebig’s Superfluous Consumption._—Liebig’s _theory of superfluous consumption_ and Voit’s _theory of the circulating albumen_ assert that the proteid foods undergo partial direct combustion in the blood vessels. The organism only incorporates what is necessary for physiological requirements. As for the surplus of the food that is offered it, it accepts it, and, so to speak, squanders it; it burns it directly; and we have a “sumptuary” consumption, consumption _de luxe_.