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 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, carbo-*hydrates, 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.

In this connection arose a celebrated discussion which still divides physiologists. If we disengage the essential body of the discussion from all that envelops it, we see that it is fundamentally a question of deciding whether a food always follows the same evolution whatever the circumstances may be, and particularly when it is introduced in great excess.