ough the efforts of Eberle, Valentin,
and Claude Bernard, that this organ is all-important in the digestion
of starchy and fatty foods. It was found, too, that the liver and the
intestinal glands have each an important share in the work of preparing
foods for absorption, as also has the saliva--that, in short, a
coalition of forces is necessary for the digestion of all ordinary foods
taken into the stomach.

And the chemists soon discovered that in each one of the essential
digestive juices there is at least one substance having certain
resemblances to pepsin, though acting on different kinds of food. The
point of resemblance between all these essential digestive agents is
that each has the remarkable property of acting on relatively enormous
quantities of the substance which it can digest without itself being
destroyed or apparently even altered. In virtue of this strange
property, pepsin and the allied substances were spoken of as ferments,
but more recently it is customary to distinguish them from such
organized ferments as yeast by designating them enzymes. The isolation
of these enzymes, and an appreciation of their mode of action, mark a
long step towards the solution of the riddle of digestion, but it must
be added that we are still quite in the dark as to the real ultimate
nature of their strange activity.

In a comprehensive view, the digestive organs, taken as a whole, are
a gateway between the outside world and the more intimate cells of the
organism. Another equally important gateway is furnished by the lungs,
and here also there was much obscurity about the exact method of
functioning at the time of the revival of physiological chemistry. That
oxygen is consumed and carbonic acid given off during respiration the
chemists of the age of Priestley and Lavoisier had indeed made clear,
but the mistaken notion prevailed that it was in the lungs themselves
that the important burning of fuel occurs, of which carbonic acid is a
chief product. But now that attention had been called to the importance
of the ultimate cell, this misconception could not long hold its ground,
and as early as 1842 Liebig, in the course of his studies of animal
heat, became convinced that it is not in the lungs, but in the ultimate
tissues to which they are tributary, that the true consumption of
fuel takes place. Reviving Lavoisier's idea, with modifications and
additions, Liebig contended, and in the face of opposition finally
demonstra