Page:Popular Science Monthly Volume 74.djvu/179

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Previous to this time various theories of digestion were based upon obscure ideas of trituration, concoction, fermentation and putrefaction or whatever these words might imply. Difficult as it is for us to-day to reproduce the point of view of men who were "struggling with the spiritualistic fermentations of van Helmont, on the one hand, and with the material effervescences of Sylvius, on the other," we can nevertheless appreciate the remark of William Hunter:

Some physiologists will have it, that the stomach is a mill, others, that it is a fermenting vat, others, again, that it is a stew-pan; but, in my view of the matter, it is neither a mill, a fermenting vat, nor a stew-pan; but a stomach, gentlemen, a stomach.

The third epoch in the study of the physiology of digestion coincides with the rise of modern chemistry and may, perhaps, be said to start with the discovery of free hydrochloric acid in the gastric juice by Prout and by Tiedemann and Gmelin in 1824, soon followed by the pioneer work of Dr. William Beaumont upon Alexis St. Martin. Foster writes:

It was left for the nineteenth century to throw a new light on the nature of the gastric changes and at the same time shew that what took place in the stomach was not the whole of digestion, but only the first of a series of profound changes taking place along nearly the whole length of the alimentary canal.

Let us bear in mind, then, that although the presence of a solvent fluid in the stomach had begun to be admitted in 1803, its nature and the mode of its operation were not understood until Beaumont's classic experiments (1833) on "the man with a lid on his stomach," as St. Martin was derisively called. Réaumur (1753) experimented on a buzzard, administering to it hollow metallic capsules perforated like a sieve and containing foods within. The possibility of mechanical crushing or trituration was thereby excluded; but when the tubes were regurgitated it was found that digestion (solution) of the food materials had nevertheless taken place. Some chemical action must have been exerted; and by placing sponges in the metallic tubes, Réaumur was able to express therefrom specimens of gastric fluid. He appreciated that it possessed properties antagonistic to putrefaction; and fragmentary as his observations may appear, he introduced a-new method into physiological research. To Spallanzani was left the extension of these investigations in most fruitful fields. He well recognized the antiseptic power of the gastric secretion. With regard to the nature of digestion Spallanzani concluded (1783) in these words:

None of the three forms of fermentation distinguished by chemists under the name of spirituous (alcoholic), acid, or putrid, have any place in digestion.

His well-conceived experiments in which animals swallowed meat attached to strings by which it could be withdrawn from time to time,