a series of studies on absorption from the intestine by Waymouth Reid, which have just been published, in collected form, in the 'Philosophical Transactions of the Royal Society' Starting with the idea of studying the behavior of the intestinal wall when as many as possible of the physical factors which may be supposed to be concerned in absorption have been eliminated, he endeavored to realize this condition by introducing into the intestine of an animal some of its own blood-serum. When this is done the cells that line the alimentary tube are in contact on one side with blood-serum and on the other with capillary vessels containing blood, the liquid portion of which has the same composition as the serum in the intestine. Under these circumstances there could be no passage of material from the intestines to the blood by diffusion or osmosis, if the intestinal wall acted like an ordinary dead membrane. Reid found, as a matter of fact, that the serum was rapidly absorbed. That this was not due to ordinary filtration, that is, to the squeezing of the liquid through the walls of the tube, follows from the fact that in these observations the pressure in the intestines was less than in the capillaries. He comes to the conclusion that while known physical forces play a certain part in absorption, there remains an unexplained residuum. But he refuses to speculate as to the cause of the peculiar endowments of the intestinal epithelium, and is very careful to point out that what seems so inexplicable now may later on become susceptible of explanation.
Friedenthal, in a suggestive paper occupied mainly by a critique of previous work and contemporary speculation, has lately taken up his parable in favor of a complete physico-chemical explanation of absorption. According to him, what we call the selective power of the intestinal epithelium is simply the expression of the fact that there exist in those cells substances which have a greater affinity' for certain constituents of the intestinal contents than for others, just as plates of gelatine do not take up the same quantities of different salts and other compounds from solutions containing them. Such hypotheses, of course, while they have the merit of directing attention to the possibility of a complete chemical or physical solution of the problem being some day found, do not give us any information as to the peculiarities of physical structure or chemical composition which confer on the lining of the intestine, as on all living cells, powers so remarkable that when we endeavor to describe them the terms which spring spontaneously to our lips are such as we should apply to the behavior of an entire organism in relation to its environment: 'selection,' 'discrimination,' 'affinity' for substances that are useful, 'antagonism' to those which are injurious.
The study of the permeability to various substances of what we may perhaps consider as the most simply organized cells in the whole body, the colored corpuscles of the blood, promises to throw a flood of light
