86 POPULAR SCIENCE MONTHLY. 



a series of studies on absorption from the intestine by Waymouth Reid, 

 which have just been published, in collected form, in the Thilosophical 

 Transactions of the Eoyal 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 intro- 

 ducing 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 Avith 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 suscep- 

 tible 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 



