BE CENT PHYSIOLOGY. 85 



The fact that the cell suffers also is a striking illustration of the essen- 

 tial unity of the nerve-cell and all its branches, whether they are long 

 or short — three feet in length, as the axones that run from the lower 

 part of the spinal cord to the foot may be, or a thousandth of an inch, 

 like some which arise and terminate within the gray matter of the 

 cord and brain. 



Simpler, at first sight, in their action and organization than nerve- 

 cells or muscular fibers are the gland-cells which secrete the digestive 

 juices. The cells of the kidney which separate from the blood the con- 

 stituents of the urine, and the cells wliich line the intestine and are 

 engaged in the absorption of the food appear to be simpler still. And 

 simplest of all are the flat, scale-like cells that line the lungs and have 

 to do with the taking in of oxygen and the elimination of carbonic acid 

 and the similar cells which form the walls of the capillasies and are 

 concerned in the production of lymph. Accordingly we have seen of 

 late years, in connection with researches on the functions of such cells, 

 a revival of formal discussion of the general problem of physiology: 

 whether the vital processes can be completely explained in terms of the 

 laws of unorganized matter. This is a question which has had a singular 

 fate. Answered at certain epochs by an almost unanimous negative, it 

 has emerged again with exery fresh advance in mechanical, physical 

 or chemical knowledge, and for a time has seemed about to be settled 

 in the affirmative. It was so in the seventeenth century when the dis- 

 coveries of the new geometry and the new mechanics were hailed by 

 Descartes and the iatro-mathematical school who were his lineal descend- 

 ants, although they denied their parentage, as the key which was 

 to unlock all the secrets of that cunningly devised automaton, the 

 animal body, and particularly to explain its movements. At a later 

 date, the determination of the laws of the diffusion of gases appeared 

 to solve the problem of the passage of gases through the lungs, and 

 the determination of the laws of diffusion of dissolved substances and 

 of endosmosis, the problem of absorption from the intestines. With 

 Ludwig's researches on the formation of urine, secretion seemed about 

 to pass out of the group of mysterious 'vital' phenomena, and to become 

 a mere process of filtration. But always as renewed investigation has 

 brought into clearer light the peculiarities, the wizard tricks, one might 

 almost say, of those rare mechanisms that ply so deftly even in the 

 common business of the bodily machine, the gulf that separates the 

 inorganic from the organized world has opened wide as ever, and physi- 

 ology has still had to wait for a new Curtius to close it. 



Quite recently the experiments of de Vries, Van't Hoff and others 

 on osmosis have supplied further physical data for the solution of this 

 perennial problem, and have, therefore, become the starting point of 

 numerous physiological researches. Among these may be mentioned 



