CHAPTER XI 



THE INFLUENCE OF THE ORGANS ON ONE ANOTHER 



ALTHOUGH the individual organs, and indeed the individual cells of the 

 Metazoa, carry on their life to a certain extent independently, they are in 

 many ways dependent on one another. In truth it is only by this mutual 

 relationship that the activity of the numberless minute parts can result in 

 the life of the whole body. 



This interdependence of the individual parts of the body is made effective 

 primarily through the nervous system. There occur, however, between the 

 separate organs many reciprocal influences more or less independent of the 

 nervous system, which are of very great importance for the functions of the 

 body and which participate largely in the regulation of its mechanisms. Here 

 belong osmotic processes brought about by alterations in the cells or in the 

 lymph, and the influence which different organs exercise on one another by 

 means of products formed in them and delivered to the liquids of the body. 



1. THE OSMOTIC PHENOMENA 



All the cells of the body are permeable to water, although some of them 

 are permeable only in one direction. If salts were neither added to nor lost 

 from the body, in time, by the absorption and elimination of water, the same 

 osmotic pressure would come to prevail not only in all the cells, but throughout 

 all free liquids of the body. After the exchange between water and the ultimate 

 particles of salts had ended, an equilibrium would everywhere be established 

 between the contents of the cells and the liquid bathing the cell. 



This condition of absolute equilibrium of osmotic pressure within the whole 

 organism would cease however, and in fact would cease all at once for the entire 

 system, the instant the osmotic pressure at any one place were changed by the 

 solution or by the deposition of new molecules. If the osmotic pressure in a 

 cell be raised by an increase in the number of molecules dissolved in it, the 

 following phenomena may ensue: (1) if the cell walls are perfectly permeable to 

 salt molecules, the latter in their endeavor to diffuse uniformly will wander 

 out of the cell i. e., will betake themselves from a place of higher concentration 

 to a place of lower until equilibrium again prevails everywhere; (2) if the cell 

 wall is impermeable to these molecules, then in their endeavor to diffuse they 

 will exert a pressure upon the wall, and water will pass from the surrounding 

 medium into the cell. In this way the liquid in the immediate neighborhood 

 of the cell becomes more concentrated and now acts in turn to draw water toward 

 the periphery of the cell. The movement of water thus set up continues until 

 the difference of pressure becomes too small to be effective. A third case still 

 is conceivable, namely that the cell wall is not absolutely permeable to the salt 



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