236 COLLOIDS IN BIOLOGY AND MEDICINE 



The forces which accomplish the entrance of food into the organ- 

 ism and keep up the circulation of matter are in part purely mechani- 

 cal, as performed by the lungs, the heart, the peristalsis of the 

 intestines, etc. In addition to these, there are forces which ac- 

 complish chiefly the metabolism of the cells; the most important of 

 these are diffusion, osmotic pressure, swelling and shrinking. 1 



Circulation of Water. 



Until a few years ago the circulation of water in the organism was 

 chiefly attributed to osmosis. The vital processes constantly produce 

 from the colloids osmotically active crystalloids, which both retain the 

 water formed by oxidation and, in addition, attract water into the 

 cells, thus maintaining the turgor or normal tissue tension. This 

 presupposes that an almost semipermeable membrane surrounds 

 every cell. In the case of plants, this hypothesis offers certain 

 difficulties, and in the case of animals, it is impossible to maintain it. 



We shall present only a few examples which show that osmotic 

 conditions alone do not satisfactorily explain the distribution of 

 water in animal cells. 



Through the investigations of H. J. HAMBURGER, H. KOEPPE and 

 E. OVERTON, it is known that in the presence of alterations of 

 osmotic pressure, blood corpuscles and muscles change their volume 

 to much less an extent than would be expected of cells with fluid 

 contents and a semi-permeable membrane. Blood corpuscles contain 

 about 60 per cent water. In his experiment with osmosis, HAM- 

 BURGER showed that only from 40 to 50 per cent of their volume 

 could consist of an aqueous solution, so that from 10 to 20 per cent 

 of the water arises in some other way. According to OVERTON the 

 same thing holds for frog's muscle. 



Water is also retained by swelling. Swelling and shrinking are the 

 most powerful factors governing the circulation of water in the 

 organism. They may even act against osmotic pressure; nor are 

 we forced to explain their activity by any hypothetical membranes. 

 Changes in the reaction of the cells, especially the constantly recog- 

 nizable acid production during vital processes, give rise to the condi- 

 tions necessary for swelling or the circulation of water. With the 

 removal of the acids shrinking must occur again. 



M. H. FISCHER properly calls attention to the fact that a semi- 

 permeable membrane permitting the entry and exit of water from the 



1 J. TRAUBE* 1 regards the "surface pressure" as the force which causes the 

 movement of matter in the organism. Since there exists a certain parallelism 

 between the ability of many substances to lower surface tension and their capacity 

 to penetrate the cells, TRAUBE disregards the osmotic forces and lipoid solubility. 



