92 THE MECHANISM Ol~ ABSORPTION AND TRANSLOCATIOX 



plasmatic elements. If the diosmosing substances do actually penetrate 

 the structural plasmatic elements and are transmitted by them, then 

 the model would have to be altered by filling the space between the 

 two membranes with a mass of gelatinous substance, through which the 

 diosmosing salt must penetrate, in order to pass from the one membrane 

 to the other. In both cases, however, the general principles are similar, 

 for in the latter, as in the plasma, we have to deal with a spongy 

 framework impregnated with water, through which soluble crystalloids 

 diffuse with the same rapidity as they do in water 1 . Even though the 

 transmission of a diosmosing substance through the mass of the plasma 

 were mainly due to diosmosis, nevertheless the distances to be tra- 

 versed are very small, and more or less pronounced movements of the 

 plasma may accelerate the transference of substance from one part to 

 another. 



Many soluble crystalloid substances cannot diffuse through plasmatic 

 membranes, and hence the elements or micellae of which the latter are 

 composed must be closely associated together, leaving relatively narrow 

 miccllar interstices, and this conclusion necessarily holds good, whatever 

 the substance or structure of the plasmatic membrane may be. Like 

 the rest of the protoplast, the membranes which cover it are of a viscous 

 consistency, and may be stretched considerably without being ruptured. 

 For diosmosis, i.e. for diffusion through a separating membrane 2 , it 

 is immaterial whether the membranes in question are solid or fluid in 

 nature, and all the essential characteristics of imbibition and diosmosis 

 are fulfilled even when a substance diosmoses merely because it is soluble 

 in the substance of the separating membrane. 



The cell is therefore an osmotic system, composed of a series of 

 membranes, one outside the other; the outermost, or cell-wall, affording 

 rigidity to the whole, and permitting the existence of powerful internal 

 osmotic pressure, which would otherwise unavoidably rupture a body of 

 such feeble consistency and rigidity as the naked protoplast. 



The diosmosis of crystalloids through this system is of similar character 

 to that through an animal membrane such as the wall of the bladder. 

 Most soluble substances readily diosmose through the cell-wall, but many 

 crystalloids are unable to diffuse through the plasmatic membranes, or 

 to penetrate to the plasma. The greater permeability of the cell-wall 

 is shown by the fact, that substances dissolved in the cell-sap pass outwards 

 as soon as the plasma is killed. Thus the water, in which cherries or 

 clean slices of beetroot are boiled, only becomes red, when the high 



1 Voigtlander, Zeitschr. f. physik. Chemie, 1889, Hd. Ill, p. 316. The first experiments on 

 Osmosis were performed by Graham, 1862. Later literature by Voigtlander. See Ostwald, Allgem. 

 Chemie, 1891, 2. Aufl., Bd. v, p. 687. 



3 See \Yinkelinann, Handb. d. Physik, iSyi, 1x1. I, p. 618. 



