COLLOIDS 63 



any of the dispersion medium in A, it will require a pressure sufficient to 

 cause the more fluid phase to penetrate the more solid. If the gel is 

 treated with reagents like formaldehyde, the liquid can be readily pressed 

 out. This occurs during fixation for histological purposes. 



Imbibition 



Closely related to gel formation is the process of imbibition the 

 power of taking up large quantities of water without actually forming 

 liquid solutions. Besides gelatin the dried tissues pf plants and animals 

 exhibit the phenomenon, and it is undoubtedly of importance in many 

 physiological processes such as growth and the passage of water into 

 cells, etc. The materials present as vacuoles in plant cells attract water 

 from the environment of the cell by imbibition, and thus exert on the 

 cell wall a pressure which, acting along with the osmotic pressure, 

 maintains the turgor of the cell. The initial growth of pollen is also 

 dependent upon imbibition, and important observations on this process., 

 under varying conditions, are likely to furnish us with useful informa- 

 tion concerning the significance of imbibition in connection with growth 

 of cells in general. 



By measuring the rate of increase in length of long, narrow strips of gelatin placed 

 in Petri dishes containing solutions of varying composition, the factors that influence 

 the imbibition process can be quantitatively investigated. Working in this way, F. H. 

 Lloyd" has found that for all acids there is a certain concentration (about N/320 

 H 2 S0 4 ) which induces a maximum rate of swelling, and another, much weaker (N/2800 

 H 2 SO 4 ), in which the rate of swelling is even less than in pure water. In higher con- 

 centrations of acid than N/320, the gelatin at first swells very quickly; but the rate 

 slows off so that it soon comes to be less than that with intermediate concentrations. 

 Regarding alkalies, at high concentrations the effect is similar to that of acids. Salts 

 alone seem to repress the swelling below that of water. It should be pointed out 

 that the concentrations of acid and alkali in the above observations are much greater 

 than those that could occur in the animal body. The experiments recall the attempts 

 made some years ago by Martin Fischer to explain edema as due to excessive imbibition 

 of water by the proteins of the tissues because of increased acidity of the blood and 

 tissue fluids. That imbibition might possibly play some role in such processes is not 

 denied, but Fischer disregards entirely the now well-established facts that hydrogen- 

 ion concentration is one of the most constant properties of the blood, that very low 

 concentrations of acid may diminish rather than increase imbibition, and that it is 

 manifested only in the absence of inorganic salts.* Moreover, the fluid in edema can 

 often be drained off by hollow needles, and it passes by gravity from one part of 

 the body to another, neither of which processes would be possible if imbibition were 

 the essential factor concerned. If further evidence against this hypothesis should be 

 demanded, it might be found in the utter failure of the therapeutic measures alkali 

 administration that are recommended to combat the edema. 



Action of Electrolytes on Colloids (apart from their effect on osmotic 

 pressure). It has been stated above that the charge which a colloidal 



*Determinations of the hydrogen-ion concentration of the blood recently published from Fischer's 

 laboratory do not inspire confidence. 



