62 PHYSICOCHEMICAL BASIS OF PHYSIOLOGICAL PROCESSES 



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 of plants and animals 

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

 physiologic 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 composi- 

 tion, the factors that influence the imbibition process can be -quantita- 

 tively investigated. Working in this way, F. H. Lloyd 17 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 S0 4 ), in which the rate of swelling is even less than in pure 

 \vater. In higher concentrations 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 pro- 

 teins of the tissues because of increased acidity of the blood and tis- 

 sue fluids. That imbibition might possibly play some role in such 

 processes is not denied, but Fischer disregards entirely the now well-estab- 

 lished facts that hydrogen-ion concentration is one of the most constant 

 properties of the blood, that very low concentrations of acid may dimin- 

 ish rather than increase imbibition, and that it is manifested only in 

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



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

 laboratory do not inspire confidence. 



