ioo PRINCIPLES OF GENERAL PHYSIOLOGY 



Most parts of plants and animals exhibit this property to a greater or less 

 degree. The stalk of the sea-weed, Laminaria, increases enormously in volume 

 under the conditions mentioned and has been made use of in surgical practice. 



The greater part of the experimental work on imbibition has been done on 

 gelatine, a considerable amount also on starch. 



Perhaps the most striking thing about the phenomenon is the great pressure 

 exerted in the process of swelling, or conversely, required to express water after 

 it has been taken up. Laminaria, under a pressure of 42 atmospheres, was found 

 by Reinke (1879) to be able still to take up 16 per cent, of water. 



In all these processes, it is important to remember that the total volume, gel 

 plus water, is less after swelling, although the volume of the gel itself increases 

 so much. In order to compress water to the extent implied in the total change 

 of volume, a pressure of some 300 atmospheres is necessary, so that it is plain that 

 heat must be evolved in the process of imbibition. 



This compression of water can be demonstrated in the following way, due to R. du Bois- 

 Reymond (1913). Pieces of the dried material, such as Laminaria, are attached to the 

 submerged part of a hydrometer, and the scale adjusted to a convenient point by addition 

 of weights. As the material swells, the hydrometer sinks, showing that the water which has 

 become part of the imbibition system has increased in density. Of course, the temperature 

 must be kept constant. 



Much work has been done on the effect of electrolytes on the swelling of 

 emulsoids, especially of proteins. The most striking effect is that of acid and 

 of alkali. Spiro (1904, p. 276) showed that either of these greatly increases the 

 amount of water taken up by gelatine, and Chiari (1911) found that, when carefully 

 purified, gelatine is sensitive to very small differences in H - ion concentration, so 

 that the difference between ordinary distilled water and that distilled out of 

 contact with carbon dioxide may be detected. The explanation of this pheno- 

 menon, as given by Pauli (1912, p. 262), is that electrolytically dissociated salts 

 of protein are formed by acid and by alkali, and the swelling is due to the atlinity 

 for water of the protein ion. This view will be discussed under the head of proteins. 



A theory of (edema has been propounded by Martin Fischer (1910) on the 

 basis of the action of acids on the swelling of proteins. The tissue colloids 

 are supposed to take up water under the influence of increased acid reaction 

 of the blood. Although the possibility of such effects must not be forgotten, 

 they will not easily explain the actual presence of liquid in dropsical tissues ; 

 a fine canula or hollow needle inserted into such tissues allows a slow stream of 

 fluid to drop from the end, and it is well known that oedema passes from one 

 part of the Ixxly to another in obedience to gravity. Moreover, so far as I 

 am aware, M. Fischer has not actually shown a change in FT ion concentra- 

 tion in the blood sufficiently large to account for the effect. As we shall see 

 in Chapter VII., the chemical composition of blood is such as to form an 

 extremely efficient arrangement for keeping the reaction constant. And again, 

 this delicate sensibility to change of H* ion concentration shown by gelatine is 

 only manifested in the absence of neutral salts, a condition not met with in 

 living organisms. 



The work of Siebeck (1912, p. 467) on kidney cells, and of Beutner (1913, 

 p. 224) on muscle, lead them to the conclusion that the increase of size, occurring 

 in certain solutions, is due to osmotic taking up of water, rather than to an 

 imbibition process, and that acid or alkaline reaction has no effect unless the 

 cells are permanently injured. Moreover, the action of neutral salts on the 

 volume of cells is in proportion to their molecular concentration only, whereas 

 the effect on imbibition is different according to the chemical nature of the 

 salt, even when in equi molecular concentrations. 



Hofmeister (1888), in fact, found the action of neutral salt* on the process 

 of imbibition to follow the same series as that already mentioned in the case of 

 "salting out." The relation of this series to the properties of the solvent has 

 been indicated on page 97 above. Samec (1911, p. 156) calls attention to the 

 fact that, parallel to the favouring effect exerted by the anions of the 

 Hofmeister series on the imbibition of water by starch, there runs a set of 



