PROTOPLASMIC STRUCTURE 77 



the same kind, a process suggesting an irreversible 

 type of adsorption. A few examples of irreversible 

 adsorption may be cited for illustration. Freundlich 

 and Losev^ found that a solution of the dye, crystal 

 violet, was completely decolorized by animal charcoal, 

 and that washing would not give back the dye. This 

 may mean that the concentration of the dye in solution 

 at equilibrium is indefinitely small; but more probably 

 it points to the formation of an insoluble modification 

 as the result of adsorption. Proteins like egg-albumin 

 when adsorbed at the surface of drops of chloroform, 

 form thin highly insoluble and resistant pellicles; i.e., 

 the protein undergoes the change usually described as 

 "denaturation." Various other cases of anomalous 

 adsorption are probably to be referred to conditions of a 

 similar kind; the adsorbed material apparently under- 

 goes some chemical modification. 



A further fact of fundamental biological interest is 

 that the adsorbent action of many materials has a 

 certain specificity or selective character; i.e., the action 

 varies from adsorbent to adsorbent independently of 

 the latter's state of subdivision. This phenomenon has 

 apparently the same ultimate basis as have the specific 

 chemical affinities between substances; in fact, the 

 distinction between adsorption and the formation of 

 true chemical compounds is now very generally recog- 

 nized as ill defined.^ The phenomena of cohesion, adhe- 

 sion, and capillarity are closely related to adsorption; 

 thus water wets (is adsorbed by) certain solid surfaces, 



' Freundlich and Losev, Z. physik. Chem., XLIX (1907), 284. 



* Cf. Langmuir, op. ciL, pp. 1900 fif.; also Journal of the American 

 Chemical Society, XL (191 8), 1361. 



