SYMPOSIUM ON COLLOIDS 61 



the maintenance of supersaturation, or of a metastable equili- 

 brium. Likewise it seems to favor supercooling as does any 

 capillary system. This last feature of colloids is claimed to be 

 of importance in protecting the organism against death from 

 low temperatures (1 : pp. 50, 58, 27). The full discussion of 

 this point, pro and con, would lead us, however, too far away 

 from the main topic under consideration. A colloidal medium 

 then seems to favor these two "Uberschreitungserscheinun- 

 gen," supersaturation and supercooling, and perhaps through 

 these explain certain behavior of organisms. 



VI ENZYMES AS COLLOIDS 



Enzymes which play the main role in the metabolism of 

 living organism, have many characters indicating their col- 

 loidal nature. They are readily adsorbed by fine suspensions 

 or other colloids. This adsorption is probably due in part to 

 their surface tension activity, and in part to their electrical 

 characters. In the first instance they show themselves closely 

 related to the hydrophyllous colloids. In the second they mani- 

 fest weak suspensoid characters (2 : pp. 95-127). 



Even the strongest argument against their colloidal nature 

 — the fact that they never have been prepared in a pure state 

 and that we therefore do not know their true nature — is an ar- 

 gument favoring it also, for it is an outcome of high adsorp- 

 tion capacity. 



Griiss was able to separate the various enzymes of a plant 

 organ by placing a drop of its juice on a stretched filter paper. 

 As the drop spreads the enzymes arrange themselves in rings 

 about its center in order of ease of adsorption by the paper. 

 That the electrical charge of the enzyme particle is sometimes 

 a factor in its adsorption is shown by the following reactions : 

 kaolin, a negative suspension, will not adsorb invertase, a 

 negative colloid, but toncrt, a positive suspension, adsorbs in- 

 vertase readily. Kaolin will adsorb malt diastase only if the 

 diastase is acid in reaction, or is a positive colloid. In a neu- 

 tral medium malt diastase, like trypsin, pepsin, and ptyalin, is 

 nearly amphoteric, so the adsorption of all is more a matter of 

 surface tension. Filtering of enzymes through charcoal or re- 

 peatedly through filter paper lowers their activity due to ad- 

 sorption by the filter. The colloidal nature of enzymes has 

 been called into play as a means of explaining their re- 

 tention within the living cell. Hoffmeister believed 

 their colloidal character prevented them from dif- 

 fusing through membranes generally and especially through 



