CHAP, vni THE GENERAL PHYSICAL PROPERTIES OF ALBUMINS 253 



especially suited for demonstrating the transition from colloids 

 into crystalloids, for some of them exhibit all the properties of 

 colloids and yet crystallise ; crystalline egg-albumin, judging by the 

 ' gold-number ' of Schulz and Zsigmondy, 1 occupies a position inter- 

 mediate between colloids and crystalloids. Casein and the mucins 

 cannot be coagulated like the ordinary albumins, but they change 

 their physical characteristics on being 'denaturalised/ and amongst 

 albumoses are found all transitions between hetero-albumose, on the 

 one hand, which does not diffuse in neutral and only very slowly in 

 acid and alkaline solutions, and between peptones, which diffuse readily, 

 on the other hand. What factors we are dealing with in colloidal 

 solutions we do not know. Hofmeister 2 believes the two chief 

 characteristics of colloids to be their great tendency (1) to become 

 insoluble under the slightest non-chemical provocations, as e.g. on 

 slight evaporation of the water in which they are dissolved, or on 

 coming in contact with porous substances, and (2) to form exceedingly 

 thin membranes or particles, which have the power of swelling up on 

 being moistened, provided they have been dried previously. He 

 attributes to this behaviour of colloids the great difficulties we 

 experience in working with albumins, particularly when we endeavour 

 to prepare them in a pure state. Owing to these very same pro- 

 perties, albumin possesses in a higher degree than does any other 

 substance the power of forming tissues, and protoplasm with its 

 peculiar semi-fluid structure. 



As in the case of other colloids, so in the case of albuminous 

 substances it is easy to rob them of their peculiarities, and once 

 albumins have changed it becomes impossible to restore them ; the 

 process is irreversible, and the changed albumin is said to be 

 denaturalised or coagulated. The dissociation -products and deriva- 

 tives of albumins, namely, the albumoses, peptones, halogen-albuminates, 

 methylene-albumins, etc., are no longer colloids, and can therefore not 

 be denaturalised. 3 It is characteristic of the natural or real albuminous 

 bodies, or the albumins proper, that they become permanently de- 

 naturalised, and that they cannot be rendered soluble again without 

 extensive dissociation or other change of their original state, if once 

 they have been coagulated by heat or some other process. 



1 F. Schulz and R. Zsigmondy, Hofmeister s Beitr. 3. 137 (1902). 



2 F. Hofmeister, Zeitschr. f. physiol. Chem. 14. 165 (1889). 

 3 That the author does not agree -with these views will become apparent later. 



