FOAM STRUCTURES IN COLLOIDS 217 



is acquainted with the optical appearance of finely frothy- 

 structures, and has more especially become sufficiently an 

 expert by the study of coarser foam structures. On the other 

 hand, great difficulties may be presented by the question as to 

 what conclusions are really to be drawn from these results. 

 Those who, like Berthold, Schwarz, and KoUiker, deny generally 

 the existence of structures in living protoplasm, will of course 

 be inclined to look upon the above results simply as a confirma- 

 tion of their view that the alleged structures only owe their 

 origin to processes of coagulation of this kind. In answer to 

 this I must declare afresh that their opinion is untenable in view 

 of the numerous cases in which the structures are distinctly 

 demonstrable in living protoplasm. Only for such protoplasm, 

 as in life appears quite hyaline, would their interpretation of 

 the structures which appear in the fixed condition be possible. 

 But it should first be decided with sufiicient clearness what 

 significance properly attaches to these foam structures of 

 coagulated white of egg and gelatine. The subject still lies in 

 obscurity. Two opposite possibilities confront one another here. 

 Either fluid albumen and watery gelatine are homogeneous 

 bodies in the sense of a solution, and at the moment of coagula- 

 tion undergo a process of desolution with formation of froth, just 

 as we have above become acquainted with an instantaneous forma- 

 tion of foam in suitable oil-drops ; or these bodies are not homo- 

 geneous in the sense of solutions in the uncoagulated condition, 

 but are very fine foam structures, of which the two components 

 possess such similar powers of refraction that their structure is 

 not recognisable. , The frothy structure of their coagulation 

 products would, in this case, not be a new formation, but it 

 would merely be a case of their being rendered distinct, owing 

 to the frothy framework undergoing an alteration, that is to say, 

 becoming strongly refractile, and hence distinctly visible. Which 

 of these two possibilities is the correct one, it is impossible to 

 decide off'-hand. 



On the whole, I am more inclined, at the present time, to the 

 latter view, without, however, being able to prove it satisfactorily, 

 or to overcome certain difiiculties which stand in the way of the 

 assumption that it is correct. 



The following points are, in my opinion, in favour of the 

 assumption. As I have already pointed out, a layer of radiate 

 alveoli can be observed plainly in .coagulated albumen and 

 coagulated gelatine. The gelatine was not brought into the 

 coagulating fluid until it had stifiened to a jelly. Now, since the 

 formation of a typical radiate alveolar layer is connected with 

 the fluid aggregate condition, the development of such a layer in 



