26 PROTOPLASM 



it is possible, by lowering and raising the tube, to 

 determine clearly the same state of things in the finest 

 meshes (see Photogr. I. and II.) I lay special stress on 

 this because, as we shall see later, pictures of a fine network 

 can also be produced by the microscope as optical delusions 

 when small, strongly refractile granules or spherules are in 

 close apposition to one another. On this account I must 

 at once lay emphasis on the fact that, as a rule, I failed to 

 demonstrate the presence of strongly refracting granules 

 or spherules of a solid nature in the froths, even with 

 polarised light, by which they appear perfectly dark when 

 the prisms are crossed. 



The optical relations, just described, of the meshes or 

 alveolar spaces of the froths, are also definite evidence against 

 the assumption of a net-like or spongy structure, if such an 

 assumption still required any refutation after all that has 

 been stated. But since, however, it is a question of such 

 extremely fine microscopical relations, that the determination 

 is so difficult in many ways, attention may be drawn here 

 to yet another circumstance. We shall see later, that the 

 frothfi under the influence of induction shocks show distinct 

 bursting of their alveoli ; a similar effect can be also pro- 

 duced by the addition of certain fluids. It is possible to 

 follow out the way in which neighbouring froth vesicles 

 or alveoli suddenly burst into one another, exactly as they 

 do in macroscopic froths. When superficially-placed froth 

 vesicles suddenly burst to the exterior, the very small drops 

 of froth take on jerky, springing movements, which is easily 

 explained by the fact, that at the spot where such a vesicle 

 bursts the surface tension is suddenly very much decreased. 

 As a result of this the stronger pressure of the remaining 

 surface impels the whole drop of froth for a short distance 

 forwards in the direction of the radius passing through the 

 spot on the surface at which the vesicle burst. 



In the investigation of the fine froths the attention is at 

 once arrested by the fact that the nodal points in which the 

 edges 1 of three alveoli meet one another are always dis- 



1 I speak here and in the sequel of the edges of alveoli, being indifferent as 

 to whether sections of lamellae or actual edges are to be understood thereby, 



