IV] 



STRUCTURE OF THE CELL 



171 



mesh work (often described, from its appearance in optical section, 

 as a "reticulum"), consisting of more solid substances, with more 

 fluid matter filling up the interalveolar meshes. This phenomenon 

 is nothing else than what we call in ordinary language, a "froth"' 

 or a "foam." It is a surface-tension phenomenon, due to the 

 interacting surface-tensions of two intermixed fluids, not very 

 different in density, as they strive to separate. Of precisely the 

 same kind (as Biitschli was the first to shew) are the minute alveolar 

 networks which are to be discerned in the cytoplasm of the cell*, 

 and which we now know to be not inherent in the nature of 



Fig. 42. 



Fig. 43. 



protoplasm, or of living matter in general, but to be due to various 

 causes, natural as well as artificial. The microscopic honeycomb 

 structure of cast metal under various conditions of cooling, even 

 on a grand scale the columnar structure of basaltic rock, is an 

 example of the same surface-tension phenomenon. 



* Arrhenius, in describing a typical colloid precipitate, does so in terms that 

 are very closely applicable to the ordinary microscopic appearance of the protojjlasm 

 of the cell. The precipitate consists, he says, "en un reseau d'mie substance 

 solide contenant peu d'eau, dans les mailles duquel est inclus un fluide contenant 

 un peu.de coUoide dans beaucoup d'eau. ..Evidemment cette structure se forme 

 a cause de la petite difference de poids specifique des deux phases, et de la con- 

 sistance gluante des particules separees. qui s'attachent en forme de reseau." Rev. 

 Scientifique, Feb. 1911. 



