46 PROTOPLASM 



The distinctness of this fibrous modification of the 

 alveolar structure in the froths described is naturally 

 only a consequence of the great viscidity of the substance 

 of their framework, which causes the meshes to persist 

 for a longer time in a state of tension. When the 

 framework is a more fluid substance, as in the ordinary oil- 

 lathers, a fibrous structure will also appear as the effect of 

 tension, but it will change again rapidly into the ordinary 

 condition. If, however, the action of tension remains persist- 

 ently in certain spots in the same direction, and the ground 

 substance is fairly fluid, fibrous structures will still possibly 

 come under observation. A case of this kind is that 

 formerly described in streaming froths, and we shall fre- 

 quently come across similar cases in the description of proto- 

 plasmic structures. It appears to me a point of a certain 

 degree of importance, that the froths described as having 

 a nearly firm framework show no marginal alveolar layer. 

 This fact appears to me quite intelligible, since the laws 

 which cause the formation of the marginal alveolar layer 

 only attain their full power under the condition that the 

 framework is a perfectly fluid substance. 



5. The Durability of the Oil-Foams 



The oil-foams can be kept for a relatively long time. 

 When put up in glycerine they show no noticeable change 

 for four to six weeks. Then, however, the froths gradually 

 deteriorate, slowly becoming coarser in structure through the 

 bursting of the alveoli. At last, also, homogeneous portions 

 of oil, no longer of a foam-like structure, appear in them. 

 I have not followed out more closely the process of degenera- 

 tion in the froths. 



We have, as yet, only studied the drops of foam under 

 the cover glass. If the cover glass be taken off, the drops 

 as such break up, since they are somewhat specifically 

 lighter than the surrounding fluid (H 2 or glycerine), and 

 hence ascend to its surface. Here they spread out into a 

 thin layer, which, sending out numerous irregular processes, 

 breaks up into small drops. In breaking up, however, the 



