22 PROTOPLASM 



parent. The larger drops require, as was said, clearing 

 up with glycerine. Although they then become very 

 transparent, it is nevertheless indispensable for the study 

 of their structure to compress them more or less strongly, 

 in order to be able to observe them in a very thin layer. 

 The thinner this is, the more clearly the structural relations 

 are shown. 



After clearing up with glycerine, the drops are seen to 

 be diminished very considerably in volume, just as is a 

 mass of protoplasm under the same conditions. This very 

 circumstance is, in my opinion, decisive in determining the 

 structural condition of such drops as foam-like, and not in 

 any way as bodies of a net-like or spongy structure. Since 

 the principal mass of the froths is oil, which is not itself 

 capable of swelling, the diminution of volume can only 

 depend on a process corresponding to the so-called plas- 

 molysis of plant cells. It can only be explained by the 

 fact that the mass of oil is honeycombed throughout by 

 numerous minute spaces quite closed off from the exterior, 

 and filled by a watery fluid, which, when subjected to 

 diffusion with glycerine, naturally give off more H^O to the 

 surrounding glycerine than it .takes up of the latter. The 

 consequence wiU be, therefore, a plasmolytic decrease of size 

 of the spaces filled with watery fluid, and hence, also, of the 

 whole drop. For further details on this point see below. 



As already mentioned, the microscopic investigation of 

 such froth-drops shows at once that, as a rule, they are more 

 or less abundantly filled throughout with larger drops of 

 fluid (vacuoles, up to "015 mm. in diameter). Very varying 

 relations are naturally met with in this respect ; occasionally 

 one obtains drops completely, or nearly completely, devoid of 

 the larger vacuoles, and which only consist of the finest 

 foam, while other drops are very full of vacuoles, so that 

 without closer investigation they appear to possess a coarsely 

 vesicular structure. Such froths often proved themselves 

 especially favourable for the phenomena of streaming. 

 The principal mass, which encloses the larger vacuoles, gives 

 the impression of an evenly and finely granular structure with 

 low magnification ; only when investigated with the best and 



