GRANULES IN FOAMS AND PROTOPLASM 245 



froth-drops behave in this respect. When finely divided 

 lamp-black is mixed witli the oil from which the drops are 

 prepared, it may be noticed that in the drops of foam the 

 fine particles take up exactly the same position with rela- 

 tion to the foam, that is to say, that they lie in the nodal 

 points of the meshes. It follows from that, as would have 

 been supposed from the general relations of foam structure, 

 that the finest granules at least, if they possess a recognis- 

 able size, are forced into the nodal points. 1 Thus this 



1 I have subsequently found that Plateau (1882) has also made an observa- 

 tion which in like manner confirms the aggregation of solid granules in the 

 corners and nodal points of the alveoli of foam. If some spores of Ly co- 

 podium are scattered on a thin lamella of glycerine containing soap in solu- 

 tion, which is stretched out on a wire ring, and then the lamella is placed 

 under a bell-jar, the spores gradually all become carried towards the periphery 

 of the lamella, i.e. to the spot where it is fixed to the ring of wire. The 

 granules wander, therefore, as Plateau tried to prove, to the region where the 

 lamella is fastened to the ring by concave curvatures. Hence in a system 

 of lamellae the granules will collect at the edge, or at the nodal points, 

 where, as has been described before, the lamellae similarly pass into one 

 another with concave curvatures. With regard to the ultimate explanation 

 of the phenomenon the work of Plateau itself should be consulted. Since it 

 seemed to me of no small importance with reference to the protoplasm ques- 

 tion to obtain as certain a decision as possible of the question as to how solid 

 granules behave in macroscopic foams, I recently performed with this object 

 some experiments which easily and completely confirmed the supposition. 

 If a durable froth be made in a flask by blowing air by means of a glass tube 

 into a suitable fluid (soap solution mixed with glycerine or extract of soap- 

 wood), and at the same time there be mixed with the fluid not too small a 

 quantity of poppy-seeds or some other suitable fine-grained seed, the little 

 seed grains are taken up in great quantity into the framework of the soap 

 lamellae. By far the greatest number lie in the plainest manner at the nodal 

 points of the framework ; a smaller number at the edges, and only an occasional 

 seed grain is to be found perfectly isolated and contained free in a lamella. 

 Not infrequently also a nodal point contains a group of grains, or an edge 

 a series of them, one behind the other. When the bubbles burst it can be 

 plainly seen how the grains immediately travel back again to the nodal 

 points. These experiments with macroscopic foams confirm, therefore, as 

 has been stated, our hypothesis in the most definite manner. If some 

 rubbed-down carmine be taken instead of seed grains, one finds the same 

 relation in respect to the coarser grains. It is interesting to note, how- 

 ever, that the finest carmine granules also collect by preference at the 

 nodal points, so that the latter appear red, while the edges and lamellae are 

 colourless. All these observations present a certain interest, since they show 

 us that the nodal points of the framework may appear darker or show other 

 peculiar relations under certain conditions, even without larger or recognis- 

 able granules being lodged in them. For in protoplasm it may also happen, 



