34 NATURAL SCIENCE. Jan., 
point of contact. As it passes round it gets more and more diluted, 
and the equilibrium continues to be disturbed. The surrounding 
fluid presses in to replace the soap solution, which is carried back- 
wards from the point of contact, and this general pressure, acting 
alike on oil, soap, and water, moves up the oil drop slowly towards 
the point of contact with the soap solution. 









Fic. 3.—Soap solution (seife) in contact with drop of oil (o/) suspended in water, 
showing streaming movements. 
In the actual case of the froths, the soap solution is contained in 
the cells of which the froth is composed. Centres of streaming move- 
ments are produced by the soap solution diffusing out into the sur- 
rounding liquid or by the bursting of superficial cells. 


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Fic. 4.—Foam ot olive oil and carbonate of potassium, very viscous, much magnified. and 
pressed into fibrils by the cover glass. The upper figure is a higher magnification of 
part of the lower figure. 
From a consideration of these froths Professor Biitschli passes to the 
observed appearances of actual protoplasm in the animal and vegetable 
kingdom, and from alargenumber of instances collected from all manner 
of cells, he shows how readily these appearances can be interpreted 
if we suppose protoplasm to have a frothy structure like the structure 
of his artificial drops. Of these two instances are reproduced opposite. 
