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. 



Fig. 3. — Soap solution (scife) 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. 



Fig. 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 thesefroths Professor Biitschli passes to the 

 observed appearances of actual protoplasm in the animal and vegetable 

 kingdom, and from a large number 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. 



