14 PROTOPLASM 



say if it is as good as that described below, or possesses 

 any special advantages. 



It is an interesting fact that white of egg exerts the same 

 influence as soap on the conversion of olive oil into froth. The 

 olive oil (a), used for the experiments hitherto described, was 

 allowed to stand some days over dried pulverised white of egg, 

 and then filtered off. Drops of this perfectly clear oil were brought 

 into water under the cover-slip in the way described. Numerous 

 extremely minute droplets of fluid appeared at once in the oil- 

 drop, which in a short time became turbid. Simultaneously it 

 took on the peculiar circulating streaming movements, described 

 below for drops of oil-foam in glycerine. A superficial current, 

 both from the upper and lower edges of the drop, streams out 

 radially from all sides, and runs towards its equator, where 

 the two streams coming from above and below meet, and pass 

 into a horizontal internal current, travelling from the equator 

 on all sides towards the centre of the drop. Here this in- 

 ternal current divides in all cases into an ascending and a de- 

 scending stream, which feed the two streards first described. 

 As shown later, this peculiar mode of circulation depends in 

 every case upon phenomena of extension which come into play 

 particularly at the upper and lower edges of the drop. Oil 

 treated in this way with white of egg becomes even after a few 

 hours totally turbid, and in places has a pronounced frothy 

 structure. Whether this effect upon the oil is due to the 

 white of egg itself, or whether it depends on a formation of 

 soap by the alkali in the white of egg, I leave undecided, though 

 the latter supposition seems to me the most probable. The 

 experiments described make it, however, very probable that the 

 conversion of the oil-drop into foam in the water depends on 

 its containing soap. Hence the extremely fine oil-foams pre- 

 pared as above described from drops of a thick mixture of oil 

 and common salt or cane sugar must also be considered from 

 this point of view. It is not the mere presence of small particles 

 of common salt or sugar in the drops that brings about the 

 formation of a foam, but the first origin of the fine droplets of 

 froth are rather to be referred to the soap naturally contained 

 in the oil. The fact that the formation of foam goes on much 

 more energetically and completely under these conditions may 

 be due partly to the sugar or salt in the oil producing a stronger 

 permeation of the oil by the water, and partly to the resulting 

 infiltration of the oil with numerous drops of salt or sugar 

 solution favouring the formation of the fine droplets of froth. 



