30 PROTOPLASM 



the oil-foams was not so easy to solve as it might have 

 originally seemed, on account of the fineness of the micro- 

 scopic structure, and since, in particular, it was difficult to 

 decide, by simple observation, whether it was possible for 

 granular deposits to make their appearance in consider- 

 able quantity in addition to froth vesicles, I took great 

 trouble in various ways to find out a method of reducing 

 the froths again to some extent. Since, as has been men- 

 tioned, strong induction shocks call forth continued bursting 

 of the froth vesicles, I tried if it would be possible to obtain 

 the desired effect by long-continued action of the inter- 

 mittent current. The result was, however, a negative one. 



Finally, chance led me, as is so frequent, the correct way. 

 If drops of foam, well washed out with water, be left to 

 stand undisturbed under the cover-slip without addition of- 

 glycerine, the water gradually evaporates, and the drop of 

 froth thus coming into contact with the air gradually loses 

 its frothy nature again completely. The water of the froth 

 vesicles slowly evaporates (or rather the latter burst, partly 

 from the contact of the air with the surface of the froth- 

 drop), and the soap left behind dissolves in the oil. Thus, 

 after some days the drops have again become as perfectly 

 clear and transparent as the oil originally employed for their 

 preparation. The smaller and the minutest drops then 

 show no trace of any deposits, even when viewed with 

 the strongest magnifications, while the large drops still 

 contain isolated small froth vesicles. Granular elements, 

 however, are either entirely wanting in the drops, or only 

 isolated granules are to be found, of medium size and 

 moderately strong refractile power. As has been said, when 

 they are present, they occur in such small quantity as not 

 to interfere in the least with the transparency of the drops. 

 Once I also saw fairly large clear crystals, approaching in 

 form to rhomboidal plates, together with needle-like crystals 

 in very limited quantity in the drops, as well as some gritty 

 bodies, which perhaps had arisen by strong compression 

 of such crystals. 



From these results it can hence be concluded with 

 complete certainty that solid deposits do not occur to any 



