48 



PROTOPLASM 



gressive movements are without doubt in connection with 

 such streamings, although no definite conclusion on this 

 point can be obtained in the opaque drops. 



To obviate any possible objection that pressing the 

 cover glass or anything of the sort may cause the move- 

 ments of the drops, I remark especially, that experiments 

 were also carried out with perfectly firmly fixed cover glasses, 

 which rested on strips of glass fastened with paraffin, and 

 that just the same results were then obtained. 



If the water be slowly replaced under the cover glass by 

 semi-dilute glycerine, a system of very energetic circulating 

 currents is gradually set up in most drops, such as has 

 briefly been mentioned earlier for certain oil-drops (see Fig. 

 5). Thus, from the upper edge of the drop, which is in 



contact with the cover-slip (D), as well as from the lower 

 edge, which lies on the slide (0), a superficial current, 

 streaming out on every side, travels towards the equator (a), 

 where the two streams unite and now pass inwards as a 

 common stream towards the centre of the drop ; from this 

 spot the centripetal stream bends upwards and downwards 

 into the two currents first mentioned. It may be observed, 

 however, in drops displaying such a streaming motion, that 

 frequently streams suddenly start here and there from the 

 interior towards the free edge, and disturb the circulation 

 described, though it usually soon regains the upper hand. 

 Small drops, however, which rest on the floor of the slide, 

 not infrequently show from the first another mode of 

 streaming, viz. an axial stream passes out from their in- 

 terior towards a point of the equator, spreads out here on 

 every side, and rushes along in the superficial regions towards 

 the hindmost point, where it gradually bends round again 

 into the axial forward stream. The mode of streaming last 



