50 PROTOPLASM 



briefly described the processes of streaming in a drop 

 of this kind, which moves forward with a single extension 

 centre, and the figures, which will be given in the sequel 

 of corresponding streamings in oil - drops, furnish a 

 sufficient explanation of it. One point, however, still 

 requires brief mention. It is frequently seen that the 

 hinder end of such a drop takes no further part in the 

 streaming, and is also marked out from the rest of the drop 

 by its somewhat different glassy appearance. Particles of 

 dirt, or of lamp-black which has been mixed with the 

 glycerine, collect at the hinder end, without in the main 

 changing their position. From this it follows, that at the 

 hinder end a condition of relative quiescence prevails, and 

 that this region takes relatively little share in the streamings. 

 Later on, when discussing the similar streaming movements, 

 which can be called forth in ordinary oil-drops, we shall go 

 more closely into the state of things observable at the 

 hinder end of the drops. 



Not infrequently a drop of the kind just described is 

 observed to run towards one of the strips of cover glass 

 employed as supports. Indeed, it would even seem as if any 

 drops in the neighbourhood of such a strip of glass have a 

 tendency to wander towards it. The drop then applies itself 

 more or less closely to the strip of glass, by the spot at 

 which the superficial streams spread out from a centre, and 

 continues to stream quietly, with, as it seemed to me, even 

 increased force. Such a drop, however, was never observed 

 to come free again from the glass strip of its own accord. 



It is even more curious when two drops run towards 

 one another. Neighbouring drops seem inclined to do this, 

 coming into contact with one another by the centres of 

 their extension - currents. The streaming then becomes 

 much stronger in both the drops ; this increase of strength 

 takes place, however, from reasons to be discussed later, even 

 before they directly touch one another. While the surfaces 

 of contact are visibly flattening out against one another, the 

 streaming is much intensified in both drops. It is note- 

 worthy how long a time passes before the drops flow 

 together all of a sudden. Although I took no accurate 



