302 PROTOPLASM 



Since the currents, as has been said, go on exceedingly 

 energetically, the appearances to be observed in such drops 

 with slight magnification are particularly beautiful, and very 

 suitable to complete our knowledge gained in another 

 way with regard to streamings in oil-drops. The appear- 

 ance presented by an energetically streaming drop is in 

 general that represented in the preceding Fig. 19. One 

 recognises in it at once the two eddies (A) which we 

 have already found before, but in addition to these some 

 secondary eddies may also be observed (B and C), the 

 positions of which, and their relations to the principal 

 eddies, can be plainly made out from the figure, so that I 

 will not enter into a further explanation of them here. 

 One phenomenon, however, of particular interest, appears 

 between the two principal eddies, and is especially dis- 

 tinct when the latter are placed rather far apart in the 

 direction of their breadth. It can then be remarked that a 

 dark and rather broad band is stretched between them, which 

 depends on the fact that in the interval between the two 

 eddies another eddy corresponding to the thick band extends 

 througli the whole drop. Since this eddy is seen from 



above, it necessarily appears as a dark streak. This pheno- 

 menon is explained by the fact that in the whole breadth 

 of the drop the relations are essentially the same as are seen 

 on the two sides as it were in longitudinal section. A 

 median longitudinal section of the drop, of which a direct 

 view unfortunately is not to be obtained, would therefore 

 show something of 'the appearance represented in Fig. 20. 

 The sum of all the eddies which extend transversely through 

 the drop hence appears as the dark band. Since there is 

 a condition of relative quiescence in the interior of these 



