CRITICISM OF BERT HOLD 299 



impossible to explain both the back currents and the 

 regular circulation of the protoplasm as a whole in a simple 

 Amoeba by means of such a spreading out at the anterior end, 

 and all the less since we have found that the theory 

 necessarily demands an exactly opposite current. 



Against the admissibility of the explanation which I 

 have put forth, Berthold finds an objection of great moment 

 in the fact which he claims to have established, namely, 

 that in the water surrounding an Amoeba, after mixing 

 carmine with it, no system of currents was to be observed 

 at its anterior end such as is required by the explanation. 

 With reference to this point I may remark that I regard 

 the observation of such currents as very difficult, when the 

 extent, for the most part very slight, of the currents of 

 Amoebse is taken into consideration, and that, therefore, 

 in the meanwhile, I still regard their presence as possible. 

 Unfortunately I have hitherto delayed inquiring into this 

 question myself.^ Yet I may refer to an observation which 

 shows that the apparent absence of currents in the surround- 

 ing water is not decisive with regard to the correctness of 

 the explanation. In small drops of oil, which were yet 

 considerably larger than most Amoebse, and which crept and 

 moved about very energetically under the influence of 

 surface tension, I could not demonstrate the existence of 

 currents of any kind in the surrounding water, with which 

 Indian ink had been mixed. This observation astonished 

 me very much at the time, since such currents are always 

 vei;y distinct and strong in the vicinity of large oil-drops. 

 Hence, without attempting to explain the reasons of this 

 deviation from the rule, it seems to me of sufficient 

 importance to diminish the difficulties raised by Berthold's 

 objections. 



If, however, we take our stand upon Berthold's hypo- 

 thesis, the complete absence of any phenomena of streaming 

 in the surrounding water would be just as strong evidence 

 against his explanation as against that put forward here. 

 Since Berthold's hypothesis is founded exclusively upon 

 the alterations of surface tension which are caused by 



^ See Appendix at the end of the next section (pp. 317-319 infra). 



