898 



SCIENCE. 



[N. S. Vol. II. No. 52. 



to contact with a third liquid which has a lower 

 surface tension than the second liquid. Thus, 

 if a drop of oil in water be brought into contact 

 with weak alkali active currents are set up in 

 the water and in the oil. Now, as the foam is 

 a framework of very minute lamellae of oil, the 

 meshes of which are filled with a watery liquid 

 containing potassium carbonate and potash soap, 

 Ave have the conditions necessary for the forma- 

 tion of extension currents and streamings if al- 

 veoli burst at the surface and readjustments are 

 made throughout the mass by the aid of diiTu- 

 sion currents and the bursting of internal al- 

 veoli. 



Whatever the true cause of these movements 

 in the foams their appearance is such as to sug- 

 gest some of the movements of an amoeba and 

 it becomes pertinent to inquire if certain proto- 

 plasmic movements may not be the direct phys- 

 ical result of their assumed alveolar or foam 

 structure. The movements of protoplasm are 

 commonly spoken of as due to its contractility, 

 and in an Amoeba this contractility has been 

 thought to be located either in the ectosare or 

 in an internal framework. Many, however, have 

 called attention to the fact that the movements 

 of an Amoeba and the streamings in a plant cell 

 could not be explained upon any assumed 

 contractility in an internal framework. Hof- 

 meister referred movements of protoplasm to 

 changes in power of imbibition and Sachs elab- 

 orated a similar idea. Englemann in 1879 as- 

 sumed that his minute theoretical particles of 

 protoplasm, inotagmas, changing their state of 

 turgidity passed ft-om an elongated to a spher- 

 ical form and thus brought about contraction of 

 protoplasm. As late as 1879 older views as to 

 the participation of electrical forces in proto- 

 plasmic contraction reappeared in the papers of 

 Felton and of Fol. Leydig, 1885, and others 

 since then have regarded the hyaloplasma, and 

 not the framework, as the essential motile sub- 

 stance. 



Surface tension as an element in protoplasmic 

 movements was brought in by Berthold, in 1886, 

 in explaining the streamings in plant cells; 

 while Quincke, in 1888, explained such move- 

 ments on the basis of extension currents caused 

 by surface tension. Though Quincke's concep- 

 tion of the structure of the plant cell was quite 



unlike what has been observed his application 

 of surface tension and of extension currents 

 served as an introduction for Biitschli's explana- 

 tion of protoplasmic movements. 



Professor Biitschli attempts to explain some 

 of the more simple forms of amoeboid move- 

 ment as results of the foam-like structure 

 of protoplasm, and thinks surface tension and 

 extension currents are the essential factors. 

 The axial stream which is found in many Amoe- 

 bse passing towards the progressing anterior 

 end to bend and flow back near the surface of 

 the animal is, lie thinks, an extension current. 

 The chief difierences that he sees between such 

 axial streams and the extension currents in arti- 

 ficial foam is that they endure but a short time 

 and flow back but a short distance in the Am- 

 oeba. The conditions present in protoplasm 

 may be such as to form extension currents, for, 

 as we assume it to be a fi-amework of liquid not 

 soluble in water enclosing water containing 

 substances in solution, we may suppose changes 

 in surface tension would set up such currents as 

 they do in the manufactured foam drops. There 

 is some evidence that the watery parts of proto- 

 plasm are alkaline and it is also probable that 

 fatty compounds may be present in the frame- 

 work. The bursting of some alveoli at the sur- 

 face would pour out on to the surface some of 

 the watery contents which will cause a local 

 diminution in surface tension and thus give rise 

 to an extension current. In this way, also, 

 pseudopodia may be formed, here and there, 

 by local extension currents. 



This explanation, however, cannot be applied 

 to the formation of the remarkable anastomos- 

 ing pseudopodia of many Ehizopods, and even 

 where it seems to apply it meets with a severe 

 rebufi' in the results of experiments upon Pelo- 

 myxa. It was found that India ink in the 

 water about a crawling Pelomyxa shows cur- 

 rents the reverse of what they are about a drop 

 of licjuid exhibiting extension currents, so that 

 the assumption of this simple physical explana- 

 tion for the movements in an Amoeba seems on 

 a very weak footing. 



The author, however, thinks that in some 

 way the extension current may perhaps be ap- 

 plied to the explanation of rotation movements 

 in the protoplasm of plants cells, and that even 



