CELLS AND TISSUES. 27 



must be able to take place within the cell and often with 

 great velocity. 



In those cases in which changes in the shape of the 

 protoplasm under investigation can be easily explained 

 through the assumption of the existence of a surface 

 tension, there seems to be no reason for doubting the 

 fluid nature of the protoplasm, for surface tension is 

 ordinarily looked upon as a dependable criterion of the 

 liquid state. The amoeba, which becomes spherical in 

 a state of rest or when universally excited, or forms 

 pseudopodia when it suffers a local alteration in surface 

 tension, may be looked upon as a liquid mass as long as 

 it has ot been possible to demonstrate in it a noticeable 

 displacement elasticity such as torsion. To prove the 

 existence of the latter by suitable experiment has never 

 been attempted, so far as I know. Since the discovery 

 of the "amoeboid" movements of oil droplets and the 

 careful physical analysis of this phenomenon by QUINCKE, 

 the formation of pseudopodia has been robbed of the 

 characteristics of a specific life phenomenon, and later 

 investigators have shown that it is governed in all its 

 details by the laws of surface tension. The taking up of 

 food and the process of defecation in rhizopods can 

 also be easily explained in this way. RHUMBLER could 

 even imitate most cleverly with drops of chloroform and 

 threads of shellac such apparently complicated phenomena 

 as the rolling up of algae threads within the body of 

 Amceba verrucosa. By similar methods he was able to 

 imitate in a most surprising way the formation of cases 

 about testaceans by rubbing up fine quartz or glass pow- 

 der with different kinds of oils or chloroform, and 

 dusting this into dilute alcohol or water. E. ALBRECHT, 



