REGENERATION or PROTOPLASMIC FRAGMENTS 507 



according to which the throwing out and the drawing in of 

 the pseudopodia are attributed to changes in surface tension. 

 This theory is based on the assumption that the pseudopodia 

 are liquid. 1 This assumption is a physical impossibility. 



The pseudopodia of Orbitolites are, according to the 

 drawings of Verworn, cylindrical ; their length perhaps a 

 hundred times greater than their circumference. Such a 

 liquid cylinder cannot exist. There is a good reason why 

 rain falls in drops and not in jets. If r is the radius, li the 

 height of a liquid cylinder, it can exist only as long as 

 h 2r7r. For this reason alone the entire contraction theory 

 of Verworn is wrong. I will not, however, discuss this theory 

 more closely here. 2 From these facts in surface tension it 

 follows that the pseudopodia of the Rhizopods cannot be 

 liquid, but must possess a solid framework or a solid mem- 

 brane. As soon as this solid framework or the solid membrane 

 becomes liquefied the pseudopods must obey the laws of 

 surface tension and break up into drops. The latter is, 

 according to my observations, the process which occurs in 

 fragments of Orbitolites which contain no nucleus. 



Is this liquefaction of solid substances a process which is 

 indicative of lack of oxygen ? This is undoubtedly the case. 

 Four years ago I showed that the cell-walls of the cleavage 

 cells of Ctenolabrus become liquid when deprived of oxygen. 

 When oxygen is readmitted, the formation of cell-walls 

 begins anew. 3 Budge tt showed in my laboratory that the 

 removal of oxygen leads to the solution of the cell- walls in 

 Infusoria also, and that certain poisons had the same effect. 4 

 Kuhne has observed the same effect of lack of oxygen. 5 The 



1 Die Bedeutung der lebendigen Substanz (Jena, 1892), p. 38. 



2 I do not here mention the chemotropic ideas of Verworn because they rest 

 upon no actual foundation whatsoever. 



3 "Investigations on the Physiological Effects of Lack of Oxygen," Part I, 

 p. 370. 



* American Journal of Physiology, Vol. I (1898). 

 a Zeitschr ift fur Biologic, Vol. XXXVI (1898), p. 472. 



