VACUOLES 227 



(/>) Vacuolcs 



To these certain facts belongs, in the first place, the gene- 

 ral formation of racttolcs. There is no need of any special 

 proof that vacuoles are drops of fluid in view of the universal 

 agreement which prevails upon this point. On the other 

 hand, observation teaches, in the plainest manner, that every 

 vacuole is completely shut off by a delicate, somewhat darker, 

 and rather shiny border, which is exactly similar to the 

 external pellicle-like border of a naked protoplasmic body. 

 It is, in fact, notorious that the existence of a special vacuolar 

 membrane has been asserted again and again, without, how- 

 ever, any sure proof having been brought forward for the 

 fact. The adherents of the theory of a spongy framework in 



or viscidity of the margin, adhesion can alone be regarded as the cause of the 

 phenomenon. As we have already discussed before (p. 37 above), the margin 

 of such an adherent foam-drop is exceedingly attenuated, for which reason it 

 seems quite possible that it is hindered in its streaming movements throughout 

 its entire mass in consequence of the adhesion. If this conclusion is the 

 correct one, it would follow definitely from it that protoplasm, when viscid 

 throughout its entire mass, must always possess a very thin quiescent marginal 

 layer, as long as it adheres to a solid cell membrane. Such a result, however, 

 if correct, of course does not in any way exclude the fact of the external layer 

 also possessing, in part, an actually heightened cohesion, especially after the 

 protoplasm has become detached from the cell membrane by plasmolysis, and 

 is also surrounded externally by a watery solution. 



On the ground of his view as to the viscid nature of protoplasm Pfeffer then 

 expresses the following opinion "that ... in no case is a firm, continuous, 

 permanently rigid framework admissible in protoplasm." My experience has 

 also led to the same conclusion, while in our views upon the structural rela- 

 tions of protoplasm we differ very essentially from one another. The very 

 brief remarks made by Pfeffer in 1890 (p. 255, footnote) upon this point are 

 not very clear, and cannot in any case serve as an explanation of the struc- 

 tures often so distinctly observed even in living protoplasm. He says : 

 "Possibly parts of the cytoplasm are differentiated in a retrograde manner, 

 and it is even probable that within the cytoplasm parts of unequal cohesion 

 and density are formed, which under certain circumstances are capable of 

 being optically observed either directly or in fixed preparations. I suppose 

 that in such a manner, and necessarily also with the co-operation of a different 

 distribution in space of the microsomes, etc., a portion of the structural rela- 

 tions in question hitherto observed comes to be formed." Only from the 

 circumstance that Pfeffer never occupied himself thoroughly with the investi- 

 gation of protoplasmic structures am I able to comprehend to some extent how 

 he could let fall an opinion of this kind upon these matters, which are part 

 of the fundamental details of the protoplasm question. 



