226 PROTOPLASM 



of the product of the fusion. If we add the numerous 

 observations made upon spherical vacuoles in protoplasm, 

 as well as the observations upon the fusion of threads of 

 protoplasm, and upon the drop-like shape which is assumed 

 by pieces of protoplasm which are isolated or set free from 

 their membrane ; and, finally, the condition of things in the 

 phenomena of streaming, it seems to me not possible to 

 doubt in any way the viscid or slow -flowing nature of 

 ordinary protoplasm. 1 



This conclusion will at once obtain further confirmation 

 when we are convinced that the assumption of a rigid 

 network in protoplasm agrees very little with certain facts, 

 or at least requires for its explanation complicated assump- 

 tions which render the supposition highly improbable. 



^Pfeffer also arrived, in 1890, at essentially the same conception of the 

 aggregate condition of protoplasm from similar grounds. Both the streaming 

 protoplasm of the Myxomycetes, and the principal mass of the protoplasm of 

 the vegetable cells enclosed in cell membranes, are regarded by him as "vis- 

 cous fluids," and although he frequently makes use of the term " plastic," he 

 particularly remarks that he only understands by it a condition differing in 

 degree from the viscid condition, i.e. one rather more coherent, and not in 

 any way a plastic condition like that of damp clay. Pfeffer, therefore, ex- 

 pressly recognises the fact that the chief mass of a protoplasmic body obeys 

 the laws of fluid substances, and if he is forced by his acquaintance with the 

 Myxomycetes to assume that their cortical layer possesses a greater cohesion, 

 or even solidity, that also the external layer of other protoplasts, as well as 

 cilia, are to be regarded as solid, yet our views agree completely in these 

 respects also (cf. on this point below, p. 240). As regards the cortical 

 layer of the Myxomycetes in particular, I can also only draw the conclusion 

 from Pfetfer's investigations that it possesses a considerably greater viscosity 

 than does streaming protoplasm, but that it is not, however, really solid, but 

 follows, although only very slowly, the laws of fluids. This conclusion can 

 be proved from the manner in which materials are taken up and given off from 

 the plasmodia, as well as from the easy transition from cortical substance to 

 the more fluid internal protoplasm. For the rest, I also consider it possible 

 that a portion of the observations which induce Pfeffer to ascribe a relatively 

 high cohesion to this cortical layer may depend on the fact that the plasmodia 

 of Myxomycetes adhere to the substratum, so that their extremely thin edges 

 have their mobility essentially diminished. In this connection I should like 

 to adduce certain observations upon streaming oil-drops which I have made 

 on occasions. If these drops, as sometimes happens, adhere firmly to the 

 slide, the very striking phenomenon might frequently be well seen of the 

 outermost edge of the froths remaining completely at rest, while streaming 

 movements went on in a very lively manner within this quiescent margin. 

 Since in this case there is no ground whatever for assuming a greater cohesion 



