224 PROTOPLASM 



represent to themselves the filaments or the network as com- 

 posed of a firm substance. When the fundamental laws of 

 physics were consulted, it was impossible for it to be other- 

 wise, since the permanent existence of such structures was 

 only thinkable if they consisted of a solid substance. Besides 

 this, numerous investigators held the idea that the phenomena of 

 contraction, or changes of form generally, such as protoplasm 

 shows, could only be produced by solid bodies. On the other 

 hand, it was at the same time pointed out that protoplasm 

 behaved very like a fluid. Thus Strassburger, who still upheld 

 the reticular structure of protoplasm, remarked (1882. p. 232) 

 that it was " soft or semi-fluid " ; that it agreed in many of its 

 peculiarities with a colloid, but still more closely, on the other 

 hand, with a fluid, " for it has a tendency to assume the spherical 

 form in a condition of stable equilibrium." Such terms as 

 soft, solid but yielding, jelly-like, semi-fluid, recur continually 

 here and there. Those authors, however, express themselves in 

 the most definite manner who assume, like Pfliiger (1889), that 

 protoplasm is composed of "absolutely solid and absolutely 

 fluid " parts. 



I had, for my part, expressed myself already in 1876 (p. 203) 

 to the effect that " in spite of the objections that are raised 

 against the idea, there are the most cogent arguments for sup- 

 posing that protoplasm obeys the fundamental laws of a fluid 

 mass." My conception of the structure also gave me no reason 

 for departing from this view. In 1886 Berth old in his valuable 

 book again took up the doctrine of the fluid nature of proto- 

 plasm, which had fallen very much into discredit. He did not, 

 however, try to really support it by direct proof, but laid it down 

 as a hypothesis upon which to base his observations and specu- 

 lations upon the structure and upon the phenomena of the move- 

 ment of protoplasm, in order to show the probability of the 

 hypothesis by the ease with which the problem could be worked 

 out. 



What position Schwarz (1887) really takes up with respect 

 to the question of the aggregate condition of protoplasm, is not 

 quite clear to me from his Avork, as I have already pointed out 

 above. As is well known, he denies the reticular framework, 

 and speaks of a "semi-fluid aggregate condition" of the cytoplastin 

 (p. 131). On the other hand, he says on p. 136: "In the 

 cytoplasma no preformed networks and frameworks are present, 

 but a part of it may modify itself into filaments and strands. In 

 consequence of this I must assume that the cytoplasma is a 

 mixture in which, under certain circumstances, a separation can 

 take place of more rigid, viscous, and more fluid dissolved 



