PROTOPLASM OF PROTOZOA 87 



cells a material called plasmosin, which he thinks is constituted of linear 

 micelles. 



The formation of a fiber results from the end-to-end orientation of these 

 linear micelles. In protoplasm in the liquid state these micelles are probably 

 independent and irregularly arranged but in flowing protoplasm they would 

 be oriented parallel to the axis of flow. . . . From this state by simple 

 end-to-end combination all changes in viscosity are possible up to the forma- 

 tion of a fibrous gel . . . or even discrete fibers. 



Bresslau (1928) has also shown that "tektin," a material extruded by 

 ciliates, has anisotropic properties somewhat similar to those of plasmo- 

 sin. 



The fact that the chromosomes probably represent gene-strings has 

 been of enormous importance in determining our ideas of significant pro- 

 toplasmic structure. The chromosomes apparently reproduce themselves 

 at each cell division, so that their individuality is retained in all cell 

 generations. The demonstration of the presence of these linear aggregates 

 of visible size, which are self-perpetuating, cleared the way for the micel- 

 lar theory of protoplasm structure. 



Much of the evidence for the presence of linear aggregates in proto- 

 plasm has been obtained by microdissection, by the use of dark-field and 

 polarization microscopes, by studies on cohesion and swelling, and by 

 X-ray dififraction methods. Some of these have already been considered 

 and others will be discussed below. 



ELASTICITY 



According to Seifriz (1936), "elasticity is the best indication we have 

 of the structure of living matter" and is evidence for the presence of 

 linear aggregates. A body is said to be elastic if after having been strained 

 it tends to return to its original form when the stress is removed. Volume 

 elasticity is characteristic of fluids and solids; shape elasticity (rigidity) 

 of solids and colloids in the gel condition generally. The form assumed 

 by the bodies of various flagellates and ciliates is characteristic and 

 offers means of identification in many instances. Relative rigidity is of 

 common occurrence among those Protozoa, such as Euplotes, which have 

 a dififerentiated pellicle and a firm ectoplasm. C. V. Taylor (1920) 

 demonstrated this elasticity by applying pressure with a microneedle; the 

 body bent conspicuously over the needle but returned to normal shape 



