PROTOPLASM OF PROTOZOA- 97 



are doubly refractive, but the basal granules are not (Engelmann, 

 1880.) Myonemes have been quite generally shown to be anisotropic, 

 especially those in the stalk muscle of the vorticellids (Engelmann, 1875; 

 Wrzesniowski, 1877; Mackinnon and Vies, 1908). The myoneme of 

 the stalk spreads out into fibrillae in the base of the animal. These, too, 

 are doubly refractive. Engelmann (1875) found that the extensile neck 

 of Trachelocerca [Lacrymaria) olor, when stretched out, was positively 

 anisotropic in relation to its longitudinal axis. It is to be recalled that 

 the neck may be extended as much as fifteen times the length of the 

 body. Associated with this is a single spiral thread which becomes 

 straight upon extension of the neck (Penard, 1922). 



Brandt ( 1885 ) has shown that the isospore nuclei of the Radiolaria are 

 anisotropic, but not the vegetative nor the anisospore nuclei. This has 

 been confirmed by Schmidt (1932) on living and preserved material 

 of the same form. Schmidt (1929) had also observed double refraction 

 of the nuclear membrane in living nuclei of a foraminiferan and of 

 Amoeba; in the latter he also observed weak anisotropy of small visible 

 granules (chromatin?) in the living nucleus. Finally, Kalmus (1931) 

 has recorded that certain elements of the division figure of the nuclei 

 of Paramecium show slight traces of double refraction during fission and 

 conjugation. 



X-RAY DIFFRACTION AND ULTRACENTRIFUGATION 



Early studies on cohesion and swelling relations of organic fibrillar 

 structures indicated that the finer structures of which they are composed 

 are micellar in nature. Recently X-ray diffraction methods have sub- 

 stantiated this view and have made it possible actually to measure the 

 dimensions of these structural units. Much of this work has been done 

 on keratin, elastin, chitin, myosin, cellulose, and other nonliving sub- 

 stances. Some observations have been made on living nerve fibers 

 (Schmitt, Bear, and Clark, 1935). 



The evidence from X-ray diffraction shows that animal fibers owe 

 their anisotropic properties to the fact that they are composed of 

 longitudinally oriented protein chains. However, in most protoplasm the 

 configuration of such chains must be such that it may be altered rapidly 

 and reversibly. For a review of X-ray diffraction, see Frey-Wyssling, 

 1938. 



