THE STRUCTURE OF PROTOPLASM 263 



agitation with a dissection needle, less sudden and pronounced 

 than that just cited, are common. These phenomena are all 

 duplicated in colloidal systems. Thixotropic behavior in gels 

 is now a commonly known happening. W. Ramsden gives 

 another case which is comparable. He tells of pouring a dilute 

 filtered solution of white of egg repeatedly to and fro from one 

 test tube into another or vigorously shaking it in a closed vessel, 

 with the result that numerous loose fibrin-like flakes develop 

 in the liquid. They consist of agglutinated protein and are 

 permanently insoluble in the mother liquid. It is even possible 

 by prolonged shaking to convert the whole of the protein into 

 an insoluble solid. Protein molecules are simply aggregated 

 into visible masses of solid, but no coagulation has taken place. 

 The viscosity of gelatin solutions is lowered by agitation alone, 

 which is evidence in favor of a structure such as that postulated 

 here. The same viscosity changes in protoplasm from the same 

 causes rest on the same structural features. 



That the mitotic figure (Fig. 17), including the much con- 

 troverted spindle fibers, owes its existence to structural features 

 resting upon the orientation of linear crystalline units seems 

 very likely, especially in view of Zocher's observations. He 

 saw the parallel orientation of rod-shaped particles in a vanadium 

 pentoxide sol; doubly refractive (crystalline) images resulted 

 which greatly resembled the mitotic spindle of cells (of eggs 

 immediately after fertilization). Belaf, Freundlich, Runn- 

 strom, Spek, and others regard the mitotic figure as the outcome 

 of an orientation of fibers. 



Further support for linear units in protoplasm comes from a 

 number of diverse observations; thus. A, R. Moore finds that 

 Plasmodia when forced through moderately fine sieves do not 

 live; but they may of themselves flow through exceedingly 

 fine sieves. Forcing presumably crushes the long protoplasmic 

 fibers, but in flowing naturally the protoplasm can take its 

 fibers through much finer pores. Moore believes the micro- 

 fibrils to be of the order of 5 X 10~^ mm. in diameter and two 

 thousand times as long. Peters has postulated similar but finer 

 molecular threads in protoplasm. 



It is of further significance for the problem of protoplasmic 

 structure to realize that while polarization studies of protoplasm 

 have not shown living matter generally to be anisotropic, yet 



