250 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



RESULTS 



I. The optical properties of extracted arthropodin. — A moderately 

 concentrated aqueous solution of arthropodin was examined at fairly 

 low rates of shear.^ A distinct but low flow birefringence was de- 

 tectable, and could be verified as being true birefringence by cancel- 

 lation on slight rotation of the analyzer. The amount of birefringence 

 was much less than that of a myosin solution ^ of roughly similar 

 viscosity. Of more significance, the sign of birefringence was the 

 same as that of the myosin solution (i.e., positive) and the angle of 

 isocline was large but not as sharply defined. These data, crude as 

 they are, show the presence of relatively large anisodiametric par- 

 ticles exhibiting form birefringence. The indefiniteness of the angle 

 of isocline implies a somewhat heterogeneous mixture of particle 

 sizes. Obviously, the optic axes of the particles are the long axes. 



From the above data one would expect the solutions to give a strong 

 Tyndall effect. Examination normal to a beam of light in a dark room 

 shows considerable scattered light which is highly polarized. As per- 

 formed, this only confirms the presence of sizable particles in the 

 solution. 



Thin dried sheets of extracted arthropodin are completely isotropic 

 in surface view. But if the layer dried onto a slide is rather thick it 

 will develop ridges during drying. Occasionally an air bubble will be 

 trapped in such thick films. Both the ridges and the air bubbles set 

 up strains during the final stages of drying such that orientation and 

 hence birefringence is evident along or around each (pi. i, fig. i). If 

 a drop of solution is allowed to dry on a microscope slide under con- 

 tinuous observation, a stage is reached just before complete dryness 

 when fibers can be drawn manually from the viscous mass simply by 

 stirring it with a needle and then withdrawing the needle. Such fibers 

 are of various diameters; most of those drawn were in the range of 

 5 to 50 ju,. Between crossed Nicols these fibers exhibit birefringence 

 which is of positive sign relative to the long axis of the fibers (pi. i, 

 figs. 2-4). That this is indeed birefringence, and not an artifact due 

 to surface reflection or diffraction, can be shown by rotation of the 

 mica plate compensator which produces extinction or intensification. 



Immersion of air-dried sheets or fibers of arthropodin in media of 



2 In the absence of information on molar concentration, viscosity, etc., one can 

 only make general qualitative statements from flow birefringence. The solution 

 used contained the extracted arthropodin from about 100 cuticles in 2 ml. of 

 water. 



3 Chicken leg muscle extract made with 0.5 M KCl at pH 6.5. 



