192 L. V. HEILBRUNN. 



coagulation within the egg. The distinguishing feature of a gel 

 as opposed to a sol is its greater viscosity. All other macroscopic 

 differences depend upon this. Indeed, according to Freund- 

 lich, the viscosity of a colloidal solution may be taken as a measure 

 of its tendency to gelatinize ("Gelatinierungsbestreben"). 1 

 The viscosity of the Arbacia egg protoplasm was regarded as an 

 index of the state of aggregation of its constituents. 



There are two general methods of measuring viscosity. One 

 can either measure the rate of flow of a fluid, or one can study 

 the movement of particles through the fluid. Both of these 

 methods were used in studying the viscosity of the Arbacia 

 cytoplasm. It is very easy to observe the rate of flow of the 

 egg cytoplasm. One has only to exert pressure on the coverslip 

 and the vitelline membrane soon bursts, allowing the egg con- 

 tents to flow out. With this method, only great changes in 

 viscosity can be noted, but gelatinization always does produce 

 a very great increase in viscosity, so that the method usually 

 suffices. The pressure can be applied by pushing on the cover- 

 slip with the point of a dissecting needle, or if greater accuracy 

 is desired, a square piece of glass (broken from a slide) can be 

 dropped from a known distance. This method of observing 

 changes in viscosity is not entirely above criticism; for cortical 

 changes, produced by the reagents used, might have an effect 

 on the size of the aperture through which the cytoplasm flows. 



The second method is much more exact and reliable. It 

 involves a study of the movement of granules through the 

 cytoplasm. The force which must be exerted to push the 

 granules through the cytoplasm is a measu e of the viscosity of 

 the latter. Centrifugal force is of necessity used, and a hand 

 centrifuge does very nicely. 2 Into one tube of the centrifuge 

 are placed eggs which have been treated in various ways; into 

 the other, normal eggs. After the centrifuging has been accom- 

 plished, a microscopic examination reveals any differences which 



1 Freundlich, '09, p. 416. Freundlich and Ishizaka, '13. 



2 A Bausch and Lomb instrument was used in my experiments, and the eggs 

 were placed into the small glass tubes of the haematocrit attachment. New tubes 

 were used in each experiment so that all danger of contamination was avoided. 

 One turn of the high-speed handle involved 130 revolutions of the tubes. The 

 distance between the end of each tube and the axis was approximately 7^ cm. 



