DIFFUSION IN DEFORMED GELS 91 



diffusion zone becomes elliptical, as will be gathered from the 

 following figures, which refer to the set previously quoted : 



Prism I. Prism 11. 



Original height 28 mm. : 



Height after release . . . 24-2 25-0 



Major axis of diffusion zone . . 15*0 15-0 



Minor axis of diffusion zone . . 11 '5 i2-i 



If, therefore, diffusion takes place during temporary de- 

 formation the diffusion zone may, after removal of the stress, 

 simulate a marked anisotropy, a point which may possibly 

 be of histological interest. Even fairly small and transitory 

 deformations may leave a permanent record in this fashion. 



Concurrently with the quantitative experiments just de- 

 scribed a number of qualitative ones were carried out, in which 

 a reaction producing Liesegang stratifications was made to 

 proceed in deformed gels. The conditions with this arrange- 

 ment are too complicated for quantitative investigation, as 

 the deformation may conceivably affect other factors besides 



B 



Fig. 2. 



the diffusion velocity. The test pieces in these experiments 

 were short right cylinders : the parallel ends were closed by 

 glass plates, put on warm, so as to confine diffusion to the 

 peripheral surface and eliminate the well-known complications 

 when diffusion into a gel takes place through two faces meeting 

 in a sharp edge. The cylinders were then deformed by a simple 

 device so that the originally rectangular axial section (Fig. 2a) 

 became approximately trapezoidal (Fig. 2b), care being taken 

 to keep the one side — the left in the illustration — as far as 

 possible its original length. The compression in the principal 

 axial section accordingly increases in — probably — linear ratio 

 from left to right. The cylinders thus deformed were completely 

 submerged in the reacting solution, the progress of diffusion 

 being readily observed through the upper glass plate. Towards 

 the end of the experiment gradually increasing quantities of 

 formaldehyde were added to the solution so as to harden 

 the test pieces completely before they were released and cut 

 through. From the hardened gelatin the glass plates detach 

 themselves quite easily. 



The reaction employed was that between tribasic sodium 



