WALLACE O. FENN 



467 



group chances of collision, each multiplied by the percentage of cells 

 and of particles in that particular group. The data from which the 

 chances of collision were taken are given in Table I together with the 

 chances of collision of each suspension. 



It will be noted that in calculating the chances of collision the 

 velocity was determined experimentally and was not calculated from 

 the diameter and density. This was done because of the fact that 

 the velocity of carbon particles is not proportional to the density of 

 dry carbon which is full of capillary spaces, but to its density with 



Number of 

 ParTicles 

 or Cells 



Leucocytes 



10 12 



Diamerers in Microns 



Fig. 1. Frequency curves showing the variation in the diameters of two car- 

 bon suspensions and the leucocytes. Curves are plotted on such a scale that 

 the subtended areas are approximately equal. Ordinates represent number of 

 particles for a given interval of the abscissEe, which represent the diameters in 

 microns. Points plotted are experimental points. In the case of the carbon sus- 

 pensions they are smoothed by averaging each point with the two adjacent points. 



these spaces full of water; and the latter is not easily determined. 

 However, having obtained the velocity of each group directly, with- 

 out using any value for the density, it is possible to reverse the proc- 

 ess and calculate both the density and the volume of the capillary 

 spaces, as a check on the accuracy of the measurements. 



By a simplification of Stokes's law for the velocity, V, of a particle 

 of diameter, P, and density, D, in a medium of density 1.00 and 

 viscosity 0.010 under the acceleration of gravity, we obtain the 

 equation 



