WALLACE O. FENN 



577 



sufl6.ce here to state that R is proportional to the difference between 

 the velocities of leucocytes and particles, Vp — Vc, and to the square 

 of the sum of the diameters of cells and particles, (C + P)^. The 

 latter factor allows for the fact that a larger particle makes a larger 

 target. The rate of phagocytosis is measured by iT of a monomolec- 

 ular reaction and is equal to the slope of the straight Kne obtained 

 by plotting against time the logarithms of the number of particles not 

 yet ingested, as determined by frequent counts on an ordinary hemo- 

 cytometer. The cell suspensions were obtained from peritoneal 

 exudates in rats. The phagocytic mixtures were rotated slowly on a 

 revolving drum during incubation to prevent settling out of the cells 

 or particles. 



TABLE I. 



Calculated Chances of Collision, R. 



The results of one such experiment are plotted in Fig. 1. Since 

 ordinates represent the logarithms of the number of particles counted 

 at time, t (abscissae), outside the leucocytes, the steeper the slope of 

 the curve the more rapid the phagocytosis. A straight Kne in this 

 figure, i.e., a constant K, indicates that the same percentage of the 

 number of collisions occurring between cells and particles is resulting 

 in ingestion throughout the experiment. As has previously been 

 pointed out, it is only the initial slope, in cases where K is not constant, 

 which is expected to agree with the theoretical predictions. In Fig. 1, 

 the initial K's of the two carbon experiments are 0.33 and 0.41, and 

 of the quartz, 0.38 and 0.32 the averages being 0.37 and 0.35 respec- 

 tively; i.e., carbon is taken up ^5 or 1.06 times as fast as the quartz. 

 Reference to Table I, however, in which are tabulated the chances 

 of colHsion of the three quartz and two carbon suspensions used in 



