466 PHAGOCYTOSIS OF SOLID PARTICLES. II 



the hemoglobin and serum proteins act fairly efficiently as protective 

 colloids, and the normal reaction of blood, at which these experiments 

 were done, is slightly alkaline. Otherwise, it would be impossible to 

 keep the particles distinct in 0.9 per cent sodium chloride with the 

 leucocytes. Even so, the agglutination of the carbon was a very 

 serious complicating factor in these experiments, more so than with 

 quartz. 



In view of the readiness with which these uniform suspensions 

 agglutinate, it is a significant fact that in the stock suspensions, from 

 which the large particles have not yet been removed, all the par- 

 ticles are never agglutinated even after being kept for nearly a year 

 without acacia. It would seem as if coagulation must reach an 

 equilibrium and stop. It is certain that there is always an abun- 

 dance of the smallest sized particles which are not clumped and can 

 readily be separated from the larger particles and the clumps by 

 settling. 



Chances of Collision with Leucocytes. 



The diameters of the particles in the two suspensions and the diam- 

 eters of the leucocytes were measured microscopically. The varia- 

 tion in these diameters is shown in three frequency curves in Fig. h 

 On account of the lack of uniformity of these suspensions the chances 

 of collision between leucocytes and particles could not be calculated 

 from the average diameter and velocity of all the particles in the 

 suspension. It was, therefore, necessary to divide each frequency 

 curve, as given in Fig. 1, into sections and calculate the chances of 

 collision, i?, for each possible combination, by the form.ula R = 

 (C + Py {Vp — Vc) (1). Here the first term is the square of the 

 sum of the diameters of the cell and particle, and allows merely for 

 the larger target offered by a large particle. The second term is the 

 difference in velocity between the cells and particles. Since the 

 velocities of the cells and particles in this case were nearly equal, a 

 small error in Vp or Vc would make a large error in R. It was, there- 

 fore, necessary to divide the carbon suspensions into six groups each 

 to obtain sufficient accuracy in the calculation. The leucocytes were 

 divided into three groups as described in the previous paper. The 

 total chances of collision were then given by the sum of the 18 (6 X 3) 



