WALLACE O. FENN 445 



of 1.67 cm. per hour, since the number of particles which got in front 

 of the cell by their brownian motion would be just balanced by the 

 number which would get out of the way of the cell. 



Verification of the Theory by Varying the Speed of Rotation. 



According to the theory, then, the chances of collision determine 

 K, other things being equal. The fact that the chance of coUision 

 is proportional to Vp — Vc, i.e. the difference between the speeds of 

 settling of particles and cells, makes possible a verification of the 

 theory by varying the speed of rotation of the tubes in which the 

 phagocytic mixtures are incubated. 



Returning to Fig. 2, it is evident that the orbits described by the 



V 



particles, being equal to — , must decrease with an increase in n, the 



n 



number of revolutions per unit of time. It should be possible by 



increasing n to decrease the diameter of the orbits nearly to zero. 



Under such conditions there should be less phagocytosis than when 



the mixture is rotated more slowly. In a slowly rotated mixture the 



particles have plenty of time to settle down to the neighboring cells. 



To test this prediction under ideal conditions, six small tubes, 3 mm. 



inside diameter and 1.5 cm. long, sealed at one end, were prepared. 



At the beginning of the experiment all these tubes were filled with 



the mixture of cells and quartz particles immediately after the cells 



were added. The open ends of the tubes were then sealed by dipping 



in melted paraffin, excluding all air. 



Three of the tubes were then put on a drum rotating at 0.3 revolu- 

 tion per minute and three on one rotating at 19 revolutions per minute. 

 Counts were then made of the number of particles present in the 

 remainder of the original mixture. At intervals of about 1 hour one 

 tube was taken from each drum and the number of particles not yet 

 ingested was counted. From these data the phagocytosis constant, 

 K, was calculated by the equation for a monomolecular reaction. 



As predicted, the particles are ingested nearly two and one-half 

 times as rapidly in the slowly revolving tube. Likewise, the cells 

 aggregate more rapidly in the slow tube, due to the greater number of 

 collisions between them. 



