WALLACE 0. FENN 447 



both moving under centrifugal force alone. Centrifugal force is not, 

 therefore, an appreciable factor except in the case of those cells which 

 become "plastered" against the wall of the tube and there ingest 

 particles. This could have been avoided by rearranging the tubes on 

 the drum at intervals. 



This experiment was done under ideal conditions, however, in that 

 there was no air bubble present in the tube. When such a bubble 

 is included in a tube which is slightly inclined to the horizontal, it 

 travels up and down in the tube and stirs the mixture. Under such 

 conditions the rate of phagocytosis, K, should vary in direct proportion 

 to the speed of rotation. This also is true. Thus K was increased 

 from 0.17 to 0.76 (4.5 times) by an increase from 7 to 27 revolutions 

 per minute (3.9 times). 



These two experiments offered a very satisfactory proof of the 

 theory at the outset and the following predictions may be made with 

 considerable assurance. 



1. The rate of phagocytosis, K, may be calculated from the equa- 

 tion for a monomolecular reaction and will remain constant in any 

 experiment as long as the concentration of cells remains constant. 



2. For a given leucocyte suspension in a given medium, K is deter- 

 mined by the chances of colhsion between cells and particles. 



3. The chances of colhsion vary with the method of stirring {i.e. 

 speed of rotation, etc.) but the relative chances of colhsion, R, are 

 applicable however the cells and particles are kept in suspension. 



4. The relative chance of colhsion of any particle is given by the 

 formula i? = (C + Py (Vp - Vc). 



K 7? 



5. The equation — = — should be true for any two sizes of parti- 

 cles, 1 and 2. 



Velocity of Particles. 



The relative chances of collision are, therefore, very simply calcu- 

 lated if the diameter and velocity of the particles and cells are known. 

 The simplest way of determining the velocity of the particles is by 

 direct observation of the speed with which the suspensions settle 

 out in the centrifuge bottle. This can only be done accurately in a 

 suspension of particles of such a uniform size that they all settle at 



