470 PHAGOCYTOSIS OF SOLID PARTICLES. II 



incubated at 37°C. in small test-tubes (8 mm. inside diameter), 

 placed horizontally on a drum revolving uniformly about its horizon- 

 tal axis. The speed of rotation was usually about 15 revolutions per 

 minute. In these experiments no precautions were taken to prevent 

 an air bubble from traveling up and down in the tube as it revolved. 

 Samples were removed at intervals and counts were made of the 

 number of particles not ingested by the leucocytes. 



The measure of phagocytosis desired is, then, the per cent of the 

 collisions occurring between cells and leucocytes which result in 

 ingestion. But the number of leucocytes being the same in any one 

 experiment, the relative number of collisions is proportional only to 

 the number of particles. If the percentage of collisions resulting in 

 ingestion is constant and the concentration of cells does not change, 

 the rate of ingestion will always be proportional to the number of 

 particles still free to collide, and the velocity constant, K, will be 



1 A 



given by the equation for a monomolecular reaction, K = ~ log 



/ A — X 



where A is the original number of particles and x is the number 

 ingested in time, t. Here the relative value of K is dependent only on 

 the percentage of coUisions resulting in ingestion, and is, therefore, 

 the measure of phagocytosis desired. K has been determined in 

 practice by plotting the logarithms of the number of particles still 

 free, i.e. log A — x, against time and determining the slope graphi- 

 cally. The points should lie on a straight line if K is constant. 

 This is more accurate than calculating K directly from the formula, 

 since the formula attaches special importance to A which is known 

 no more accurately than the rest of the points. 



Where K is not constant the initial value of K only is determined. 

 A decrease in K with time may be due to : 



1. Decrease in the number of cells by agglutination. ^ 



2. Decrease in the capacity of cells for particles. 



3. Lack of uniformity in the suspensions resulting in decrease in 

 chances of collision as larger particles in each suspension are ingested 

 more rapidly than the small particles. 



^ It can be shown that in calculating the chances of collision the decrease in the 

 number of cells by agglutination is not compensated for by the increase in velocity 

 and size of the resulting clumps. 



