452 PHAGOCYTOSIS OF SOLID PARTICLES. I 



from the same original stock bottle, the large particles being removed 

 by centrifugalization each time. It is not surprising, therefore, that 

 the measurements should differ somewhat at different times even by 

 the same method. 



Diameter and Velocity of Leucocytes. 



The leucocytes were obtained from rats. The animals were injected 

 intraperitoneally with a suspension of aleuronat, and the peritoneal 

 cavity was opened on the followdng day and washed out with 0.5 

 per cent sodium citrate in 0.9 per cent sodium chloride solution. The 

 cells were then centrifuged once to get rid of the citrate and resus- 

 pended in salt solution. If the cells are not washed thus it is neces- 

 sary to have so much citrate present to prevent clotting of the exudate 

 that it prevents phagocytosis. 



For these experiments it was of first importance to determine the 

 diameter and velocity of the leucocytes. These determinations had 

 to be done independently as the density could not be measured 

 directly. The diameter was measured directly in the microscope on 

 fresh specimens before they had had time to spread on the microscope 

 slide. The velocity was determined by the stop-cock method. An 

 average of five determinations was 1.67 ± 0.05 cm. per hour. The 

 figures were as follows: 1.63, 1.56, 1.83, 1.47, 1.84. 



Since, however, the leucocytes are not of the same size it is neces- 

 sary, in order to calculate the chances of collision with any accuracy, 

 to divide the cells into three groups of three average diameters and 

 calculate the chances of collision for each group separately. These 

 calculations were made as follows: The diameters, D, of the leucocytes 

 were measured as already described. From these data a frequency 

 curve was obtained which was divided into three parts (Table II). 

 The relative velocities of the three groups were then calculated by 

 the formula V = D^K, where X is a constant. From these velocities 

 the average velocity may be calculated as shown by multiplying the 

 velocity for each group by the percentage of total cells in that group 

 and dividing the sum of the results by 100. But the average velocity 

 was found by experiment by the stop-cock method to be 1.67 ± 0.05. 



Equating these we have 



1.67 ±0.05 = 81.0 ii: 

 K = 0.0206 ± 0.00062 



