WALLACE O. FENN 469 



1.81 being the density of dry carbon. Whence, introducing the 

 calculated values for D and solving, we get x = 0.49 ± 0.09 and 0.34 

 db 0.07, the average being 0.42 cc. of capillary space per gram of 

 carbon. Though the variation is relatively large it is indicative of 

 the general accuracy of the calculations that this is the exact figure 

 given for the volume of the capillary spaces in charcoal by Cude and 

 Hulett (2), from a study of a large series of charcoals used by the 

 Chemical Warfare Service. 



It is possible, then, to predict the behavior of the leucocytes toward 

 the particles of these suspensions when they are incubated together. 

 The predictions are: (1) that the large particles will be taken up more 

 rapidly than the small particles, the initial ratio of the rates of inges- 

 tion being as 248 : 144 = 1 : 0.58; and (2) that this ratio will 

 probably increase with time. The latter prediction is illustrated by 

 the following figures for the ratio of the chances of collison of the 

 two suspensions at such times during the reaction that 25, 50, and 

 75 per cent of the larger particles are ingested. 



Change in Ratio Predicted during Reaction. 



This change in ratio is largely due to lack of uniformity of the 4.7^ 

 suspension, the largest particles having an abnormally high chance 

 of collision as shown in Table I. The prediction is, however, merely 

 a probability since the assumption upon which it is based, namely 

 that the leucocytes remain unchanged in concentration, can never be 

 completely true. However, it may be noted that the experiments 

 largely verify these predictions. 



Method of Measuring Phagocytosis. 



The detailed technique of these experiments is given in a previous 

 paper (l). It is sufficient to state here that mixtures consisting of 

 washed leucocytes from rats, carbon suspension, and serum were 



