476 PHAGOCYTOSIS OF SOLID PARTICLES. II 



the phagocytosis of solid particles. This can only be determined if 

 the number of bacteria ingested in proportion to the number of 

 bacteria present is known. In most experiments on phagocytosis of 

 bacteria no counts have been made of the total number of bacteria 

 present. The only data known to the writer from which this point 

 can be determined are those of Madsen and Watabiki (3) and of 

 Ledingham (4). The former measured the number of bacteria 

 ingested as a function of time. Their curves follow the law of a 

 monomolecular reaction fairly well if all the bacteria not ingested at 

 the close of the experiment, i.e. when phagocytosis has ceased, are 

 disregarded. The rate of phagocytosis is, therefore, not proportional 

 to the concentration of the bacteria present. 



Ledingham did for phagocytosis of bacteria what was done in 

 Figs. 3 and 4 for the phagocytosis of carbon. He measured the 

 number of bacteria ingested in unit time by a given number of cells 

 from a series of bacterial suspensions of varying known concentra- 

 tions. If the reaction had been of the monomolecular type the per- 

 centages ingested at each concentration should have been equal, just 

 as all the K\ in Figs. 3 and 4 were equal for the same size particle. 

 He found, however, that as the concentration of bacteria decreased, 

 the percentage ingested first increased and then decreased. There is, 

 therefore, no evidence that the phagocytosis of bacteria follows the 

 law for a monomolecular reaction. If, as Ledingham believes, the 

 comparatively slight decrease in the percentage ingested in low con- 

 centrations of bacteria is due to experimental error, the decrease in 

 higher concentrations may be due to increasing concentrations of 

 some substance given off by the bacteria which is toxic to the cells. ^ 



^ In these experiments Ledingham's object was to prove that phagocytosis of 

 bacteria obeys FreundUch's exponential formula for adsorption, but it is hard 

 to see how the formula could have any significance for phagocytosis even if appli- 

 cable. He also tries to show that the adsorption of opsonin from serum by bacteria 

 follows the same law, but his measure of the concentration of opsonin adsorbed 

 is mathematically incorrect. He assumes that the opsonin adsorbed by the 

 bacteria is proportional to the difference in the number of bacteria ingested by a 

 given number of leucocytes in the presence of an opsonin solution, before and after 

 that solution has been treated with a given bacterial emulsion (which adsorbs 

 some of the opsonin) and freed from it by centrifugalization. His own figures 

 show, however, as he himself observes, that the number of bacteria ingested is 



