580 PHAGOCYTOSIS OF SOLID PARTICLES, in 



from these figures that there is great variation in different experiments 

 in the relative rates of ingestion of carbon and quartz, the ratio vary- 

 ing from 0.7 to 11.5. That this ratio may vary with the condition 

 of the cells, even in the same experiment, will be shown later by 

 another method. 



Another contributing explanation is perhaps the agglutination of 

 the carbon. In some experiments the carbon has been observed to 

 be more stable than in others. This factor could always be controlled, 

 however, by observation of the samples which were removed from 

 the incubation mixtures at intervals for counting. Whenever any 

 considerable agglutination was observed the experiment was dis- 

 carded. With quartz, however, there was seldom any agglutination, 

 and this is the most characteristic difference between the behavior 

 of the two kinds of particles. Thus quartz can be thrown down 

 repeatedly by centrifugalization, and when resuspended in water 

 the particles are perfectly discrete. This cannot be done with carbon 

 unless it is stabilized with acacia. This suggests that the cause of 

 the more rapid agglutination may also be the cause of the greater 

 speed of phagocytosis. One might suppose that if carbon agglutinates 

 with carbon readily, it will also agglutinate readily with cells, where- 

 upon ingestion promptly occurs. 



Comparison of Quartz and Carbon by the ''Film" Method. 



Before proceeding to a discussion of this hypothesis, however, 

 some experiments will be reported in which the rates of ingestion of 

 carbon and quartz were compared by another method, which will be 

 referred to as the "film" method. By this method, unlike the "sus- 

 pension" method described previously, phagocytosis was allowed to 

 proceed in a thin film between the slide and cover slip. Both cells 

 and particles immediately settled out. The leucocytes crept about 

 on the slide and ingested the particles. 



A cover-slip was supported at its center and four corners by frag- 

 ments of another fairly thick cover-slip. While held down with a 

 small weight it was sealed at the corners with collodion. The weight 

 prevented the cover-slip from floating up on the collodion, and made 

 the distance from slide to cover uniform throughout. A thick sus- 

 pension of cells with equal numbers of carbon and quartz particles 



