FACTORS DETERMINING PHAGOCYTOSIS 325 



less phagocytosis per cell occurs in the emulsion containing the 

 greater number of leukocytes. This phase of the subject has been 

 taken up most thoroughly by Hektoen 59 and his associates, and Rose- 

 now 60 has made careful comparative studies on pneumococcus 

 phagocytosis, in which he standardized the leukocytic suspensions by 

 actual cell counts. His work as well as that of Tunnicliff, 61 of the 

 same school, has shown definitely that the inherent phagocytic power 

 of leukocytes may vary not only in health and disease, but differences 

 may exist between the cells of apparently normal people. Tunni- 

 cliff showed, for instance, that at birth the leukocytes are less active 

 than in adult life. 



For accurate experimental work, therefore, as well as in theoret- 

 ical reasoning upon problems of phagocytosis, it is necessary to bear 

 in mind the possible inherent variations in the leukocytes themselves. 



Of the three factors concerned in the process of phagocytosis, 

 then, we have considered two, the serum and the leukocytes. The 

 former we have seen exerts a powerful determinative influence on 

 the process, the latter a less marked influence, though still definite 

 and measurable. We have still to discuss the bacteria themselves 

 as variable factors in determining the degree to which phagocytosis 

 may take place. 



This problem was first investigated by Denys and Marchand in 

 connection with their work upon streptococcus immunity, and was 

 further studied in detail by Marchand. Marchand 62 showed that 

 leukocytes would readily take up non-virulent streptococci in the 

 presence of normal serum, but that under similar conditions virulent 

 streptococci were not phagocyted at all or to a very slight degree 

 only. He determined further that this resistance to phagocytosis 

 remained unchanged after the virulent organisms had been killed 

 by heat, and washed clean of culture fluid. It seemed, therefore, 

 that the resistance depended upon a condition of the bacterial body 

 and not upon substances secreted and given off to the environment. 

 These experiments, as well as similar work by Mennes, 63 Gruber and 

 Futaki, 64 and others makes it clear that differences in virulence 

 between different species of bacteria, as well as between different 

 strains of the same micro-organism, depend, at least in part, upon 

 the resistance which the bacterial bodies oppose to ingestion by the 

 leukocytes. We must distinguish clearly here between these appar- 

 ently purely "antiopsonic" bacterial properties and those supposedly 

 "antichemotactic" substances which are conceived as a cause for 



59 Hektoen. Jour, of A. M. A., Vol. 57, No. 20, 1911. 

 60 Rosenow. Jour, of Inf. Dis., 7, 1910. 



61 Tunnicliff. Jour. Inf. Dis., 8, 1911. 



62 Marchand. Arch, de Med. Exp., No. 2, 1898. 



63 Mennes. Zeitschr. f. Hyg., Vol. 25, 1897. 



64 Gruber and Futaki. Munch, med. Woch., 1906. 



