1907.] Substance in Serum ivhich influences Phagocytosis. 401 



strength serum. This appears in a table in Wright and Douglas' (1903) paper, 

 but no remark is made on the significance of the phenomenon. 



The normal serum of several species of animal tested behaved in a similar 

 manner in respect to dilution, as appears in Table II. 



Table II. — Effect of Dilution of Normal Serum of Different Species. The 

 Numbers indicate the Average Number of Micro-organisms taken up 

 per Leucocyte. 



Serum ...< 



Human 

 serum and 

 leucocytes. 



Horse's 

 serum and 

 leucocytes. 



Pig's 

 serum and 

 leucocytes. 



Rabbit's 

 serum and 



human 

 leucocytes. 



Human ; 

 serum and 

 leucocytes. ] 



Micro-organism < 



Staphylo- 

 coccus. 



Staphylo- 

 coccus. 



Staphylo- 

 coccus. 



Staphylo- 

 coccus. 



Tubercle 

 bacillus. 



Concentration of serum — 



1 



i 



4 



i 



1 

 "16 



9-7 

 9-6 

 10-0 

 8-2 

 8-5 

 6'4 

 2'3 



23-7 

 28-5 

 14-6 

 13 

 11-9 

 6-8 



12 7 

 15'8 

 14-9 

 12-3 

 5 2 

 6-7 



16-4 



17'0 



12 6 



9*2 



3-0 



2-4 



8 3 

 12-2 



9 5 

 5 3 

 4-8 

 2-5 

 1-6 



In addition to the experiments with staphylococcus, an experiment with 

 the tubercle bacillus was also made, which shows that this relation is not 

 limited to one micro-organism. Five dilution experiments on normal human 

 serum, the diluent being normal salt solution, and the organism being the 

 Staphylococcus pyogenes aureus, have been made. 



The mean figures of these experiments for the pure serum, and the successive 

 dilutions down to 1 in 32, if expressed in terms of unity are, 



1, 1-16, 1-02, 071, 0-53, 0-35, 



and the corresponding concentrations of serum, ' 



1, 0-5, 0-25, 0125, 0-0625, 0-03125. 



I am indebted to Dr. J. C. G. Ledingham for pointing out to me that after 

 the second number there exists an approximate constant ratio between the 

 second series and the squares of the first, as shown below : 



(1-02) 2 = 4-2 (0-25), 



(0-71) 2 = 4-03 (0-125), 



(0-53) 2 = 4-4 (0-0625), 



(0-35) 2 = 3-9 (0-03125), 



and that if the points (0*25, r02),(0125, 0'71), (0'0625, 0'53), (0*03125, 0'35) 



