WALLACE O. FENN 477 



Ledingham himself describes "lytic changes" in these leucocytes 

 which he ascribes to the "leuco toxic action of unneutralised bacterial 

 extract." This supposition might also explain the fact observed by 

 Madsen and Watabiki that the rate of phagocytosis decreases more 

 rapidly than the concentration of bacteria, the cumulative effect of 

 the toxic substance finally preventing phagocytosis altogether before 

 all the bacteria are ingested. 



Other Experiments on Phagocytosis of Carbon. 

 The Effect of Serum. 



Hamburger (5) found that the carbon particles which he used with 

 horse leucocytes were ingested just as well in pure sodium chloride 

 as in sodium chloride and serum. Fig. 5 shows that this was dis- 

 tinctly not the case in these experiments. In this figure Hamburger's 

 measure of phagocytosis was used; i.e. the percentage of cells con- 

 taining carbon. These values are plotted as ordinates in Fig. 5 

 against time as abscissse. Two controls, one without serum and 

 one with serum, heated to 56°C. for 40 minutes, showed almost no 

 phagocytosis. This is the usual result obtained by previous workers 

 on phagocytosis of solid particles, although there is considerable 

 disagreement. Hamburger finds senmi necessary for the phago- 

 cytosis of starch but not of carbon. 



Forges (6) found that starch is taken up from isotonic solutions 

 without serum as well as with serum, but the accelerating effect of 

 serum became evident in hypertonic solutions. 



Ouweleen (7) concludes that two substances are necessary for the 

 phagocytosis of starch: (1) a thermolabile constituent of serum which 

 is absorbed on the starch and causes adhesion of the starch to the 

 leucocyte; and (2) a substance causing the adhering particle to be 



not a linear function of the opsonin concentration. From his figures for the 

 number of bacteria ingested in the presence of known concentrations of opsonin, 

 it is possible to calculate graphically what the true concentration of opsonin must 

 be after adsorption to account for the observed number of bacteria ingested. 

 Using figures so obtained the adsorption formula no longer applies. In only one 

 experiment, however, were his data sufficiently complete to make this method of 

 analysis possible. 



