340 



Capt. S. R. Douglas. On the Role of the 



reduced to 1 in 6000, a strength which has little or no inhibitory effect on 

 phagocytosis. 



Two small test-tubes were now filled in with the following mixtures : — 



Tube I. 250 c.mm. of washed corpuscles. 

 250 c.mm. of unheated serum. 

 100 c.mm. of the emulsion of plague bacilli. 



Tube II. 250 c.mm. of washed corpuscles. 



250 c.mm. of serum heated to 60° C. for 20 minutes. 

 100 c.mm. of the emulsion of plague bacilli. 



Both tubes were incubated in a water bath at 37° 0. and after stated 

 intervals samples from each were removed with a capillary pipette. From 

 these, films were made which were fixed with a saturated solution of mercuric 

 chloride and stained with carbol thionin. 



The number of bacilli contained in 100 leucocytes was now estimated. 



This was by no means an easy task in the case of some of the films made 

 from the samples taken from tube I, in which owing to the presence of the 

 unheated serum the bacilli were undergoing intraleucocytic digestion. 



The numbers given below include not only the organisms which, because 

 of their perfect shape and staining, were deemed unaffected by the leucocytic 

 digestive fluids, but also many which showed signs of commencing digestion. 



Time 

 of incubation. 



Number of bacilli in 

 100 leucocytes in samples 

 from Tube I, containing 

 unheated serum. 



Number of bacilli in 

 100 leucocytes in samples 

 from Tube IT, containing 

 heated serum. 



15 minutes 



330 



80 



30 „ 



280 



140 





210 



210 



2 hours 



95 



280 



3 „ 



57 



250 



4 „ 



27 



300 



On examining the figures thus obtained, assuming that no more bacilli were 

 ingested by the leucocytes after the first 15 minutes' incubation, the only 

 conclusion that can be drawn is that 90 per cent, of those organisms which 

 were ingested in the first 15 minutes have been so completely digested during 

 the succeeding 3| hours that they no longer can be recognised as bacteria. 



But most probably what does happen is that the leucocytes continue to 

 take up microbes to some extent during the whole period of incubation, so 

 that in reality even a greater percentage than 90 per cent, of those microbes 

 which were ingested by the leucocytes in the first 15 minutes have been 



