338 



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



red blood cells, or, as the case may be, the bacteria, in such a manner that 

 they undergo digestion when brought into contact with solutions of trypsin 

 or leucoprotease, solutions which have been found to be quite inert on 

 suspensions of red blood cells or bacteria which had been previously acted on 

 by heated serum or simply suspended in normal saline solution. 



It is proposed to call this property of the serum the " protryptic " 

 property of the serum, indicating that the serum by this action prepares the 

 organisms or red blood cells for digestion by the leucocytic digestive fluids. 



Experiments made to Ascertain whether only those Bacteria which had been 

 Phagocytosed in the Presence of Unheated Serum were Liable to Undergo 

 Intra-leucocytic Digestion. 



Having found that plague bacilli are taken up by the leucocytes in 

 considerable numbers, even in the presence of heated serum, an emulsion in 

 normal saline solution of B. pestis was made from a 24-kour-old agar culture. 



Human blood corpuscles (S. K. D.'s) were washed free from serum by 

 centrifuging them in several changes of salt solution, and two samples of 

 serum (S. K. D.'s) were obtained, one of which was heated to 60° C. for 

 10 minutes. 



Two capillary tubes, such as are used in ordinary opsonic estimations, 

 were now filled in with the following mixtures : — 



Tube I contained : — 



2 volumes of the washed corpuscles. 

 2 volumes of the unheated serum. 



1 volume of the emulsion of B. pestis. 



Tube II contained : — 



2 volumes of the washed corpuscles. 



2 volumes of the serum heated to 60° C. for 10 minutes. 

 1 volume of the emulsion of B. pestis. 



These tubes were then incubated at 37° C. for four hours, after which 

 films were made of samples of their contents, fixed in a saturated solution of 

 corrosive, sublimate and stained with carbol-thionin. 



On examination, the microscopical preparations made from both tubes 

 showed abundant phagocytosed bacilli, but whereas in the case of those 

 made from Tube II, in which heated serum had been used, the bacilli lying 

 in the leucocytes were deeply stained and perfectly sharp cut in appearance, 

 in those made from Tube I, in which unheated serum had been used, the 

 bacilli taken up by the leucocytes were almost completely digested, appearing 

 as swollen, ill-staining shadows, frequently lying in well marked vacuoles. 



