36 STUDIES IN IMMUNITY. 



its normal reaction for the basic stain. Mononuclear leucocytes also 

 have a very distinct affinity for diphtheria bacilli and take up a good 

 number of them, but the organisms taken up by the mononuclears 

 show fewer color changes than those taken up by the polynuclears. 



Bacillus proteus vulgaris. The change to a red staining bacillus 

 is still more striking with Proteus vulgaris than with the diphtheria 

 bacillus. After contact for quarter of an hour with a rich leu- 

 cocytic exudate, eosin-stained bacteria may be found within the 

 phagocytes. It is evident that the protoplasm of leucocytes has a 

 very marked action on Proteus. After a few hours' contact it is 

 very hard to find any organisms in the phagocytes that stain blue. 

 But although these bacteria are very much changed in their chemical 

 constitution, they show little morphological alteration. The bac- 

 teria scattered in the surrounding fluid are normal in appearance, 

 with the exception of a few individuals that stain red. Proteus is 

 one of the best organisms to demonstrate phagocytosis in vitro, 

 and shows most clearly the effect of leucocytic fluid. 



B. anthracis. The engulfing of the anthrax bacillus by phag- 

 ocytes in vitro is easily demonstrable. The polynuclears take up 

 one or two rods; when the chain of bacteria is long, it frequently 

 happens that several phagocytes join together about the chain and 

 unite in absorbing it. The filaments that have been taken up stain 

 red or a shade between red and blue. There are to be noted, it is 

 true, in the surrounding fluid also bacteria in which changes are 

 quite evident, and it must be admitted that the fluid of the exudate 

 seems to show bactericidal effects on this organism. But a careful 

 study of smears shows clearly that these substances in the surround- 

 ing fluid have come by diffusion from the leucocytes. It is per- 

 fectly evident that the red-stained bacteria are more numerous 

 within the phagocytes than without them; and, what is more, it is 

 not unusual to find long threads of anthrax stained blue throughout 

 their length, with the exception of those spots in contact with the 

 protoplasm of a leucocyte. Such a picture shows well the phag- 

 ocytic origin of the soluble substances that are harmful for the 

 anthrax bacillus. 



B. musco'ides. Abundant phagocytosis. Extracellular organ- 

 isms normal. Within the phagocytes reddish or bluish rods. 



B. vermicularis. Same result. 



