570 INFECTION AND IMMUNITY. 



microns), is non-motile and shows polar staining. 

 It resembles the plague bacillus in form, but is 

 somewhat smaller, and does not show the exten- 

 sive involution forms of the latter. In the ulcer 

 it lies singly, in small groups, or more characteris- 

 tically in the form of bands, made up of two or 

 more parallel chains, which infiltrate the wall of 

 the ulcer. Large numbers are often found in the 

 polymorphonuclear leucocytes of the pus, par- 

 ticularly at an early stage of the lesion (Kraeft- 

 ing). Great difficulty was encountered in culti- 

 vating the bacillus, and Ducrey's first success was 

 obtained with a medium which contained human 

 skin. It has since been cultivated on agar which 

 contains the blood or serum of man, rabbit or 

 dog. Himmel attempted to cultivate it in the 

 fresh defibrinated blood of the guinea-pig, but 

 was unsuccessful because the bacilli were phago- 

 cytized by the leucocytes (Babes). 



An ulcer resembling that of soft chancre may 

 be produced in the ape, and also in the cat, by the 

 inoculation of pure cultures. Didey reinoculated 

 man, successfully, from the ulcers of the cat. 

 When living cultures are injected into the guinea- 

 pig (peritoneal cavity, subcutaneous tissue, dura 

 mater), the bacilli are quickly taken up by leuco- 

 cytes and digested (Himmel). Himmel reports 

 having so decreased the resistance of guinea-pigs 

 by peritoneal injections of lactic acid that' they 

 became susceptible to infection. After two or 

 three passages the culture became so virulent that 

 fatal bacteriemia was caused without previously 

 lowering the resistance of the animals. 



