Factor in the Mechanism of Bacterial Infection. 



527 



injection of the bacteria together with toxin. The whole field is covered 

 with densely packed bacteria which are almost all gram-positive. Only very 

 few leucocytes can be seen, and none of these show any phagocytosis. 



Bach. R. Flank. 



Site of inoculation of B. Welchii. Site of inoculation of Ca salts. 



I 1 ' 



50^. 



Fig. 1. — Films from the back and right flank of a mouse which developed gas gangrene 

 and died 24 hours after having received fir.st 10 mgrm. of CaCla in the right flank, 

 and 2 hours later a suspension of B. Welchii in saline on the back. Stained with 

 gram and neutral red. Gram-negative staining is indicated by merely outlining 

 the bacteria. 



Both macroscopically and microscopically the picture presented by the right 

 flank is that of an animal which has succumbed to the B. Welchii infection ; the 

 picture presented by the back that of an animal which is successfully defending 

 itself against such an infection. 



This apparently paradoxical result becomes clear in the light of the con- 

 ception that the calcium salts produce at the site of their injection a local 

 change in the tissues which has as its ultimate effect a local breaking down 

 of the defensive mechanism. This conception of the mechanism is expressed 

 by the terms " defence rupture " or " kataphylaxis," with which we have 

 designated this phenomenon. 



When calcium salts and bacteria are injected together it is quite possible 

 that this effect may be assisted by other factors. There may be a direct 

 favouring effect of the calcium salts on the rate of growth of the bacteria, 



