194 pathogenicity; chemotherapy 



which interfere in some way with the essential metabolism 

 of the host ; (6) that they act in some other way by blocking 

 an essential activity in the host. 



MacFarlane and Knight have shown that preparations of 

 the a-toxin possess the activity of a lecithinase, and that during 

 purification, increase of toxicity is paralleled by increase of 

 lecithinase activity so that the purest preparations of toxin 

 are also the most active lecithinase preparations. 



Lecithinase hydrolyses lecithin with the liberation of 

 phosphocholine: 



Lecithin is an essential component of the membrane of cell- 

 walls, so that if the lecithin is decomposed, then the cell-wall 

 disintegrates. If the lecithin of the cell-wall of a red blood 

 corpuscle is hydrolysed, then the cell-wall disrupts and the 

 red cell haemolyses. In the same way tissue cells disintegrate, 

 and it is only reasonable to suppose that such a reaction, taking 

 place generally throughout the body, would be lethal in its 

 final effect. It is highly probable that the a-toxin of CI. 

 ivelchii is actually a very active lecithinase. Both a-toxin 

 and lecithinase are inactive in the absence of calcium ions, 

 and the lecithinase activity of the preparations is inhibited 

 by the specific antitoxin. 



The chemical action of the ^-toxin has not yet been dis- 

 covered. It also acts on some substance in the wall of the 

 red blood cell in a way that leads to disintegration but, 

 assuming that it is likewise an enzyme, its substrate has not 



