TOXIN PRODUCTION 189 



and phagocytose the invading organisms. If the toxin 

 production is sufficiently powerful or the bone-marrow response 

 too slow, then the toxic action may cause the death of the 

 host as in Case 3. If the toxin production is moderate and 

 the bone-marrow response adequate, then the initial advantage 

 given to the organism by its toxin production is overcome and 

 the invading cells eventually removed (Case 2). If the 

 invading cells are avirulent or saprophytic and produce no 

 toxin, then the reticulo-endothelial system is able to sterilise 

 the host's tissues without difficulty (Case 1). 



A pathogenic organism differs, then, from a non-pathogen 

 in that it possesses the power to produce a toxin, enabling it 

 in some way or other to gain an advantage over the defence 

 mechanisms of the host. This is not the sole property 

 necessary to produce a successful pathogen, as the property 

 of forming a toxin cannot be effective until the organism has 

 actually invaded the host's tissues. Consequently a second 

 factor of pathogenic importance is the degree of '' invasive- 

 ness," or capacity to penetrate the host's tissues. 



" Toxin " and " invasiveness " are names of two properties 

 of a pathogenic organism that can be more correctly described 

 in chemical terms. This branch of bacterial chemistry is one 

 which is only now being developeci, and has not as yet reached 

 a stage where generalisations can safely be made. Conse- 

 quently we shall take a specific case of disease causation, 

 namely, the production of " gas gangrene " by the infection 

 of a wound with CI. welchii, and endeavour to explain the 

 pathogenicity on a chemical basis. This disease is chosen 

 as example as it has been very intensively studied in recent 

 years, so that we now understand more of the chemical nature 

 of the pathogenic action of CI. welchii than of any other 

 organism. 



BIOCHEMISTRY OF GAS GANGRENE 



Gas gangrene is the name given to the clinical condition 

 following the infection of tissue, usually through a wound, 

 with CI. welchii and certain related strict anaerobes. It is 



