192 pathogenicity; chemotherapy 



muscle glycogen leads to localised pockets of acid, consequently 

 conditions are suitable for the production of histamine within 

 the wound. The histamine content of the muscles of a cat 

 may increase by 100-250 per cent, when CI. welchii infection is 

 established, but since it is not possible to demonstrate any 

 increase in the blood histamine, it is doubtful whether this 

 histamine production has any generalised effect. 



The three occurrences so far outlined are the result of the 

 simple metabolism of the organism and play their part in the 

 superficial characteristics of the disease and its clinical picture, 

 but are not seriously concerned in the lethal nature of the 

 infection. When infection with CI. welchii is accompanied 

 by contamination with either CI. sporogenes or CI. histolyticum 

 then these three factors so far discussed become exaggerated 

 as both these Clostridia are highly proteolytic. Consequently 

 their presence leads to a more rapid liquefaction of the tissues 

 with increased supply of amino-acids to the pathogenic 

 organism. 



4. Invasion of the tissues 



If a number of experimental infections of animals are made 

 with various strains of CI. welchii, it is found that whereas 

 some organisms establish themselves in the wound quickly, 

 penetrate the tissues, and set up a fulminating gas gangrene, 

 others, though of equal toxicity, are unable to establish 

 themselves or to penetrate the tissue. The strains are said 

 to vary in their invasiveness. Penetration of tissue by 

 bacteria is opposed by a barrier of highly viscous mucoprotein 

 between the tissue cells, and many organisms are unable to 

 penetrate such a barrier. Highly invasive organisms have the 

 power to decompose the polysaccharide portion of the complex 

 by the formation of an extracellular enzyme. The poly- 

 saccharide concerned in muscle tissue is called hyaluronic 

 acid and consists of equal parts of glucuronic acid and N-acetyl- 

 glucosamine. Some organisms excrete an enzyme called 

 " hyaluronidase," which is able to attack and decompose 

 hyaluronic acid. The chemistry of the breakdown is not yet 



