CLASSIFICATION 871 



becomes obscured. Microscopically, the organisms are present in large numbers in the 

 local effusion and in much smaller numbers in the blood stream. Sporing forms are absent. 

 An even more typical picture of gas gangrene can be obtained by the injection of CI. welchii 

 intramuscularly into pigeons (BuU and Pritchett 1917a). Mice are less susceptible than 

 guinea-pigs. 



Pathogenicity of CI. septicum for Laboratory Animals. 



Intramuscular injection of about 0-1 ml. of a 36-hours' glucose broth culture into a 

 guinea-pig causes death in 12 to 24 hours. Post mortem, there is a blood-stained gaseous 

 oedema at the site of inoculation, spreading up over the abdominal wall, with collections 

 of gas in the groins and axillae. The thigh and abdominal muscles are soft and deep 

 red in colour. In the pericardial and peritoneal cavities there may be some fluid ; the 

 suprarenals are congested, but not so markedly as in animals infected with CI. welchii. 

 Microscopically the exudate shows large numbers of motile rods and usually the characteris- 

 tic navicular or citron forms. Most characteristic are the long curved filaments found on 

 the peritoneal surface of the liver. A similar picture can be reproduced by the inoculation 

 of mice. 



Pathogenicity of CI. oedematiens for Laboratory Animals. 



Intramuscular injection of about 1 ml. of a 24-hours' glucose broth culture into a 

 guinea-pig or mouse produces death in 1 to 2 days. Post mortem, the muscles at the site 

 of inoculation are very congested, purplish-red in colour, and infiltrated with small bubbles 

 of gas. There is a spreading, gelatinous oedema, sometimes slightly blood-tinged, extending 

 over the thigh. The abdominal muscles are unaltered. Microscopically, bacilli are found 

 in small numbers in the oedema fluid, and on the peritoneal surface of the liver : cultures 

 from the heart's blood may or may not be positive. 



It will be seen that the action of these last three organisms varies in certain 

 particulars. Gl. welchii gives rise to a large amount of gas, CI. oedematiens to very 

 little. The oedema fluid of CI. oedematiens infections is practically clear, of CI. 

 welchii infections slightly blood-tinged, and of CI. septicum infections strongly 

 ■blood-tinged. With CI. welchii the muscles are pale pink, with CI. oedematiens 

 purplish-red, and with CI. septicum intensely and deeply red. Human cases of gas 

 gangrene differ too in certain respects ; as a rule either oedema or, more rarely, 

 gas production is dominant ; occasionally both are apparent. The particular 

 form in any indi\ddual case is determined by the nature of the organisms present. 



Classification 



Although it is clear that the time is not yet ripe for any rigid classifica- 

 tion of the anaerobic bacilli, we can recognize certain well-differentiated types, 

 which should clearly be accorded specific rank. Table 56 presents a rough 

 classification of the organisms chiefly associated with gas gangrene and similar 

 infections in man, which were considered by the Anaerobic Committee of the 

 Medical Research Council (Report 1919) to be separate species. We may note, 

 however, that the characters differentiating CI. parasporogenes from CI. sporogenes 

 are hardly of sufficient importance to entitle it to classification as a separate species ; 

 it may prove on further investigation to be merely a variant of the latter organism. 

 Moreover the identity of CI. hutyricum with the organism originally described by 

 Pasteur seems to be very doubtful ; it is unfortunate that this organism has been 

 selected as the type species. In many respects it resembles CI. fallax and CI. multi- 

 fermentans. A few organisms have since been studied in sufficient detail to provide 

 an adequate description of their biological characters and to differentiate them 



