472 PATHOGENIC MICROORGANISMS 



There has been endless confusion in the classification of the so- 

 called aerogenes capsulatus organisms, a group which has been known 

 in different countries by a large variety of names. Its first description 

 is probably that by Welch and Nuttall 1 in 1892, who gave it the name 

 B. aerogenes capsulatus, by which name, or briefly Welch bacillus, it is 

 most commonly designated by American bacteriologists. Similar or 

 identical organisms are ttie B. phlegmonis emphysematosce of Fraenkel, 

 the B. enteriditis sporogenes of Klein, the B. perf ring ens of Veillon and 

 Zuber, and the Granulobacillus saccharobutyricus liquefaciens immobilis 

 of Schattenfroh and Grassberger, and a number of others less prominent 

 in the literature. 



The task of classifying these various organisms is one of great 

 technical difficulty, and, as in so many other groups of bacteria orig- 

 inally described as a single species, we are now learning that instead 

 of complete identification of individual isolations, one with another, 

 we can merely draw a circle about a certain group, recognizing close 

 relationship morphologically, culturally, and in relation to infections of 

 man and animals. After a very careful study of many different strains, 

 Simmonds comes to the conclusion that the Welch bacillus, so-called, 

 is roughly identical with those mentioned, including also the bacilli once 

 associated by Achalme with rheumatic infections. The term B. Welchii, 

 he concludes, does not represent a fixed species but a closely related group 

 of bacteria not yet fully classified even by his own extensive studies. 



It is often hard to determine in the case of organisms of such varied 

 activities exactly what can be regarded as a cardinal characteristic 

 important for classifying purposes. The organisms treated of in this 

 group are all large Gram-positive, non-motile bacilli, with rounded 

 ends, rarely occurring in chains, and anaerobic. Spore formation is in- 

 constant and occurs only in an alkaline medium. When fermentable 

 sugars, and consequently free acid, are present, no spore formation 

 takes place. Milk is fermented with the formation of butyric acid. 

 The intravenous injection of animals, especially rabbits, usually pro- 

 duces death with an enormous swelling of the body by the formation 

 of gas, which burns with a pale blue flame. Capsules may be seen 

 when the smears are made directly from animal tissues, but are almost 

 universally missed in organisms taken from culture. 



As to minor cultural characteristics, so many variations are ob- 

 served that it is hardly worth while to summarize them. 



1 See Simmonds, Monographs of the Rockefeller Institute, No. 5, Sept. 27, 1915. 



