864 CLOSTRIDIUM 



basis of tteir gaseous metabolism. Growth in plain peptone water results in the 

 production of CO2 and Hg in difJerent proportions ; the CO2/H2 ratio is said to be 

 high with the proteolytic and low with the saccharolytic members. Thus for 

 CI. histolyticum it is over 91, for CI. sporogenes 36-9, for CI. bolulinum 18-3, for 

 CI. tetani 1-17, for CI. septicum 0-98, and for CI. welcJm 0-4. 



Litmus milk is a useful medium for differentiation (see Wolf and Harris 1917, 

 Weinberg and Seguin 1918, Wolf 1918-19, 1919-20, Report 1919, Anderson 1924, 

 Wagner et al. 1924). Spray (1936) introduced iron-litmus milk and iron-gelatin as 

 differential media, in which reactions with the iron, notably blackening of the 

 medium, provide several useful distinctive characters among Clostridia (see Table 57). 



It has been stated that none of the anaerobes is able to form catalase (Adamson 

 1919-20). This statement probably needs modification ; we have obtained evi- 

 dence of its production by CI. sporogenes and CI. histolyticum, though only in small 

 amounts. 



Antigenic Structure. — Antisera have been prepared against a number of 

 species, and agglutination and complement-fixation reactions have been carried 

 out. Difficulty has often been experienced in the preparation of stable suspensions ; 

 there is a great tendency for auto-agglutination to occur. The work of Felix and 

 Robertson (1928) showed that the motile species of anaerobes contained thermo- 

 labile H and thermostable antigens, similar to those described for so many of 

 the aerobic bacteria. It was thought that type specificity, as determined by 

 agglutination, was dependent on the H antigen, and group specificity on the 

 antigen. 



The more recent work of Henderson and others, however, seems to show that the 

 position is rather more complex. With CI. septicum, for example, Henderson (1934) finds 

 that the most convenient subdivision is made on the basis of the antigen. Though 

 there is considerable overlapping in different strains, there appear to be four specific 

 O receptors. These four primary groups can be further subdivided according to the type 

 of the H antigen. Henderson (1932) states that there is an O antigen common to the 

 ovine and the bovine strains of CI. chauvosi, but that the H antigen is complex, differing 

 to some extent according to the animal source and the country of origin of the strain 

 (see also McEwen 1926, Roberts 1931). The relation between CI. septicum and CI. chauvoei 

 is not very clear, but the work of Weinberg. Davesne, MihaUesco, and Sanchez (1929) 

 and Kreuzer (1939) suggests that the two organisms are closely related antigenicallj-. 

 CI. tetani is divisible into at least 10 types, all of which possess a common O antigen, 

 and a second antigen is present in Types I, III, VI, VII, VIII and X. Type specificity 

 depends on a flagellar antigen. CI. tetanomorphum has a minor somatic antigen in common 

 with CI. tetani (Wilsdon 1931, Gunnison 1937, MacLennan 1939). Attempts to form sero- 

 logical groups of CI. welchii have met with varying success. Test antisera usually react 

 fully with the homologous strain, and only with a few heterologous strains (Henriksen 

 1937, DuflFett 1938, On- and Reed 1940). There is some evidence that the four toxigenic 

 types (see below) differ in their bacterial antigens (Kreuzer 1939), but each type is anti- 

 genicaUy heterogeneous. Thus Henderson (1940) distinguished two kinds of somatic 

 antigen, a heat-stable O, and a heat-labile (L), antigen. He found strain-specific antigens 

 in Type A, but no L antigen ; 13 strams of Type B fell into two 0-antigenic groups, and 

 into 7 L-antigenic groups ; all his Type C strains had a common O antigen but no Lantigen ; 

 and there were various O and L antigenic groups in Type D. Rod well (1941) found a 

 similar variety of antigens in the four types. In CI. welchii the specificity of agglutina- 

 tion among S forms appears to depend on the nature of the capsular substance, which 

 contains polysaccharides. On the whole, the serological reactions of antigenic extracts 

 of capsular substance are as heterogeneous as the agglutination reactions of the bacilli 



