TOXIN FORMATION 866 



(Meisel 1938, Orr and Reed 1940, Svec and McCoy 1944). The S — > R variation in CI. 

 welchii is accompanied by a loss of specific O antigen (Henderson 1940). 



CI. bolulinum is divisible into seven groups according to the flagellar antigens, and 

 the proteolytic strains appear to possess a connnon O antigen (Schoenholz and Meyer 

 1925, McClung 1937). 



Among the proteolytic species we may note that CI. sporogenes can be divided into 

 at least two groups. Serological tests have been useful in resolving some problems of 

 identity of various species. Thus it appears from the work of Clark and Hall (1937) 

 and Stewart (1938) that CI. sordellii may be considered as a variety of CI. hifermentans. 

 (For other examples, see the review of McCoy and McClung 1938). One of the more 

 interesting results of serological study is the confirmation of a cultural and biochemical 

 relationship between R variants of CI. histolyticum and CI. sporogenes (Smith 1937, Hooger- 

 heide 1937) ; its significance is not clear. 



Toxin Formation. — It is remarkable that, with the exception of the diphtheria 

 bacillus, the organisms forming powerful exotoxins belong almost entirely to the 

 group of anaerobic spore-bearing bacilli. Two of them — CI. hotulinum and CI. 

 tetani — give rise to toxins more poisonous than any other substances with which 

 we are acquainted. It has been calculated that the most powerful toxin of CI. 

 tetani would kUl a man in a dose of 0-25 mgm., and of CI. botulinum in a dose of 

 0-0084 mgm. 



The formation of a powerful exotoxin does not appear to be associated with 

 the proteolytic activity of the organism. Soluble diffusible toxins have been 

 described in only two proteolytic species, CI. bifennentans and CI. histolyticum. 

 Whether the toxins are formed intra- or extra-cellularly is still unknown. Stark, 

 Sherman, and Stark (1928) have found that, if bacteria-free filtrates of CL botulinum 

 are added to sterilized skim milk in suitable proportions and incubated for 4 days 

 at 37° C, a considerable increase in toxicity occurs, suggesting that enzymes 

 present in the filtrate have formed fresh toxin from some constituent of the milk. 

 A number of clostridial toxins resemble the diphtheria toxin in that they can be 

 detoxified by formaldehyde with the formation of an antigenic toxoid that can 

 be used for active immunization (see Chapters 77, 78). The preparation of these 

 toxins requires attention to a number of factors with which we have no space 

 to deal. But their properties are important, and must be considered briefly. It 

 should be emphasized that many of the properties described are those of toxic culture 

 filtrates, not of isolated substances. Filtrates from cultures of CI. welchii, for 

 example, have been resolved into a number of components, and it is probable 

 that other " toxins " hitherto referred to for convenience as single substances will 

 prove to be mixtures. 



Tetanus Toxin. — This varies in potency ; a good filtrate will kill a mouse in 

 a dose of 0-00001 ml. It is destroyed by heat at 65° C. for 5 minutes, but if dried 

 it will resist 120° C. for 1 hour. Exposure to 55° C. for 1 hour is said to destroy the 

 greater part of its toxicity, while having little effect on its antitoxin-combining 

 power (Tschertkow 1929). It is destroyed by direct sunlight in about 15 hours at 

 40° C. ; exposure to diffuse daylight results in a gradual weakening of the 

 toxin. If precipitated with ammonium sulphate, dried over siilphuric acid, ground 

 to powder, and preserved in the dark at 5° C. in vacuum tubes under phosphorus 

 pentoxide, the toxin will remain unchanged for 2 years or more. 0-55 per cent. 

 HCl, 0-3 per cent. NaOH, and 70 per cent, alcohol each destroy the toxin in 1 hour. 

 The toxicity can be modified by iodine trichloride, by formol and (Velluz 1936) 

 by carbon disulphide ; these reagents are used in serum institutes for weakening 



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