Factor in the Mechanism of Bacterial Infection. 



519 



the relation of the contamination of the wound with earth to the etiology of 

 tetanus, and whose observations as to the inadequacy of the nidus theory 

 agree in many respects with ours, recognised that this contamination exercises 

 a specific influence. But he ascribed this specific factor to the presence of 

 other micro-organisms in the earth. 



Of the various foreign bodies tested by us, emulsions of earth were the 

 only ones which frequently, although not invariably, elicited gas gangrene 

 when injected together with the detoxicated bacteria of gas gangrene or their 

 spores. That the effect of earth is not due to its mechanical action but to a 

 chemical constituent of the earth was demonstrated by the following experi- 

 ment : A sample of earth was taken which, when autoclaved and made 

 into an emulsion, would elicit gas gangrene from the spores of Vihrion 

 septique. The watery extract of such an emulsion, after having been filtered 

 through filter paper, autoclaved and tested for its sterility, was just as capable 

 of eliciting gas gangrene as the original emulsion. It could be shown, 

 moreover, by qualitative chemical tests, that this earth extract contained 

 calcium salts and that it lost its power to elicit gas gangrene when these salts 

 had been removed by precipitation with sodium carbonate. We are not 

 however prepared to state that the calcium salts in the soil are the only 

 chemical constituents which are responsible for this phenomenon, for some 

 extracts of earth which were capable of eliciting gas gangrene from the 

 spores of Vihrion septique contained only traces of calcium salts. It seems 

 probable that some other chemical substance present in these extracts, which 

 also forms an insoluble carbonate, is also capable of producing the kata- 

 phylactic phenomenon, and may be even more powerful in this respect than 

 calcium salts. Further investigations on this point are being carried out. 



It is of interest to note that samples of earth taken from the surface may 

 fail to show this effect when a sample from the same locality about 6 inches 

 below the surface will give a positive result. It has also been found that 

 samples from different localities differ in their activity, and that samples 

 taken from the same locality and from the same depth may show differences 

 at different times of the year, i.e., according to the treatment, such as 

 " liming," which the soil has received. These differences may not exhibit 

 themselves qualitatively by the presence or absence of the power to elicit gas 

 gangrene or tetanus, but quantitatively by the doses of earth extract or 

 emulsion necessary to produce this effect. These observations account 

 satisfactorily for the curious fact that the occurrence of gas gangrene on the 

 Western Front was very " patchy." It varied with the locality in which the 

 wounds had been received, and was relatively infrequent in certain localities, 

 even although the wounds were infected with the bacteria of gas gangrene. 



