t 



Factor in the Mechanism of Bacterial Infection. 521 



tetanus. As stated in the introduction, we have not been able to obtain 

 experimental evidence in support of this view in the case of gas gangrene by 

 injecting the bacteria of gas gangrene together with other bacteria which are 

 likely to form concomitant infectious in wounds. And even in the produc- 

 tion of tetanus from the spores by means of the toxin of B. Welchii, it must 

 be remembered that this does not represent the effect produced by a con- 

 comitant infection with the bacilli of Welch. For such an infection does not, 

 as we have seen, lead to the production of toxin sufficient to paralyse the 

 defensive mechanism. It still requires to be demonstrated that tetanus will 

 result when the spores of tetanus are injected together with the detoxicated 

 bacteria of Welch. 



The preceding considerations emphasise the importance of the contamina- 

 tion of the wound with earth from the point of view of the etiology of gas 

 gangrene and of tetanus. For this contamination carries into the wound not 

 only the infecting bacteria, but also frequently the chemical constituents of 

 the soil capable of producing the phenomenon of defence-rupture. But there 

 is also some experimental evidence to show that tetanus and gas gangrene 

 may sometimes develop even without the intervention of the phenomenon. 



071 the Mode of Action of Calcium Salts. 



Two possible explanations suggest themselves at once : the calcium salts 

 may produce their effect either by making the bacteria more virulent, or by 

 making the animal more sensitive to the action of the bacteria. Both these 

 possibilities were tested experimentally. 



In order to see whether there is a direct action on the bacteria, B. Welchii 

 freed from toxin were suspended in a solution of calcium chloride and 

 incubated for three hours. The suspension was then centrifuged, and the 

 bacteria after washing with saline suspended in a sodium chloride solution, 

 and the suspension injected into mice. Xo effect was produced. 



The same negative result was obtained when B. Welchii were incubated 

 for 20 hours in a broth culture to which some calcium chloride solution 

 had been added. A suspension of B. Welchii in saline prepared from such a 

 culture was incapable of producing gas gangrene. It is clear, therefore, that 

 calcium salts do not act directly on the bacteria in such a way as to render 

 them capable of producing gas gangrene by themselves in the absence of a 

 toxin. Nor does the addition of calcium chloride to a broth culture increase 

 the amount of toxin produced. This was demonstrated botli for B. Welchii 

 and for Vibrian septiq^te. It was however noted that the rate of growth of 

 £. Welchii and of Vilrion septique was much more rapid after the addition of 

 calcium chloride. It was further found that a culture of B. Welchii or 



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