THEOBALD SMITH AND DOROTHEA E. SMITH 



25 



Experiments to Determine the Nature of the Inhibition. 



The Effect of Removing the Paratyphoid Bacilli. — The first suggestion 

 to present itself was that the paratyphoid bacilli might have changed 

 the lactose in some way. If so, in the bouillon deprived of the para- 

 typhoid bacilli by filtration the colon bacilli should act differently 

 than in fresh bouillon. It was found, however, that the complete 

 removal of paratyphoid bacilli from the culture fluid by passing it 

 through a Berkefeld filter restores gas production. The experiments 

 were made by growing the paratyphoid bacilli in large centrifuge 

 bottles and filtering after centrifuging. The filtrate was put into 

 sterile fermentation tubes and inoculated with Bacillus coli. Table 

 I gives some of the results. 



TABLE I. 



The next step was to proceed as in the former experiment but to 

 omit the filtration. The centrifuged fluid did not become entirely 

 clear and when inoculated with Bacillus coli only a very little gas 

 was produced. Apparently the presence of a very faint cloud of 

 paratyphoid bacilli was sufficient to inhibit almost completely gas 

 production by Bacillus coli. The hog-cholera control treated in the 

 same way did not inhibit gas production (Table II). 



In order to remove as far as possible all bacteria without sub- 

 jecting the culture fluid to final filtration, the following procedure 

 was carried out. The primary culture was conducted as in the fore- 

 going experiment in large centrifuge bottles, holding 250 cc. and 

 plugged with cotton wool. After an incubation of about 4 days suf- 

 ficient to jdeld a maximum multiplication a certain quantity of sterile 

 kaolin powder was added to the fluid, the bottles were closed with 



