THEOBALD SMITH AND DOROTHEA E. SMITH 27 



tion, possibly a carbonate. Tube c checked the culture medium and 

 Tube d proved the absence of fermentescible sugars in the kaolin. 



Efect of Density of Suspension of Paratyphoid Bacilli. — In the fore- 

 going tests the primary culture was usually 4 days old before the 

 second inoculation was made. The mere presence of paratyphoid 

 bacilli in the culture fluid might have some influence irrespective of 

 any incubation period. Experiments were therefore undertaken to 

 eliminate this period. The growth of paratyphoid bacilli on slanted 

 agar was washed off with bouillon and suspended in lactose bouillon 

 in fermentation tubes. The suspension was varied in density by 

 using the growth of one, two, and four slants respectively. Immedi- 

 ately after the suspension was made a loopful of Bacillus coli was 

 introduced from an agar culture and the tubes incubated. The gas 

 production was not inhibited but it accumulated more slowly than 

 in control tubes. After 7 days incubation 70, 68, and 66 per cent of 

 gas had accumulated. The reaction of fluid in the bulb was 4.61, 

 4.96, and 4.91 per cent of a normal acid respectively. It should be 

 stated that the density of the suspension of paratyphoid bacilli, even 

 in the closed arm of the first tube, was much greater than that develop- 

 ing directly in lactose bouillon. No inhibition of gas production was 

 thus produced by the mere presence of large numbers of living para- 

 typhoid bacilU, both strains being introduced together. 



In another experiment, the relation of the bacilli to the inhibition 

 was put to a more rigorous test. A large centrifuge bottle containing 

 lactose bouillon and inoculated with paratyphoid. Calf 297, was 

 incubated for 6 days. One fermentation tube was then filled with the 

 culture fluid and inoculated with Bacillus coli, Calf 302, and incubated 

 as a control. Another lot from the same bottle was centrifuged until 

 the supernatant fluid was only faintly clouded. This fluid was trans- 

 ferred to a second fermentation tube and inoculated with Bacillus 

 coli. The thick bacterial sediment in the centrifuge tubes from 30 

 cc. of the culture fluid was transferred to 25 cc. of fresh lactose bouil- 

 lon in a fermentation tube and inoculated with Bacillus coli. Over 

 50 per cent gas was promptly produced in the third tube. In the 

 others a small bubble appeared partly derived from fine bubbles 

 transferred with the culture fluid. 



