THEOBALD SMITH AND DOROTHEA E. SMITH 33 



failed to inhibit gas production when Bacillus coli was added simul- 

 taneously. 



When the inhibiting culture was heated at 62°C. for 35 minutes to 

 sterilize it, gas production was still largely inhibited. But it was 

 restored when higher temperatures were used, completely at 100°C. 

 and above. It was also gradually restored by exposing the heated 

 culture to 37°C. for 3 or more days. 



The presence of variable amounts of lactose, or even the complete 

 absence of lactose did not interfere with the development of the 

 inhibitory factor. 



The activity of the inhibition factor presents itself in the form of 

 a curve, beginning at when both paratyphoid and colon bacilli are 

 inoculated simultaneously and rising as Bacillus coli is inoculated 

 at longer intervals from the paratyphoid bacilli. The maximum of 

 inhibition is reached at about the 4th day; thereafter it remains at 

 the same level for a few days and then gradually falls until it is lost 

 within 3 or 4 weeks. The curve of the hog-cholera group is delayed 

 in that the maximum inhibition is reached at the end of 3 weeks. 

 These curves have not' been accurately determined. Taking into 

 consideration all the accumulated data the writers tentatively pre- 

 sent the hypothesis that the inhibitory factor is some metabolic 

 product of the paratyphoid bacillus, possibly an enz^Tne, which is 

 destroyed at a temperature somewhat above the thermal death point 

 of the bacilli and which more gradually disappears from incubated 

 cultures. The substance fails to pass Berkefeld filters. It is carried 

 down mechanically with substances clearing the culture fluid. 



The experiments support current theories which hold that the acid- 

 producing and gas-producing entities in cultures are distinct. 



