THEOBALD SMITH AND DOROTHEA E. SMITH 31 



centrifuge bottle was transferred to fermentation tubes after 7, 24, 

 and 32 days and then inoculated with Bacillus coli, Calf 302. The 

 7 day culture inhibited gas formation completely, the 24 day culture 

 developed 44 per cent gas, the 32 day culture 35 per cent. The three 

 tubes developed the usual amount of acid. In another experiment a 

 culture of paratyphoid bacilli 22 days old yielded after inoculating 

 with Bacillus coli 13 per cent gas. It is probable that the inhibition 

 produced after 18 days by the hog-cholera bacillus is gradually lost 

 later on, but no experiments have been made to test this assumption. 



The Effect of Killing Paratyphoid Bacilli by Heat on Inhibition of Gas 

 Production by Bacillus coli. 



The results of the various experiments made thus far led to a study 

 of the behavior of dead bacilli on gas production. Numerous experi- 

 ments were carried out with a variety of controls in each but the 

 results were not entirely concordant and pointed to some neglected 

 factor. In all cases the exposure to temperatures which failed to 

 kill the first culture failed to destroy inhibition. After the thermal 

 death point had been reached the results became irregular, but the 

 experiments all agreed in that inhibition was destroyed as the tempera- 

 ture rose and at 100°C. and above gas production was more or less 

 completely restored. A careful analysis of the details of the experi- 

 ments which are not reproduced here led to the hypothesis that mere 

 death of the first culture is not sufficient to destroy inhibition but 

 that there is another factor involved which disappears rapidly on 

 exposure to high temperatures or gradually at lower incubator tem- 

 peratures. To demonstrate the gradual disappearance of inhibition 

 the experiments given in Table VII were made. Cultures of para- 

 typhoid bacilli in lactose bouillon contained in large centrifuge bottles 

 were exposed to 62°C. for 35 minutes. Subcultures were made at 

 once and after 1 or more days of incubation to determine whether 

 any bacteria had survived. The culture fluid was transferred to fer- 

 mentation tubes at once and after the heated fluid had been incu- 

 bated for 1 or more days. Subcultures were made at each transfer 

 to determine steriUty. 



