32 



INHIBITORY ACTION OF PARATYPHOID BACILLI 



TABLE VII. 



Efect of Incubation of 5 Day Cultures of Paratyphoid Bacilli {Calf 297) Heated 

 at 62° C. for 35 Minutes on B. coli {Calf 302). 



DISCUSSION AND SUMMARY. 



Bacteria of the paratyphoid group may be divided into two classes 

 according to the behavior of 4 day cultures in lactose bouillon after 

 a second inoculation with certain types of Bacillus coli. One class 

 includes all true hog-cholera bacilli, the other nearly all true para- 

 typhoid and enteriditis types. Under the imposed conditions Bacillus 

 coli produces the usual amount of gas in the presence of the first group. 

 In the presence of the second no gas or only a bubble appears. The 

 production of acid is not interfered with. 



The significance of the inhibition was investigated in a variety of 

 ways suggested by the particular hypothesis entertained at the time. 

 Two main possibilities presented themselves; first, the direct associ- 

 ation of the inhibition with living paratyphoid bacilli, and, second, 

 the existence of a ferment or other product of growth as the inhibiting 

 agent. 



The theory that the living bacilli or those killed at the lowest 

 possible temperature are responsible was favored by a number of 

 experiments. Thus the complete removal of bacteria by filtration, 

 or by centrifugation combined with the use of kaolin to produce a 

 clear fluid restored gas production. The presence of a fine cloud of 

 bacteria was sufficient to inhibit. On the other hand, the addition of 

 large numbers of living bacteria from agar slants or from lactose 

 bouillon after the requisite incubation period to fresh lactose bouillon 



