INFECTIONS OF THE DIGESTIVE TRACT 171 



onset of symptoms. 1 The number of bacilli ingested 

 doubtless exerts an important influence on the character 

 of the illness. If few bacilli are associated with the 

 poison, they usually do not suffice to set up an infection, 

 and the seizure is transitory. If many bacilli are present, 

 they may establish themselves, freely multiply, and in- 

 vade the organism, causing the phenomena of typhoid 

 fever. Hence in a case where the poison present in 

 the food is associated with many paratyphoid bacilli, 

 the fever incidental to the intoxication may be directly 

 succeeded by a period of fever due to the bacillary in- 

 fection. Animal experiment teaches that in certain 

 virulent bacterial infections the period of incubation is 

 in a rough way inversely proportional to the number of 

 bacteria taking part in the infections. The ingestion of 

 very large numbers of paratyphoid bacilli may thus be 

 followed by a short period of incubation, whereas many 

 days may probably intervene before the onset of fever 

 if the number of bacilli barely suffices for them to gain 

 a foothold in the blood- vascular and lymphatic structures. 

 Although we have no definite information on this point 

 in the case of paratyphoid infection, it seems safe to 

 assume that the character of the anti-bacterial defenses 

 of the organism is a factor of equal importance with the 

 number of bacilli in determining infection. These con- 



1 Dr. Holt tells me it is common for typhoid fever in young 

 children to begin acutely. Probably the defenses of the digestive 

 tract against the bacilli are much feebler during infancy than in 

 later life, and an insult from an error in diet may injure these local 

 defenses so as to permit rapid and free multiplication of the typhoid 

 bacilli. 



