66 BACTERIOLOGY. 



contact. It lasts from seven to ten days, and fre- 

 quently is attended with a death rate of from 5 to 20 

 in 100. 



Numerous epidemics have been reported in the 

 United States; among them, an epidemic of 350 cases 

 in the village of Tuckahoe, N. Y., which was studied 

 by the writer, together with Dr. Wm. H. Park. The 

 cause of the epidemic was found to be due to an or- 

 ganism almost identical with the one described by 

 Shiga. From a study of the dysentery bacilli found 

 in this and other epidemics in this country, we find 

 that there are a number of bacilli very nearly alike 

 that may cause these epidemics of dysentery. 



Individuals that have been infected with dysen- 

 tery bacilli develop agglutinating substances in the 

 blood that will clump the dysentery bacilli just as in 

 the case of typhoid and paratyphoid infections. 



To summarize what has been said of the colon- 

 typhoid-dysentery group: All the members are bacilli 

 of similar appearance, all are to some degree motile, 

 but they differ one from another in their manner of 

 growth, particularly in their ability to ferment sugars. 

 The colon group, although a constant inhabitant of 

 the intestine, gives rise to no infection unless it gains 

 access to tissues outside the bowel. The typhoid and 

 dysentery bacilli are never present in the body under 

 normal conditions, but when they enter the body they 

 cause a characteristic infection. The blood-serum of 

 all infected individuals develops substances that pro- 

 tect against reinfection, and among these substances 



