QUALITATIVE DETERMINATIONS 93 



The real source of danger lies in the fact that the intestinal bacteria 

 normal to man and the lower animals, may be and frequently are 

 associated with pathogenic bacteria, such as the typhoid bacillus 

 and the dysentery bacillus. Our long experience with the con- 

 sumption of sewage contaminated water supplies, has shown that, 

 as a rule, the first danger sign of the excessive contamination was 

 usually a marked increase in the number of cases of dysentery, 

 generally followed by sporadic cases and epidemics of typhoid 

 fever. 



The practical results of the quantitative bacterial determi- 

 nations of food substances combined with the qualitative tests 

 for the colon group, has proven of the highest value and it is 

 considered entirely feasible to continue the application of the 

 tests and to suggest ways and means of improving the laboratory 

 technique covering such methods. The qualitative methods 

 thus far worked out are based upon a knowledge of the life history 

 of the bacteria concerned and may be briefly stated as follows: 

 Normal intestinal bacteria and such other bacteria as may develop 

 in the intestinal tract, such as the typhoid bacillus, the cholera 

 bacillus, the dysentery bacilli, etc., are adapted to a temperature of 

 about 37 C. and they feed upon the food materials found in the 

 intestinal tract and have a somewhat reduced oxygen supply. 

 Among the substances peculiar to the intestinal tract we find bile, 

 pancreatin, and other enzymes and a certain water percentage and 

 the various ingredients of food materials more or less digested 

 and the various products elaborated by the different species and 

 varieties of bacteria present. It is a study of the peculiarities of 

 the intestinal bacteria which has suggested the technique for 

 their isolation and their quantitative as well as qualitative esti- 

 mation in food supplies, as can be seen readily from a study of 

 the culture media and cultural methods recommended. To 

 enter into any fuller discussion of the work done by American and 

 European investigators on the bacteria which are normal to the 

 intestinal tract or which may occur in the intestinal tract in 



