236 JOHN T. MYEKS 



possible. The total forty-eight hour 20°C. bacterial count on 

 standard agar, the total forty-eight hour 37°C. bacterial count 

 on standard agar, and the colon count, using the complete test 

 fermentation tube method, were made in each case (A. P. H. A. 

 Committee, 1912, 1917). In the fermentation tube work, ten 

 tubes of lactose broth were inoculated with 1 cc. each of the 

 dilution selected and several dilutions were always used in order 

 to make sure that some one series of ten tubes would show gas 

 in only part of the tubes. All media were prepared according 

 to the standard method of water analysis of the American 

 Public Health Association (1912, 1917). 



The colon count was also made in each sample by plating on 

 Endo medium and counting the colon like colonies directly. 

 This was done as a check on the fermentation tube method and 

 to test the possibility of making direct counts of the colon con- 

 tent of sewage and other materials by the use of Endo medium. 



Table 1 indicates the types of feces studied and the data 

 obtained. 



The counts are expressed in millions and fractions of millions 

 in order to make the table less bulky. Table 1 indicates that 

 there is a fairly definite relationship between the amount of fecal 

 material in a given solution and the amount of hydrogen sulphide 

 formed, although occasional irregularities appear. 



There were some difficulties in making a colon count directly 

 on Endo medium, the most important being that deep colonies 

 are at times difficult to differentiate. On the whole it would 

 seem that the method is as accurate as the fermentation tube 

 method and it is perhaps less cumbersome, especially when 

 dealing with material that is heavily loaded with colon bacilli. 



Table 2 gives the minimum number of colon bacilli which 

 produced a perceptible blackening of the lead acetate paper after 

 incubation at 37°C. for twenty-four hours, forty-eight hours, 

 and seven days respectively. It also gives the twenty-four hour 

 37°C. count, and the forty-eight hour 20°C. count for purposes of 

 comparison with the colon count. The customary 90 cc. dilu- 

 tion was used. 



