242 ESSENTIALS OF BACTERIOLOGY 



there is evidence of the presence of typhoid fever or diarrheal 

 diseases, the water should be boiled and subjected to careful 

 analysis daily. There may be serious contamination and 

 the chemical tests show no appreciable increase in the chlorids. 



Bile Media. In recent years bile salts or fresh bile mixed 

 with lactose have been extensively used, as the bile inhibits 

 the action of many bacteria and allows the colon and ty- 

 phoid group to develop readily. 



The Jackson bile media (see formula for media, Chap. X) 

 is placed in fermentation tubes of 40 c.c. capacity, and in- 

 oculated with varying proportions of the water to be tested. 

 Incubated at 37 C., and presence of gas looked for in twelve 

 hours, twenty-four hours, and forty-eight hours, and the 

 quantity and time noted. 



In sewage and contaminated waters the lactose-bile gives 

 better results than any other medium. 



The Presumptive Test (Modified). Plant T V, i, and 10 

 c.c. of water into liver broth tubes. Transplant from these 

 into lactose bile in six and twelve hours. By using implan- 

 tations of both lactose bile and liver broth, and then trans- 

 planting the liver-broth cultures into other lactose bile, we 

 have in the original bile the vigorous Bacillus coli. The liver- 

 broth dilutions give all the gas formers, strong and weak, 

 and the difference between the original and the transplanted 

 gives an idea of the attenuated Bacillus coli present. Thus 

 all the gas formers are cultured. 



Bacillus Typhosus. By the use of bile media and other 

 special media as enrichment and then transplanting on 

 Hesse Agar, Conradi-Drigalski, or Endo media, the Bacillus 

 typhosus are increased in number and the possibilities of 

 diagnosing them made much easier. The Widal test is 

 used to differentiate Bacillus typhosus from Bacillus coli. 



Quantitative Tests. The number of acid colonies in i c.c. 

 and in 5 c.c. of water is taken as a measure of pollution, to- 

 gether with the total number of colonies of all bacteria present. 

 Thus in i c.c. on the gelatin plate at 20 C. there may be 



