7O Elements of Water Bacteriology. 



be applied in water bacteriology. This consists of an 

 agar medium containing nutrose, sodium chloride, litmus, 

 lactose, and a dye, "crystal violet"; and it is used in the 

 form of plate cultures infected by smearing the surface 

 after thorough cooling with a bent glass rod. The cul- 

 ture medium is a selective one, ordinary saprophytes 

 failing to grow, while after fourteen to twenty-four 

 hours at 37 degrees, colon and typhoid colonies can be 

 readily distinguished from one another. The colon bacil- 

 lus produces red, non-transparent colonies, of variable 

 size and depth of color, while the typhoid colonies are 

 blue or violet, transparent, and of smaller size, seldom 

 exceeding three millimeters in diameter. 



Endo (Endo, 1904) has suggested the use of a fuchsin- 

 lactose-agar decolorized by sodium sulphite. Upon this 

 medium B. coli produces bright red, sharply denned, 

 round colonies in 24 hours at 37 degrees, while B. typhi 

 gives round, colorless, transparent colonies with thin mar- 

 gins. This medium has been somewhat modified by 

 Gaehtgens (Gaehtgens, 1905) by the addition of caffeine, 

 and he found it of great service in isolating the typhoid 

 bacillus from stools of patients suffering with the disease. 

 No attempts were made by him to isolate the organism 

 from polluted water. 



LoefBer (Loeffler, 1903 and 1906) and Lentz and 

 Tietz (Lentz and Tietz, 1903 and 1905) have made use of 

 an agar medium containing malachite green. This 

 medium is supposed to inhibit the growth of B. coli 



