BACILLI IN WATER. 401 



germs in the cubic centimeter of ice- water. Distilled water 

 itself, after standing for some time, contains many water- 

 bacteria, but these are among those that do not bear 

 freezing. 



Artificial carbonated waters are often rich in bacteria, 

 even after standing for months, and it has been shown ex- 

 perimentally that typhoid-bacilli, for instance, may survive 

 for from days to weeks in such water. Care, therefore, 

 should be taken to prepare artificial waters only from pure 

 drinking-water or from distilled water. 



THE BACTERIA PRINCIPALLY FOUND IN SOIL, 

 AIR, AND WATER* 



L BACILLI, 

 i. NOT LIQUEFYING GELATIN. 



(a) Chromogenic. 



1. Bacillus Aurantiacus. This is a short, plump rod, with 

 slight spontaneous movement. Upon plates it appears in the 

 form of an orange-colored, knob-like deposit. In gelatin stab- 

 cultures it exhibits a glistening, orange-colored growth. Its 

 appearance in bouillon is characteristic. The fluid itself remains 

 clear, while upon the surface a membrane forms, presenting a 

 small number of orange-colored spots, and at the bottom a 

 somewhat lighter sediment collects. 



2. Bacillus Constrictus, This organism derives its name 

 from the peculiar appearance it presents when stained by the 

 method of Zimmermann. The rods exhibit a slight constriction 

 between the individual segments, which are united into short 

 chains, and they resemble biscuits in shape. In plates the colo- 

 nies present the appearance of granular discs, with eroded mar- 

 gins. The color is between yellowish-gray and light sulphur- 

 yellow. 



j. Bacillus Fluorescens Nonliquefaciens. This is a delicate, 

 short, actively motile rod. Upon gelatin the colonies present 

 a peculiar mother-of-pearl luster, which also exhibits fluores- 

 cence. Upon agar-agar the growth acquires a greenish tint. A 

 subvariety has been described as bacillus fluorescent nonliquefa- 

 ciens immobilis, which is distinguished by the absence of motility 

 and of flagella. 



4. Bacillus Fuscus. This is a medium-sized rod, sometimes 

 curved, which takes its name from the dark-brown pigment to 

 26 



