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108 OUTLINES OF BACTERIOLOGY 



appearance of cocci, but, as it can be shown that in certain media 

 the individuals grow into somewhat elongated motile rods, the species 

 must be reckoned among the bacilli (Fig. 68). It grows on all kinds 

 of cooked food, particularly during the hot summer months, its growth 

 being easily distinguishable by the red colouring 

 ^ & matter which the organism excretes. When grown 



on potatoes' an unmistakeable smell of ammonia and 

 trimethylamine is produced. Very closely allied 

 to Bac. prodigiosus is Bacterium kiliensi, which is 

 commonly found on rotting fish. 

 digiosus!~sho'\Jiii g Bacillus fluorescens liquefaciens often occurs in 

 Engtba? differenfc abundance in decomposing matter. It is widely 

 distributed in nature, especially in the soil and in 

 polluted water. A culture of this species usually shows a beautiful 

 green fluorescence. The individuals are rod-shaped 1'5-6'0/z long and 

 0'4/z broad. The characteristics of this organism, by which it can 

 be identified, are the following : Green fluorescence, a strongly aerobic 

 nature, an incapacity to form spores, and a power of liquefying gelatine. 

 Sac. pyocyaneus is another of the chromogenic species which is very 

 commonly found in excrement, in polluted water, and in the soil. On 

 artificial media a growth is produced which possesses a yellowish-green 

 and a blue pigment. This species is suspected by many of being a 

 pathogenic variety of the harmless Bac. fluorescens liquefaciens. 



One of the most important of the saprophytic bacteria is Bacillus 

 coli communis. It is found as a normal inhabitant of the human 

 intestine and of the intestines of the lower animals. It is consequently 

 always present in dung and various kinds of excrement, and is the 

 commonest of the sewage-bacteria. A full description of this species 

 and its allies will be given in the chapter dealing with the bacteriology 

 of sewage. 



All the saprophytic bacteria hitherto mentioned are aerobic, but in 

 addition a large number of anaerobic bacteria 

 play an important role in the breaking up of 

 organic matter. The most important of these 

 is Bacillus putrificus (Fig. 69), which was dis- 

 covered in 1899. It is always present in 

 the soil, in decomposing dung, and in liquid 

 manure. Since its discovery it has been FlG . 69 ._ Bac . 

 isolated from a variety of different decom- 

 posing media, so that there is every reason to believe that it has a 

 very wide distribution. The bacilli are 5-6u long and 0'8/x broad, 



