BACTERIA 47 



resisting twenty hours' boiling. "The spores germinate laterally. 

 The organisms of this group are typical soil bacteria, finding their 

 way into the soil from hay, potatoes and other feeding stuffs, in 

 which they were first found. With the dust, and from the excre- 

 ments of the stable, they find their way into milk, rendering it 

 very difficult to sterilise. Being obligate aerobes, they generally 

 form films on the surface of the culture solution and carry the 

 oxidation of carbohydrates almost to completion. They contain 

 diastase, which enables them to hydrolyse starch ; if bread con- 

 tains spores of these bacteria, which have not - been killed in 

 baking, it becomes slimy after a few days. They peptonise 

 actively, are Gram-positive and peritrich. The two best-known 

 species, Bacillus subtilis and Bacillus mesentericus, are best dis- 

 tinguished from one another by cultivation on potato slices, on 

 which the former produces a smooth film and the latter a wrinkled 

 film. Bacillus mycoides is most frequently found in incompletely 

 sterilised milk ; it forms stellate colonies like those of B. Zopfii, 

 in stab cultures, before the gelatine is melted. Bacillus anthracis 

 (Fig. 16A), grows similarly, but is non-motile. Most of the hay 

 and potato bacilli are thermophile, that is they are able to grow at 

 high temperatures, many of them growing well at 50 C., and some 

 even at 60 C. Other species actually prefer temperatures of 

 50 to 70 C., and do not grow at ordinary temperatures ; these are 

 often non-motile, and anaerobic rather than aerobic. When 

 masses of hay or other vegetable matter become warm, this is in 

 the first place due to the oxidation or respiration of the vegetable 

 matter itself, but when the temperature reaches 50 C. the vital 

 processes of the plant remains cease, and further production of 

 heat is due to the action of the thermophile bacteria until their 

 maximum temperature is reached. Further rise in temperature 

 and spontaneous ignition may take place owing to purely chemical 

 oxidation, i.e., combustion. 



B. Anaerobic Putrefactive Bacteria. All the organ- 

 isms of this group are peritrich spore-forming rods which 

 closely resemble the butyric acid bacteria, from which, how- 

 ever, they differ in being able to attack proteins. The most 

 important member is Bacillus putrificus which contributes more 

 than any other organism to the development of the putrefactive 

 odour ; it is able to grow in solutions of pure proteins. The 

 Plectridium foetidum, isolated by Weigmann l from cheese, which 

 produces in milk a smell like that of Limburg cheese, is, according 

 to Barthel 2 , identical with Bacillus putrificus. The author 3 has 



1 " Centralblatt f. Bakt.," 2 Abt., 1896, Bd. II., p. 150. 



2 " Centralblatt f. Bakt.," 2 Abt., 1910, Bd. XXVI., p. 1. * 



3 "Centralblatt f. Bakt.," 2 Abt.. 1904, Bd. XIII.. p. 754. 



