38 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



This is found to cause red spots in bread and other carbo- 

 hydrate foods.^ 



Erwinia. = — The organisms belonging to this genus all 

 produce disease in plants. Their growth in the laboratory 

 is usually whitish. They form acids in certain carbohy- 

 drates, but as a rule no gas. One of the most important 

 species is Erwinia amylovora, the organism causing pear 

 blight. 



Proteus. — The organisms belonging to this genus are 

 highly pleomorphic rods, frequently producing filaments 

 and curved cells as involution forms. They are Gram- 

 negative and actively motile. Upon suitable culture media 

 they form amoeboid colonies. The organisms ferment glu- 

 cose and sucrose but not lactose with the formation of acid 



Fig. 22. — Ekwinia. Fig. 23. — Pkoteus. 



and gas. Bacteria belonging to this group are Eimong the 

 most important causes of putrefaction and decay. They 

 have been occasionally found associated with disease. 



Bacterium. — The organisms belonging to this genus are 

 Gram-negative rods, frequently motile, and easily cultiva- 

 ble. Most species ferment certain carbohydrates with the 

 formation of acid and frequently of gas. They are typi- 

 cally intestinal parasites in man and higher animals. Some 



1 Another genus belonging to this family is Chromobacterium in 

 which the cells produce a violet or blue pigment. 



2Tliis genus is variously incorporated by writers. in plant path- 

 ology with the genus'Bacterium or the genus Bacillus. 



