38 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



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

 hydrate foods. 1 



Erwinia. 2 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. ERWINIA. FIG. 23. PROTEUS. 



and gas. Bacteria belonging to this group are among 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. 



2 This genus is variously incorporated by writers in plant path- 

 ology with the genus 'Bacterium or the genus Bacillus. 



