ORGANISMS OF SANITARY- SIGNIFICANCE ON GRAINS 211 



Gelatin plate. Thin, small, irregular colonies much as on agar. 



Gelatin stick. Nail growth; small, somewhat spreading colony at surface; 

 gelatin not liquefied. 



Agar plate. Surface colonies opalescent, nearly circular, edges smooth. Sub- 

 merged colonies clear cut, lenticular. After two or three days surface colonies take 

 irregular grape-leaf forms. 



Agar slope. Twenty hours: luxuriant, moist, opalescent, translucent, white 

 growth narrowing from top to bottom. 



Nutrient broth. Twelve hours: distinct turbidity; 18 hours: slight sediment; 

 after two days, no scum on surface. 



Litmus milk. Litmus reddened and then decolorized in from 12 to 18 hours; 

 milk coagulated; casein not redissolved. 



Potato. Luxuriant, dirty-yellowish growth, later becoming slightly slimy; potato 

 not discolored. 



Dextrose broth. Dextrose fermented in from 6 to 12 hours with formation of 



acid and gas. Gas ratio ^j- = - , but may vary even with the same stock. 



Saccharose broth. Fermented, with formation of acid and generally some gas' 



Lactose broth. Fermented; acid and gas formed; with less gas, but gas ratio 

 more constant than with dextrose broth. 



Maltose broth. Fermented, with formation of acid and gas; similar to lactose. 



Litmus lactose agar plate. Litmus reddened in less than 24 hours; bubbles 

 of gas formed. 



Dunham's solution. Growth, and pronounced nitroso-indol reaction in three 

 days. 



Anaerobic agar streak. Thin, transparent growth, somewhat less abundant than 

 in aerobic streak. 



Lactose neutral red broth. Gas formed and color generally reduced to canary- 

 yellow (not constant). 



METHODS OF ISOLATION USED. 



In the earlier experiments cultures of the bacteria examined 

 were obtained by making infusions of the grains in sterile water 

 and plating at once on litmus lactose agar without any preliminary 

 cultivation. Variable numbers of colonies were obtained, some of 

 which were of acid-producing bacteria. These red colonies were 

 then "fished," the masses of bacteria shaken up in sterile water and 

 replated on litmus lactose agar. From the typical isolated colonies 

 on this plate broth cultures were made, and after development 

 these were used as stock cultures for the inoculation of other media 

 viz., gelatin stab, litmus milk, agar stroke, dextrose broth, nitrate, 

 and Dunham solution. Hanging-drop preparations and stained 

 preparations were made from each culture, and by a comparison 

 of the reactions and morphological features with those of B. coli 



