THE BEAN BLIGHT: CULTURAL CHARACTERS 293 



growth in milk, filter the translucent fluid through coarse ster- 

 ile paper or sterile cheesecloth and divide it into two equal 

 portions a and 6: heat a for 20 minutes in the water-bath at 80°C. 

 and pour it into a test tube of sterile milk ; heat b for 20 minutes 

 at 50°C. (to kill the bacteria), streak on potato copiously to de- 

 termine that they have been killed, and pour into another test 

 tube of sterile milk. Add a small crystal of thymol to each 

 tube by means of sterile forceps. Watch the two closely for 

 the next 48 hours. The milk which received b should curdle in 

 the absence of the living bacteria, that which received a should 

 not curdle. How do you account for the difference? Observe 

 the tubes of inoculated litmus milk carefully from time to 

 time. Is there ever any acid reaction? Do not be deceived by 

 appearance of tubes when held up to the light; all litmus solu- 

 tions are red by transmitted light. Examine and decide only 

 by reflected light. 



Study growth in peptone bouillon; ditto in nitrate bouillon. 

 Are nitrates reduced? 



Behavior in Cohn's solution — in Uschinsky's solution. 



Growth in peptone water in fermentation tubes with various 

 sugars and alcohols. Compare with Bacterium campestre 

 and with Bacterium malvacearum, testing as many carbon com- 

 pounds as possible. 



Study effect of freezing (4-hour tube cultures in +15 peptone 

 beef bouillon in salt and pounded ice for one hour). In 1919 we 

 tried five isolations with the following per cents of killing: 

 Idaho, original stock, 87; Idaho, G. H., 98; Michigan, 99+ ; 

 New York, 89 ; Washington, D. C., 99+ ; Maryland, 99 + . Read 

 Science N. S., vol. XXI, No. 535, March 31, 1905, pp. 481-483. 



Is litmus reduced? Is indol formed? Ammonia? Carbon 

 disulphide? Invertase? Catalase? Pour some fresh hydrogen 

 peroxide into an old potato culture and observe the result. 

 What do you conclude as to the nature of the reaction? What 

 other ferments are formed? Nature and solvents of the yellow 

 pigment? Is it a lipochrome? 



Non-nutritional Environment. — Reaction to heat, frost, sun- 

 Ught, dry air, germicides. Behavior on media (use a variety) 

 in non-respirable gases — carbon dioxide, hydrogen, nitrogen. 



