and Laboratory Methods. 



197' 



laborator}^ window in the winter is not a favorable spot for plant life ; and the 

 difiference between the two pots is sufficiently well marked for demonstration. 



It is easy to obtain pure cultures of the nitrogen fixtures. The nodules are 

 cut out from the rootlets, sterilized in the same way as explained for the seeds, 

 pulverized, and the fragments plated out in gelatine. In 4 or 5 days the round 

 non-liquefying colonies appear and can be transplanted. The bacilli will grow 

 on ordinary media, but a specially favorable one is that recommended by Maze. 

 (Ann. Pasteur, 1897, '98, '99.) 



Allow 100 grams dry weight of beans to germinate on moist cotton for two 

 or three days, make an infusion of them in 1000 c. c water at 100°C. for 30 

 minutes; strain through cloth, add }^2 per cent. NaCl, and neutralize. Boil one 

 hour, filter, and add 3 per cent, of saccharose. The liquid comes out fairly 

 clear and can be used as broth or can be made up with Id per cent, gelatine. 



On bean gelatine slants the bacteria grow in great profusion, and according 



Fig. 



-Left. — Alfalfa Grown in Sterile Sand. Right. — Same with Cultures 

 of Nitrogen Fixers. 



to Maze they are able to fix nitrogen under these conditions, but this has not 

 been tested by us for confirmation Most investigators have been unable to get 

 the bacteria to fix nitrogen in artificial cultures. 



In the lecture attention is drawn to the fact that there is a constant accession 

 of dead animal and vegetable matter to the soil, and this is disposed of by bac- 

 teria ; the final products of the carbo-hydrates being gases and water, and of the 

 nitrogenous substances, gases, water, and nitrates, the latter remaining in the soil. 



In the course of explanation the following table is built up on the board : 



