664 THE NODULE ORGANISM OF THE LEGUMINOS.E, 



Ordinaiy acid potato forms an excellent medium for its growth, 

 and yet it refuses to grow upon a medium prepared by adding 

 2 per cent, starch and 2 per cent, agar to acid potato extract. 

 The failure of the organism to grow upon this medium cannot be 

 due to the acidity, for the steamed potato and the potato-agar 

 had about the same acidity. It is moi'e probable that starch is 

 not the carbohydrate in the potato that is utilised, and that in 

 the nodule the organism does not utilise the starch as such. 

 Steaming possibly alters some of the relatively great amount of 

 starch in the acid potato into a derivative, which can supply the 

 organism with carbohydrate food. This derivative cannot be 

 dextrin, for experiment showed that when dextrin is added to 

 ordinary meat-agar to the extent of 5 per cent, it retards the 

 growth. Extract of lupins or of other leguminous plants does 

 not seem a necessity for the culture media. Grass will do quite 

 as well, and for that matter the plant extract might be left out 

 entirely. Fairly luxuriant cultures were obtained upon a medium 

 made with 10 per cent. Avashed gelatine, 3 per cent, glucose, and 

 the customary calcium chloride and potassium phosphate. The 

 most luxurious growth was obtained with meat-agar containing 

 6 per cent, glycerine. More than this percentage of glycerine, 

 e.g., 10 per cent, or 20 per cent., prevented growth. 



With regard to temperature, the organism grows very well at 

 22° C, and this is very fortunate since it enables gelatine media 

 to be employed. At 30° C. growth is slow, but it is by no means 

 checked. Maze was able to accustom the organism to grow at 

 35° C. 



The media ultimately adopted were peptone-glucose as a fluid 

 (see footnote, p. 661), and glucose-glycerine agar or gelatine as a 

 solid.* 



* Washed gelatine, 20 grams, or washed agar, 2 grams ; lupin extract, 

 100 c.c. ; glucose, 4 grams; glyceriue, 2 grains. Heat until tlie gelatine 

 or agar is dissolved, add 10 c.c. each of 10 per cent, monopotassium 

 phosphate and 20 per cent, calcium cliloride, make the volume up to 200 c.c. 

 and neutralise until there is an acidity equal to 05 per cent, tartaric 

 acid (i.e., until 10 c.c possess an acidity equal to 0"7 c.c. tenth normal 

 acid). Heat, filter, sterilise. 



