RATE OF GROWTH 



171 



roine and Wurmser * in their work on Aspergillus niger used 

 the dry-weight method which they considered in relation to 

 the amount of organic matter used up in growth ; the ratio 

 of the dry weight of the organism to the organic matter con- 

 sumed, giving the coefficient of utilization. For Aspergillus 

 grown in a culture medium of salts together with 3 per cent, 

 glucose, the sole source of carbon, and 0-05 per cent, ammonium 

 sulphate, the only source of nitrogen, the coefficient of utiliza- 

 tion was found to be 0-44. This value is unaltered when 



b 



-o 



o 



c 



18 



16 



14 



12 



10 



8 



6 



4 - 



2 - 



Dec. Jan. Feb. Mcb. Apr. May 



Fig. 7. 



June 



glucose is replaced by other sugars and when the concentration 

 of the ammonium sulphate is much increased or is replaced 

 by guanidine, urea or nitric acid ; nitrates, on the other 

 hand, bring about a reduction in the coefficient. For the 

 production of I gram of mycelium in ordinary conditions of 

 growth, 2-3 grams of glucose are used ; 2-2 grams are required 

 for actual growth, the rest being consumed in respiratory 

 processes. 



The rate of growth of Aspergillus niger is influenced by the 

 hydrogen ion concentration of the culture medium ; a range 



*Terroine and Wurmser : " Bull. Soc. Chim. Biol.," 1922, 4, 519. 



