STUDIES ON AZOTOBACTER CHROOCOCCUM BEIJ. 333 



relation to the fixation of nitrogen have received considerable 

 attention but it should be stated nevertheless that the ratio 

 C:N, as often reported in the hterature, has no absolute value 

 since the determination of the carbon actually utihzed has 

 not been attempted, a complete consumption of all the carbo- 

 hydrate originally present having been assumed. 



Furthermore it must be stated that by following the practice 

 of allowing all the carbohydrate to disappear from a solution 

 the cultures are submitted to a negative phase, one of actual 

 starvation which, as will be seen later vitiates the results of the 

 experiments. 



The excellent work of Koch and Seydel (1912) on the influence 

 of the concentration of carbohydrate is typical of the results to 

 be obtained when the concentration of sugar and time of incu- 

 bation are made elements in an experiment. In fact from theii* 

 work it is evident that each period of incubation has an optimum 

 concentration of sugar a finding that makes it impossible to draw 

 definite conclusions from data obtained with a given sugar con- 

 centration and an arbitrary number of days of incubation. 



Stoklasa (1908), using glucose as a source of carbon, concludes 

 that the products of carbohydrate attack by Azotobacter are: 

 ethyl alcohol, formic acid, acetic acid, butyric acid (only once in 

 anaerobic conditions), lactic acid, carbon dioxid and hydrogen. 

 From his data it would appear as if the glucose actually incor- 

 porated by the cells during the period of his experiments should 

 be represented by 



grams 



Glucose actually consumed 15 . 8900 



Glucose found in byproducts 9.3790 



Glucose theoretically in cells 6.5110 



But Stoklasa sums up his observations by stating that he can- 

 not account for this quantity of 6.5110 grams of glucose and that 

 probably not all the by-products were determined. A second 

 possible reason for such unaccounted for glucose he assumes to 

 be found in the inaccuracy of the methods for the determination 

 of the by-products (volatile and non-volatile acids). 



