27 



Incubation at 30 degrees C. for three to five days is recommended. 

 This synthetic medium may also be used for the Voges Proskauer test by 

 mixing with it (at the time of addition of the alkali) 0.1 percent pure 

 casein. 



Evidence from Nitrogen Metabolism. In the foregoing paragraphs 

 it was pointed out that there were two main divisions in the colon group 

 which could be easily distinguished by differences in carbohydrate meta- 

 bolism. It is becoming apparent that the differentiation may also be 

 made upon nitrogen metabolism. 



In 1903, Rettger noted that the products of protein metabolism (mer- 

 captan, scatol, phenols aromatic axyacids, etc.) are formed much more 

 slowly by Bact. aerogenes than by Bact. coli. 



Koser (1918) in a study of 124 colon cultures found that in a medium 

 containing uric acid as the sole source of nitrogen the V. P.-)- strains 

 (aerogenes section) grew luxuriantly whereas the V. P. strains (coli 

 section) failed to grow. 



TABLE XII. DIFFERENTIATION OF COLI AND AEROGENES SECTIONS 



(After Koser, 1918) 



5 grams. 

 0.2 grams. 

 0.1 grams. 

 1.0 grams. 

 30.0 grams. 

 0.5 grams. 



The medium employed by Koser consisted of the following: 

 Distilled ammonia free water 1000 c. c. 

 NaCl 



Magnesium sulphate 

 CaCl 2 



Dipotassium phosphate 

 Clycerol 

 Uric acid 



Sterilization is in the autoclave at 13 to 15 pounds for 15 minutes. 

 A slight turbidity, presumably due to the finely divided precipitate of cal- 

 cium sulphate may be evident immediately after autoclaving but disap- 

 pears on cooling. 



A solid uric acid medium may be prepared by the addition of 1.5 

 percent washed agar. 



He suggests the differentiation is due to the inability of the strains in 

 the Coli Section to break down the purin ring and thus obtain nitrogen 

 for growth from the uric acid. 



NHC '-O 



I I 



o~c c 



I 



NH 



* 

 CNH/ 



