PRODUCTS OF METABOLISM 



culture media. Beycrinck gives some instances that result 

 from oxidation by bacterial action: The oxidation of 

 quinic acid to protocatechuic acid is brought about by 

 Micrococcus calco-aceticus andB.fluorescens non-liquefaciens. 

 Quercitol is oxidised to pyrogallol by Pseudomonas aro- 

 matica. Melanine can be formed from tyrosine by Vibrio 

 tyrosinatica, isolated from sea-water and sewage. Aceto- 

 bacter melanogenum, occurring in vinegar, converts peptone 

 into a caramel-like substance. 



Fermentation. By bacteria (Chapter XVIII.); by 

 moulds (Chapter XVI.); by yeasts (Chapter XV.); and by 

 enzymes, or ' zymolysis ' (Chapter XVIII.). 



Putrefaction. Nitrogenous substances, such as the 

 proteins, are decomposed by bacteria, particularly by those 

 of the Proteus group. The insoluble albumins, etc., are 

 first converted into albumoses and peptones; then ammo- 

 acids are produced, and a variety of other substances, such 

 as fatty acids, basic bodies, and gases. 



Indole. Indole is one of the final products of the 

 decomposition of proteins, and is of importance in bacterial 

 diagnosis, as organisms, otherwise very similar, may 

 differ in regard to the production of this substance. To 

 ascertain if an organism produces indole, it is inoculated 

 into peptone water (2 per cent.) or into a glucose-free 

 broth. The culture is incubated for twenty-four hours or 

 longer. Two c.c. of a stock solution of sodium nitrite 

 (5 per cent.) are diluted to 100 c.c. One c.c. of this weak 

 solution is added to the culture (the volume of which 

 should be about 10 c.c.). A little concentrated hydrochloric 

 acid is then allowed to trickle down the wall of the in- 

 clined test-tube to liberate nitrous acid, which gives a 

 pink colour with the indole. If a definite reaction is not 

 obtained, the tube is placed in the blood-heat incubator for 

 half an hour to intensify the colour. At the same time as 

 the peptone water is inoculated, another tube should be 

 infected with an organism known to produce indole, and 

 an uninoculated control- tube placed with the others in the 

 incubator. The purity of the reagents and the power of 

 the peptone to allow production of indole is thus secured. 

 As a more delicate reaction for indole the following reagent 

 may be used: 4 grammes of paradimethylamidobenzalde- 

 hyde are dissolved in 380 c.c. of absolute alcohol and 80 c.c. 

 of concentrated hydrochloric acid. To 2 c.c. of the culture 



