A manual of bacteriology, clinical and applied / by R. Tanner Hewlett.

  • Hewlett, R. Tanner (Richard Tanner), 1865-1940.
Date:
1914
Catalogue details

Licence: In copyright

Credit: A manual of bacteriology, clinical and applied / by R. Tanner Hewlett. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

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    INDOLE then leucin, tyi'osin, and glycocol, and basic compounds to which the name of ptomine has been given ; next indole, skatole, and phenol, and volatile fatty acids ; and lastly, mercaptans, sulphuretted hydrogen, marsh gas, aramonia, carbonic acid, and hydrogen. In view of its practical importance in bacteriological analysis and the identification of species, indole may here be referred to at some length. Indole—Indole (C8H7N) is a product of the putrefactive decomposition of proteins containing a tryptophane nucleus and is formed during the growth of many organisms, and, since one species may produce it and another alHed one may not, the determination of its presence or absence in the culture may be of value in the identification of organisms. The detection of indole is based on the reaction with nitrous acid, with which it gives a fine purphsh-red coloration. In order to test for it, the organism is grown in a fluid medium for twenty-four to forty-eight hours or longer, 1 c.c. of a 0*1 per cent, solution of sodium nitrite is added to every 10 c.c. of the culture, and a few drops of pure concentrated sulphuric acid or of hydrochloric acid are allowed to trickle slowly down the side of the test-tube, which is inclined with its mouth away from the operator. As the acid runs down, it is mixed with the fluid ; a colour varying from pale pink to pale purple indicates the presence of indole. A control tube, iminoculated, should also be similarly tested to make sure that the reaction is due to the products of the growth of the organism. The culture fluid usually employed is peptone water, preferably 2 per cent., but some samples of peptone occasionally fail to give the indole reaction when organisms are grown in media prepared fi'om them ; the right kind of peptone must, therefore, be used. As the dilute solution of sodium nitrite is unstable, a stock 5 per cent, solution may be kept; 2 c.c. of this solution