356 TYPHOID FEVER 



The bulb is then filled with 2 per cent, sodium hydrate solution, the 

 opening closed with the thumb and thoroughly shaken. After the gas 

 has been collected in the closed arm the thumb is removed and the ratio 

 of the hydrogen left to the original gas volume is read off. 



Voyes and Proskauer'.t Reaction. — This is a reaction which is 

 not given by the classical type of b. coli, but as it occurs with 

 many members of the coli group it may be described here. It 

 also depends on carbo-hydrate fermentation. A glucose peptone 

 solution tube is inoculated and incubated for three days. A 

 solution of caustic potash is added and the tube allowed to stand 

 for twenty-four hours at room temperature. A red fluorescent 

 colour is produced, causing the medium to resemble a weak 

 alcoholic solution of eosin. 



B. Action on Neutral-Red. — Wher^b. coli is grown on neutral- 

 red lactose bouillon, a rosy red colour, the effect of the lactic 

 acid upon the dye, is at first seen. Frequently this is succeeded 

 by the appearance of a green fluorescence due to a direct action 

 of the organism upon the dye. This is evidenced by the fact 

 that the neutralisation of the lactic acid by an alkali does not 

 lead to a reproduction of the original alkaline tint in the in- 

 dicator. The degree of change, however, varies with composition 

 of the medium, the important factors being the percentage of 

 sugar, the reaction, and the strain of the bacillus used. 



C. Production of Indol. — The b. coli produces indol in pep- 

 tone water. The methods have been given on page 81, and 

 for the detection of the reaction the use of Ehrlieh s rosindol 

 test is preferable (if the nitroso-indol test be used, a small 

 quantity of a nitrite must be added). Two peptone tubes should 

 always be inoculated, and if the reaction is not obtainable in 

 one after two or three days' growth, the other should be incubated 

 for from six to seven days and then tested. Where a faint 

 reaction is obtained, it is well to corroborate the presence of indol 

 by dissolving the rosindol out with amyl-alcohol as described. 



D. Reduction of Nitrates. — The b. coli is frequently capable 

 of reducing nitrates to nitrites. For this test, Savage recom- 

 mends the use of a medium made by dissolving 10 grms. of 

 peptone in 1 litre of ammonia-free distilled water, and adding 

 2 grms. of nitrite-free potassium nitrate. The medium is filtered, 

 tubed, and sterilised for half an hour on three days. Tubes 

 are infected and incubated for forty-eight hours, the forma- 

 tion of nitrites being now tested for by Ilosvay's method. 

 The following solutions are required : (a) sulphanilic acid, "5 

 grm. dissolved in 150 c.c. dilute acetic acid (s.g. 1"04); (b) 

 1 grm. a-naphthylamine is dissolved in 22 c.c. of water, the 



