328 TYPHOID FEVER 



fluorescence. Fitz- Gerald and Dreyer have shown that an 

 important factor here is the reaction of the medium, and that the 

 effects of the bacteria may be one of degree, under certain 

 circumstances the effects described as characteristic of the two 

 organisms may be reversed. 



(3) Formation of IndoL Among the bacteria capable of 

 forming indol is to be classed the b. coli. Indol can be 

 recognised in bouillon cultures of the b. coli three to four days 

 old by the usual tests (vide p. 77). As there is no evidence 

 that it can produce nitrites a small quantity of the latter must 

 be added. The typhoid bacillus never gives this reaction when 

 growing in ordinary conditions, but on the other hand, it 

 appears that some varieties of the b. coli fail to produce it also. 

 Peckham, however, has found that if the typhoid bacillus be 

 grown in peptone solution, after a few generations of three 

 days each it may acquire the property of producing indol. The 

 formation of indol by an organism after the first transference to 

 peptone solution from one of the ordinary media may, however, 

 be accepted as evidence in favour of the organism not being the 

 typhoid bacillus. It is to be noted here that the presence of 

 sugar in a medium retards the production of indol by the b. 

 coli. The indol reaction thus ought to be sought for in a sugar- 

 free medium. 



(4) The Media of Capaldi and Proskauer. The first of these 

 ("No. 1 ") is a medium free of albumin, in which b. coli grows 

 well and freely produces acid, while the typhoid bacillus hardly 

 grows at all, and certainly will produce no change in the 

 reaction. Its composition is as follows : asparagin '2 parts, 

 mannite *2, sodium chloride "02, magnesium sulphate '01, 

 calcium chloride '02, potassium monophosphate '2, distilled 

 water to 100 parts. The second medium ("No. 2") contains 

 albumin, and is such that the b. coli produces no acid, while 

 the typhoid bacillus grows well and produces an acid reaction. 

 It consists of Witte's peptone 2 parts, mannite *1, distilled water 

 to 100 parts. After the constituents of each medium are mixed 

 and dissolved, it is steamed for one and a half hours and then 

 made neutral to litmus the first medium, being usually naturally 

 acid, by sodium hydrate, the second, being usually alkaline, by 

 citric acid. The medium is then filtered, filled into tubes con- 

 taining 5 c.c., and these are sterilised. After inoculation for 

 twenty hours the reaction of the medium is tested by adding 

 litmus. 



(5) The Application of the Agglutination Test in distinguish- 

 ing B. typhosus from B. coli. The scope of the application of 



