CHAPTEE XXIII. 



THE ISOLATION OF THE-TYPHOID AND COLON BACILLI 

 FROM WATER, STOOLS, ETC. AND THE METHODS 

 OF IDENTIFYING THE TWO ORGANISMS. 



Introduction. 



Section I. The isolation of the typhoid and colon bacilli, p. 402. 



1. Original methods, p. 402. 2. Eisner's method and its modifications, p. 403. 

 3. Precipitation methods, p. 406. 4. Method based upon the motility of the typhoid 

 bacillus, p. 406. 5. Chantemesse's carbolic media, p. 407. 6. Conradi-Drigalski's 

 method, p. 407. 7. Endo's medium, p. 408. 8. Caffeine media, p. 408. 9. Malachite 

 green media, p. 409. 10. China green medium, p. 410. 11. Bile media, p. 410. 12. 

 Brilliant green medium, p. 411. 13. Neutral red media, p. 411. 14. Methods based 

 upon agglutination, p. 412. 15. MacConkey's media, p. 412. 



Section II. The identification of the typhoid and colon bacilli, p. 412. 



THE isolation of the typhoid bacillus from water, etc. in which it is mixed 

 with other species of organisms, and especially when the colon bacillus is 

 also present, presents certain difficulties which may be summed up under 

 four headings. 



1. On gelatin media, at the ordinary temperature of the atmosphere, 

 colonies of the typhoid bacillus develop slowly (requiring about 48 hours) 

 while saprophytic organisms which liquefy the medium grow more quickly 

 and so put an end to the investigation. 



2. The colon bacillus very often retards the growth of the typhoid bacillus 

 when the two organisms are sown together on artificial culture media, with 

 the result that the presence of the latter may pass unnoticed. There is, in 

 fact, a true antagonism between the colon bacillus and the typhoid bacillus 

 (Grimbert). A similar antagonism also exists between certain other micro- 

 organic species and the typhoid bacillus when sown together on artificial 

 media (Besson). 



3. Remy, though he does not admit that the typhoid bacillus is crowded 

 out by the colon bacillus, nevertheless lays stress on the difficulty of isolating 

 the former when the latter organism is also present. He shows that by 

 growing the two organisms together their properties may be profoundly 

 modified : thus the typhoid bacillus occasionally loses its property of being 

 agglutinated by a specific serum, and the colon bacillus may under like con- 

 ditions lose its indol-producing and fermentation properties. 



4. The ordinary method of gelatin-plating only permits of a very small 

 quantity of a suspected water being sown and it is therefore possible that if 

 the typhoid bacillus be present only in small numbers as compared with other 

 organisms, it may escape notice. 



2c 



