PATHOGENIC BACTERIA. 303 



plain agar i per cent, of a saturated aqueous solution of neutral 

 red, some also add 0.3 per cent, dextrose. 



In Dunham's peptone solution indol is ruot formed, as a 

 rule. On potato it usually forms what is called an invisible 

 growth; that is, although no development is apparent to the 

 eye, numerous bacilh may be shown under the microscope 

 in smear preparations made from the surface of potato inocu- 

 lated about forty-eight hours previously. Occasionally a 

 slight visible growth is seen on potato. 



The typhoid bacillus is killed at 60° C. in ten minutes. It 

 resists drying well. It can survive in soil and sewage a long 

 time. 



For a comparison of the properties of the typhoid bacillus 

 and the colon bacillus see the latter. 



A new medium has been suggested by Hiss* for the isolation of the typhoid 

 bacillus. It consists of gelatin and agar, beef-extract, sodium chloride and 

 dextrose, and is given a slightly acid reaction. These substances are used in 

 different proportions for plate- and for tube-cultures. This medium is of a 

 semi-solid character, and the great motility of the typhoid bacillus in produc- 

 ing a uniform clouding of the medium in tubes, with the absence of a gas-forma- 

 tion, is made use of to distinguish this organism from the colon bacillus; in 

 plate-cultures the colonies exhibit peculiar filamentous outgrowths. It is 

 claimed that it can be determined whether organisms are typhoid baciUi or 

 not after thirty-six hours in the incubator by this method. 



Other special media for the identification of the typhoid bacillus have been 

 devised by Eisner, Stoddart, by Capaldi and Proskauer, and by Piorkowski.f 

 The medium of Stoddart is based upon principles similar to those appUed in 

 the medium of Hiss. 



The Drigalsky-Conradi J method for isolating the B. typhosus from water 

 and feces is that now most employed. The principle of this method consists 

 in the use of a culture-medium on which the surface colonies of B. coli and of 



* Journal Medical Research. Vol. VIII. 1902. 



t Eisner. Zeitschrijt jiir Hygiene. Bd. XXI., p. 25. 1895. Stoddart. 

 Journal oj Pathology and Bacteriology. Vol. IV., p. 429. 1897. Capaldi and 

 Proskauer. Zeitschrijt jiir Hygiene, etc. Bd. XXIII., p. 452. 1896. Pior- 

 kowski. Berliner klinische Wochenschrijt. P. 145. 1899. 



% Drigalsky-Conradi. Ueber ein Verfahren zum Nachweis der Typhus- 

 bacillen. Zeitschrijt jiir Hygiene und Injectionskrankheiten. Bd. XXXIX. 

 1902. 



