PATHOGENIC BACTERIA. 373 



The crucial test of animal inoculation which furnishes in the 

 case of anthrax, tuberculosis, glanders and other diseases 

 such a sure means of diagnosis cannot be resorted to in the 

 case of typhoid fever for the reason that experiment animals 

 are not subject to spontaneous typhoid and do not take the 

 disease on inoculation with cultures of the typhoid bacillus. 

 It is true that inoculation of animals with the cultures is 

 followed by disease, and the experiments at one time rather 

 encouraged the hope that the results obtained by the inocu- 

 lation of animals with cultures of the typhoid bacillus would 

 furnish a trustworthy means of diagnosis. But the symptoms 

 and lesions produced by the inoculation of typhoid bacilli 

 are so similar to those produced by the inoculation with certain 

 other bacteria that such inoculations cannot be depended 

 upon for differentiation. Some strains of the very bacteria, 

 those of the colon group, which it is important to separate from 

 the typhoid bacillus are so similar to the typhoid in pathogenic 

 properties for experiment animals that a diagnosis between 

 them on this ground is not possible, and it becomes necessary 

 to resort to cultural characteristics and to certain other more 

 or less unsatisfactory tests. 



Of the various media which have been devised, and the 

 various tests which have been recommended the following 

 may be described. 



Loffler introduced a medium consisting of agar-agar 

 colored with malachite green. All bacteria including the 

 typhoid bacillus are retarded in growth upon this medium, 

 and the typhoid bacillus along with certain others change the 

 color of the medium to yellow.* 



The medium suggested by Hissf for the isolation of the typhoid bacillus 

 consists of gelatin and agar, beef -extract, sodium chloride and dextrose, and is 

 given a slightly acid reaction. These substances are used in different propor- 

 tions for plate- and for tube-cultures. This medium is of a semi-solid character, 



*Giinther. Loc. cit. p. 534. 



^Journal Medical Research. Vol. VIII. 1902. 



