DIFFERENTIATION OF THE BACILLUS TYPHOSUS. 179 



VI. The para-typhoid group of bacilli, which are generally 

 classed as intermediate between B. coli and the B. typhosus, can 

 be distinguished from B. typhosus on account of the power 

 of the para-typhoid group to ferment dextrose. They (the 

 para-typhoid group) are unable, however, to coagulate milk, 

 nor do they produce indol in peptone solutions. This differ- 

 entiates them from the B. coli, which possesses these prop- 

 erties. 



Sources of Pure Cultures. From the spleen of typhoid- 

 fever cases pure cultures of the bacillus may be readily ob- 

 tained in early autopsies and during life; blood extracted' 

 by means of a hypodermatic syringe from this organ will 

 almost always show the bacillus. Indiscriminate punctures 

 of the spleen during life, however, are not to be recom- 

 mended, as this procedure is not free from danger. 



The Bacillus typhbsus has occasionally been obtained from 

 abscesses in the subcutaneous tissue and internal organs in 

 pure cultures in some cases of typhoid fever, showing that 

 this bacillus is at times the cause of suppuration. Cultures 

 may be obtained from the blood of the finger, ear, or, prefera- 

 bly, a superficial vein early in the disease by using the Conradi 

 medium and plating the growth at the end of twenty-four 

 hours. From the faeces, usually after the second week of the 

 disease, and for an indefinite period (in typhoid carriers) the 

 Bacillus typhosus may be recovered. Numerous workers have 

 reported the isolation from the rose spots and some even from 

 the sputum of typhoid-fever cases. 



Artificial Susceptibility. Animals resisting the effects of 

 inoculation with the Bacillus typhosus can be made suscepti- 

 ble by the simultaneous introduction of other saprophytes 

 which seem to overcome their immunity. 



The Blood-Serum Diagnosis of Typhoid Fever. 



The diagnosis of typhoid fever by the blood-serum method 

 is to-day generally employed. As mentioned before, this is 

 based on the principle discovered by Pfeiffer, that the blood of 

 persons suffering with typhoid fever, or who may recently 



