162 TYPHOID FEVER. 



The Bacillus typhosus 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. 



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 

 have had the disease, when mixed with young cultures of 

 Eberth's bacillus, has the property of arresting the active 

 motion of the bacilli, and causing their agglutination or 

 clumping. This power resides in the serum, and is due to a 

 substance called agglutinin. 



Widal inaugurated the blood-test for typhoid fever, and sug- 

 gests that to 1 c.c. of bouillon culture, not more than twenty- 

 four hours old, and grown at a temperature of 35 C., 0.10 c.c. 

 of the serum to be tested be added. The serum may be 

 obtained either by allowing the drawn blood to coagulate, or 

 by means of a small blister. In the space of from five to 

 ten minutes all motion of the bacilli is arrested, and these 

 come together, forming peculiar clumps. This clumping may 

 be seen both in the hanging drop, and even by the naked eye 

 in culture-tubes. Ordinarily the hanging-drop method is 

 adopted, as it requires much less serum, and is therefore less 

 injurious and vexatious to the patient. 



Wyatt Johnston's Dried Blood Method. This observer has 

 demonstrated that the same reaction may be obtained by the 

 use of dried blood instead of fresh serum, and that even after 

 the blood has been dried for several days or weeks it still 

 retains its agglutinating power. The procedure in detail is as 

 follows : 



