124 THE ACUTE SELF-LIMITED INFECTIONS 



observed under the microscope after they have stood 

 together for a definite time, and the presence of clump- 

 ing, with loss of movement, noted. In case this occurs 

 typhoid is present. This agglutination reaction is 

 called the Widal test, and is positive in about 95 per 

 cent, of all cases (see Figs. 33 and 34.) 



Cultures. It is also of aid in the diagnosis of typhoid 

 to make a blood culture. This consists in withdrawal, 

 under sterile conditions, of blood from a vein, placing 



Fi(r. 36. Typhoid bacilli from nutrient gelatin. X 1100 diameters. 

 (Park.) 



it into suitable culture medium, and keeping it at body 

 heat in the incubator. If typhoid bacilli be present 

 they will grow so that we may isolate and identify 

 them. The bacilli may be isolated also from the 

 feces and urine during an attack, and as mentioned 

 above, for a long time afterward in the case of carriers. 

 The methods for isolation are tedious and difficult, 

 and need not be described here. Many technics have 

 been devised to hasten work on epidemics and carriers, 

 but none is as yet very good. 



