134 ESSENTIALS OF BACTERIOLOGY 



disease, and intense agglutinating serum may be had in severe 

 cases and in cases with relapses. A negative result does not 

 exclude typhoid. 



The test is quantitative i. e., it depends upon the dilution of 

 the blood-serum, since the serum of healthy persons in strong 

 dilution will cause agglutination and loss of motility. 



The test must occur within a certain limit of time to be of 

 value, since agglutination is liable to appear of itself with non- 

 typhoid serums after a period of an hour. 



A serum in a dilution of i : 30 causing complete clumping 

 in half an hour is most likely typhoid. 



The culture must be kept in a vigorous condition by frequent 

 subplanting, and must be tested occasionally with normal 

 serum. Cultures kept in an incubator for a long time tend to 

 adhere in clumps naturally. 



Sedimentation Test. In a test-tube of bacterial emulsion 

 and diluted serum, if the reaction is positive, there will be a 

 flocculent precipitate or sediment at the bottom of the tube, 

 the upper part remaining clear. Compared with normal 

 serum, the cloudiness is diffuse. 



As a clinical test of the disease it has considerable value, 

 although operative at a time when other symptoms have devel- 

 oped sufficiently to determine the diagnosis. 



Staining. Colored with the ordinary anilin dyes, when they, 

 are warmed; since they are easily decolorized, acids should be 

 avoided. 



Gram's method is not applicable. Tissue sections stained as 

 follows: 



Alkaline methylene-blue i hour 



Alcohol 5 seconds 



Anilin-oil 5 minutes 



Turpentine-oil i minute 



Xylol and Canada balsam 



Such a specimen should first be examined with low power, to 

 focus little colored masses, then examined with immersion lens; 

 these masses will be found composed of bacilli. 



