BACILLUS TYPHOSUS 215 



is very real, and the utmost care in disinfecting all articles used 

 by a patient as well as all excreta cannot be overemphasized. 



Immunity. One attack of typhoid fever usually confers im- 

 munity which lasts for several years ; in about 2 per cent of persons 

 having had one attack a second attack occurs which is usually 

 very mild. Immune serum is highly bactericidal and possesses 

 abundant agglutinins, precipitins, and opsonins. Gradually in- 

 creasing doses of living or dead bacilli injected into animals pro- 

 duces a similar serum, but attempts to use it therapeutically have 

 not met with much success. 



Serum Diagnosis. The fact that the serum of typhoid patients 

 will in high dilutions agglutinate typhoid bacilli, while the serum 

 of normal individuals or those not suffering from the disease has 

 no effect upon them, has been of enormous aid in the diagnosis of 

 typhoid fever. The first application of the test was reported by 

 Widal in 1896. Details of the method have been given in a previous 

 chapter. Usually the reaction is given about the seventh day 

 and gradually increases until convalescence. In about 95 per cent 

 of all cases it is said to appear at some period of the disease. 



Bacterial Diagnosis. A blood culture is generally positive 

 during the first week of the disease in all cases ; during the second 

 week in about 50 per cent of cases, and as the disease progresses 

 the organisms tend to disappear from the blood stream. 



Bacilli seem to be most numerous in the feces during the second, 

 third, and fourth weeks of the disease. The short life of the or- 

 ganisms outside of the body makes it imperative that specimens 

 be examined as soon after passage as possible. 



A small portion of the feces is emulsified if solid in a tube of 

 broth, if fluid it can be plated without further preparation. Poured 

 plates are made of special media such as that of Conradi-Dri- 

 galsky, and a loopful of the fecal material is streaked over the 

 solidified, media. The usual method is to use three plates for 

 each specimen, streaking the second and third plates without 

 recharging the loop. After twenty-four hours' incubation a blue 

 typhoid-like colony is fished into broth and at the end of from 

 eight to ten hours sufficient growth will have developed for the 



