118 ESSENTIALS OP BACTERIOLOGY. 



into the peritoneum of guinea-pigs, prevented infection from 

 taking place, and the spirilla were transformed into granular 

 masses. He likewise showed this reaction to be specific, the 

 serum of cholera-immune animals acting only on cholera 

 vibrio; and hence he suggested using the serum as a means 

 of diagnosis for the cholera vibrio and typhoid bacillus. Gru- 

 ber about the same time made some studies upon the use of 

 this serum property in differentiating bacteria, but it was con- 

 sidered as yet a property connected in some way with immu- 

 nity. 



In 1896, Widal and Griinbaum, working separately, developed 

 what is now spoken of as the "Widal serum-test," or "Widal 

 reaction." It consists in testing a drop of blood of a patient 

 suspected of having typhoid fever, by mixing a dilution of it 

 with a drop of a fresh bouillon culture of typhoid bacilli, and 

 examining the mixture in a hanging drop under the micro- 

 scope. Within fifteen minutes to an hour the motility of the 

 bacilli will cease, and they will have arranged themselves into 

 clusters, as if stuck or glued together. If this reaction occurs 

 within an hour, and with the proper dilution of 'the serum, the 

 case is one of typhoid. Widal first used the serum of the blood ; 

 this has been modified so that even a drop of dried blood is suf- 

 ficient. The method as applied in city laboratories is as follows : 

 The physician is told to clean the finger of the patient with 

 water (no germicides), and with a needle draw a drop of blood 

 on to a piece of ordinary note-paper. This is then sent to the 

 laboratory ; the paper with the dried blood is soaked for a few 

 minutes in a watch-glass containing 4 drops of clean water, thus 

 obtaining a dilution of 1 : 5. One drop of this is then mixed with 

 one drop of a bouillon culture of typhoid bacilli of about 24 

 hours' growth, and examined under the microscope in the 

 hanging drop. Weaker dilutions of the serum have been rec- 

 ommended (1 : 50), and this should be used in cases of doubt 

 So far, about 95 per cent, of the cases examined, and which clin 

 ically were considered typhoid fever, have given a positive reac- 

 tion. It is not often present until the fifth day of the fever, and 

 disappears usually within a year, though in some individuals it 

 has been found ten years after an attack of the disease. 



