140 ESSENTIALS OF BACTERIOLOGY 



tective. Bacterins are made from a weakly virulent culture. 

 The results so far obtained would indicate that this inocula- 

 tion has some value, but the evidence is far from conclusive 

 and the statistics on the subject require more careful study 

 before they can be accepted as positive proof. An eighteen- 

 hour agar surface growth is washed in sterile salt solution 

 and killed by heating at 56 C. one hour. It is then diluted 

 so as to contain one billion bacilli to i c.c. Tricresol, 0.25 per 

 cent., is added to preserve, and animals tested for purity of the 

 vaccine. A slight local reaction follows the inoculation; 

 about three injections of jE/2, i, and one billion bacilli at ten- 

 day intervals, render the subject immune. General symp- 

 toms rarely occur. 



The Gruber-Widal Blood-serum Test. In 1896 Widal and 

 Griinbaum, working separately, developed what is now spoken 

 of as the "Widal serum test," or "Widal reaction," or aggluti- 

 nation test. 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 

 microscope. Within fifteen minutes to an hour the motility 

 of the bacilli will cease, and they will have arranged them- 

 selves into clusters, as if stuck or glued together (Fig. 61). 

 If this reaction occurs within an hour, and with the proper 

 dilution of the serum, the patient has or has had typhoid 

 fever. Widal first used the serum of the blood; this has 

 been modified so that a drop of dried blood is sufficient. 



Method of Test. 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 i : 5. One 

 drop of this is then mixed with one drop of a bouillon culture 

 of typhoid bacilli of about twenty-four-hours' growth, and 

 examined under the microscope in the hanging drop. Weaker 



