CHAPTER XXV 



DIAGNOSIS OF TYPHOID FEVER AND FOOD-POISONING INFECTIONS 



The Widal Test. To carry out this test one must have a 24-hour-old cul- 

 ture of the typhoid bacillus free from clumps. To determine the presence or 

 absence of clumps a loopful of the culture is placed on a cover glass, the cover in- 

 verted and placed on a hanging-drop slide so that the fluid is suspended in the 

 well. The preparation is examined under the microscope and if numerous, 

 isolated, actively motile bacilli are observed the culture is fit for use; if bacilli are 

 few or not motile another culture must be procured, and if clumps of bacteria are 

 observed they must be removed before it is fit for agglutination tests. Clumps 

 are removed by filtration through sterile filter-paper. 



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FIG. 23. WIDAL REACTION. 



Upper half of field shows a negative reaction, no agglutination. Lower half of field shows a 

 positive reaction, agglutination of bacilli. (12 X eyepiece and M2 oil immersion objective.) 



The ear or finger of the patient is cleaned and pricked with a needle or lancet. 

 Several drops to i cc. of blood are collected in a sterile capillary tube, a Wright's 

 capsule or upon a clean glass slide. If collected in a tube or capsule the ends 

 are plugged with cotton or otherwise sealed. The blood coagulates in the tube 

 and clear serum separates. When the test is performed the serum alone is used. 



If collected on a slide the blood is allowed to dry and when the test is per- 

 formed several drops of sterile water are mixed with the dried blood and the 

 liquefied whole blood is used. 



Having obtained the blood or blood serum and the culture, a hanging-drop 

 slide and several cover glasses are cleaned. 



