COMMON COMMUNICABLE DISEASES. 



Widal's Test is based upon the fact that the "Widal's 



Test " 

 blood serum of a person who has typhoid fever 



is antagonistic to the bacillus typhosus. A 



drop of blood is obtained from the suspected 



patient by pricking the lobe of his ear. This 



drop is placed on a clean glass slide and covered 



with another slide immediately to prevent other 



germs which may be lurking about from getting 



into it, and it is then allowed to dry. A little of 



the bouillon, or other substance, in which the 



bacillus typhosus is being cultivated is then 



placed on another clean glass slide and covered. 



The dried blood of the suspected patient is made 



into a watery solution and added to the culture. 



From this mixture of dried blood and typhoid 



bacillus, what is known as a "hanging drop" 



preparation is made under the microscope. 



If the patient has typhoid fever the bacilli will 



be seen rapidly to lose their power of motion 



and to form into tangled clumps, or masses, 



and so get away from the blood serum of the 



patient. If typhoid fever does not exist, this 



clumping and entanglement of the bacilli and 



arrest of their movements does not occur. 



There is said to be an exception to this rule in Exception to 



cases where the patient has had the disease *Widal's Test. 



* German authorities spell this scientist's name Vidal, 

 and assert that he is French and that the American 

 spelling, "Widal," has arisen because of the German 

 pronunciation of the letter V. The French alphabet does 

 not contain the letter W. 



79 



