65 



selves and of the appearance of the growth in the different 

 cultures of B. coli communis and the bacilli of hog cholera 

 and typhoid fever. 



The cultures, excepting those in milk, can be rejected 

 now or, if desired, they may be kept for further study and 

 comparison. 



EXERCISE XXXIV. 



WIDAL SERUM TEST. 



1 06. Explanatory note. This test depends upon the 

 fact that when the blood serum of a person suffering with 

 typhoid fever or who has recently recovered from it is added 

 to a bouillon culture of the bacillus, the bacilli become less 

 motile and soon agglutinate in small clumps. The dilutions 

 used vary from equal parts of serum and culture to dilutions 

 of i to 50,000. It is recommended that weaker dilutions 

 shall be used, i. e., from 1:10 to 1:50. The test is believed 

 by many to be possessed of much diagnostic value. It was 

 observed by Dr. C. F. Dawson to apply to hog-cholera 

 bacilli. (New York Medical Journal, Feb. 20, 1897.) 



107. General directions. Take 2 loopfuls of a fresh 

 bouillon culture of typhoid bacilli (which will be furnished) 

 and place them on a cover-glass, add one loopful of blood 

 serum from a typhoid patient or the blood of an immune guinea 

 pig and immediately make and examine a hanging-drop prep- 

 aration with a loopful of the mixture. Note the effect on the 

 motility and the aggregation into clumps. Specify the time 

 elapsing before the agglutination is well marked. 



Make a similar examination of a culture to which i/io 

 blood serum has been added. 



Repeat the above test with the blood from animals affected 

 with or immunized against hog cholera. 



