APPENDIX 341 



place, the actively motile B, typhosus becomes immotile; and 

 secondly, there is an agglutination, or grouping together in 

 colonies, of the B. typhosus. Neither of these features occurs if 

 healthy human blood is brought into contact with a culture of the 

 typhoid bacillus. There are various ways in which this " serum 

 diagnosis" can be carried out. The simplest and quickest 

 method is as follows: To ten drops of a twenty-four or forty- 

 eight-hours-old neutral broth culture of the typhoid bacillus one 

 drop of the blood serum to be tested is added. The serum and 

 culture are rapidly mixed in the trough of a hollow ground slide 

 (such as is used for the " hanging drop '*), and a single drop is 

 taken, placed upon an ordinary clean slide, and a cover-glass 

 superimposed. The positive reaction of agglutination and im- 

 motility, if the blood comes from a case of typhoid fever, will 

 probably appear within fifteen or twenty minutes. The fluid 

 culture of typhoid may be taken from an agar culture as well as 

 from broth. In both cases it may be desirable to filter through 

 ordinary filter paper to remove any normally agglutinated masses 

 of bacilli before commencing the test. 



In his first experiments Widal used a test-tube in the following 

 manner: The blood to be tested is diluted by one part of it being 

 added to fifteen parts of broth in a test-tube. The mixture is 

 inoculated with a drop of a typical Bacillus typhosus culture. 

 The tube is then incubated at 37° C. for twenty-four hours, after 

 which it is examined. If the reaction be positive, the broth ap- 

 pears comparatively clear, but at the bottom of the test-tube a 

 more or less abundant sediment will be found. This is due to 

 the clumps of bacilli having fallen owing to gravity. If, on the 

 other hand, the reaction is negative, the broth will appear more 

 or less uniformly turbid. 



For the apparatus required to carry out the simpler methods of 

 bacteriological work reference should be made to the standard 

 laboratory text-books, which furnish all necessary details. A 

 good microscope, with a -^ oil immersion lens, is, of course, essen- 

 tial. This can now be obtained for about ;^i 6 (Beck, Swift, Baker, 

 Watson, etc), and the other necessary apparatus is readily obtain- 

 able of Baird andTatlock, Hatton Garden, E.G., and other makers. 



