212 INFECTION AND IMMUNITY. 



phagocytes; if phagocytosis is inhibited by some 

 means the agglutinated organisms are found to be 

 still virulent. 



Koch has attempted to use the agglutination 

 test with the tubercle bacillus as an index of im- 

 munity against tuberculosis. This is not accepted 

 as a reliable test for the immunity, but is perhaps 

 a general index of the ability of the individual to 

 form antibodies for this organism. This method 

 was devised inasmuch as the bactericidal action of 

 a serum on the tubercle bacillus is not readily de- 

 termined. 

 Technic of One may use two methods of determining the 



the Agrgluti- , ,. ' r , . 



nation Test, agglutination of bacteria: 1. the macroscopic or 

 naked eye observation of the clumping and sedi- 

 mentation of a homogeneous suspension of the 

 bacteria in test-tubes; 2, the microscopic observa- 

 tion of the clumping of the organisms when the 

 latter are mixed with serum and mounted as a 

 "hanging-drop" preparation. 2 



The Bacterial When the organism to be tested grows rapidly, 

 it is the custom to use a young culture, one which 

 has grown on an agar surface or in bouillon for 

 from eighteen to twenty-four hours. Older cul- 

 tures of the typhoid bacillus or of the cholera 

 vibrio are agglutinated with more difficulty than a 

 young culture. If an agar culture is used, the 

 bacteria may be washed from the surface by pour- 



2. For a hanging-drop preparation it is necessary to have 

 a slide with a saucer-shaped depression on one surface. A 

 drop of the solution to be examined is mounted on a cover 

 glass, and the latter is then mounted, drop side down, over 

 the depression and the edges of the cover-glass sealed with 

 vaselin or paraffin. There is ample room for motile organ- 

 isms to swim about in such a preparation, and the loss of 

 motillty incident to agglutination is readily observed. 



