BACILLUS TYPHOSUS 63 



such protected animals is found, when added in 

 small quantity to a broth culture of B. Typhosus, 

 to produce an agglutination of the bacilli ; so that 

 they lose their motility, collect into flocculi visible 

 to the naked eye, and are deposited in a layer at 

 the bottom of the tube, while the supernatant fluid 

 becomes clear. A similar action takes place if the 

 serum of a patient suffering from typhoid fever 

 (except in the first few days of the disease) be 

 added to the culture. This reaction does not take 

 place with serum from other sources (except occa- 

 sionally), nor does this specific serum react thus 

 with cultures of organisms other than the B. 

 Typhosus. Our knowledge of these facts arose 

 from the work of Pfeiffer on Sp. Cholera, was ex- 

 tended by Gruber and Durham, and was applied by 

 Widal to the diagnosis of enteric fever in man. 

 The agglutinating action can be observed under the 

 microscope. Fig. 57 represents the clumping power 

 exerted by serum from a case of typhoid upon the 

 bacillus. Three large masses of agglutinated bacilli 

 are seen in the field, while the rest of the prepara- 

 tion shows scarcely any micro-organisms ; and this 

 clearing of the general field is almost as charac- 

 teristic as the formation of clumps. A red blood 

 cell is seen at the upper part of the field. 



