664 PATHOGENIC MICROORGANISMS 



he recommended, for the diagnosis of the disease, the employment of a 

 microscopic agglutination test carried out by the usual hanging-drop 

 technique. The reaction of Widal is, at present, widely depended upon 

 for diagnostic purposes and although not universally successful, owing 

 to irregularities in agglutinin formation in some patients and because of 

 differences in agglutinability of the cultures employed, it is nevertheless 

 of much* value. The fact that the recent work of Hooker and of Weiss 

 has shown that typhoid bacilli differ in antigenic properties, and may 

 on the basis of agglutination and agglutinin absorption be divided into a 

 number of groups, is not of sufficient practical importance to necessitate 

 the use of a variety of strains since the atypical antigenic ones are rela- 

 tively rare. Original conclusions as to the dilutions of the serum which 

 must be employed, have, however, necessarily been modified. Owing 

 to the fact that Gruber, 65 Stern, 66 Frankel, 67 and a number of others 

 have found that occasionally normal serum will give rise to agglutina- 

 tion of typhoid bacilli in dilutions exceeding 1 : 10, it has been found 

 necessary, whenever making a diagnostic test, to make several dilutions, 

 the ones most commonly employed being 1 : 20, 1 : 40, 1 : 60, and 

 1 : 80. The wide application of the method has given rise to the 

 development of a number of technical procedures, all of them devised 

 with a view toward simplification. In ordinary hospital work, it is 

 most convenient to keep on hand upon slant agar, a stock typhoid 

 culture, the agglutinability of which is well known. From this stock 

 culture, fresh inoculations upon neutral bouillon should be made each 

 day, so that a young broth culture may always be on hand to furnish 

 actively motile, evenly distributed bacteria. These bouillon cultures 

 may be grown for from six to eight hours at incubator temperature or 

 for from twelve to eighteen hours at room temperature. The tempera- 

 tures at which the broth cultures are kept .must depend, to a certain 

 extent, upon the peculiarities of the typhoid bacillus employed, since 

 some strains are more actively motile and furnish a more suitable 

 emulsion if kept at a temperature lower than 37.5 C. A false clumping 

 in the broth cultures due to a too-high acidity of the bouillon or a too- 

 prolonged incubation must be carefully guarded against. It is also 

 possible to use for this test an emulsion of typhoid bacilli prepared by 

 rubbing up a small quantity of a young agar culture in salt solution. 

 Uniformity in the preparation of broth cultures or of emulsions should be 

 observed, since the quantitative relationship between typhoid bacilli 



65 Gruber, Verhand. Congr. f. inn. Med., Wiesbaden, 1896. 



66 Stern, Cent. f. inn. Med., xlix, 1896. 



67 Frankel, Deut. med. Woch., ii, 1897. 



