58 PATHOGENIC BACTERIA 



stances, nevertheless, the result of farther dilutions must be 

 tested, for the reason that the reaction ensues in certain cases in 

 which typhoid does not enter into the question, and, moreover, 

 that the blood of healthy persons possesses at times an unusual 

 degree of the agglutinizing power which is normally present. 



The diagnosis, it may be said, becomes strengthened in pro- 

 portion as the reaction persists on dilution. In certain instances 

 it has been ascertained that a dilution of 1 to 5,000 will yet suf- 

 fice for its production, and even a considerably further dilution 

 than this. The test is to be repeated, therefore, with a dilution 

 of 1 in 20 (i.e., 1 part of serum to 19 of the broth culture), and 

 if still observed, with a dilution of 1 in 50. The last limit may 

 be held to suffice for the exclusion of other possible sources of 

 phenomenon, and to establish a diagnosis of typhoid. The dilu- 

 tion of 1 in 20 is best made by placing nineteen loops of the broth 

 separately on a slide, and mixing with a single loop of the serum; 

 that of 1 in 50, by diluting 1 loop of serum with 10 of distilled 

 water, and mixing one loop of this with four loops of the broth 

 culture. 



After use, all the slides, cover-glasses, and other materials 

 are to be disinfected in a 1 in 20 carbolic acid solution. 



Diphtheria. For the bacteriological investigation of a 

 supposed case of diphtheria it is necessary, firstly, to make a 

 microscopic examination of a culture from the throat or nasal 

 passages ; and secondly, if the investigation is to be complete, 

 to inoculate animals with a pure culture in order to test the de- 

 gree of virulence which the bacillus possesses, i.e., both the 

 morphological and the physiological characters of the microbe 

 should be determined. 



The inoculation of test tubes for the purpose of dia^ nosis 



