BACILLUS TYPHOSUS. 425 



good for diagnostic purposes from the dried blood as 

 from the serum. 



The Typhoid Culture Employed. It is important that 

 the culture employed for serum-tests should be a suit- 

 able one, for although in our experience all cultures 

 show the reaction, yet some respond much better than 

 others. A broth culture of the typhoid bacillus de- 

 veloped at 35 C., not over twenty-four hours old, in 

 which the bacilli are isolated and actively motile, has 

 been found to give us the most satisfactory results. 

 Stock cultures of typhoid bacilli can be preserved on 

 nutrient agar in sealed tubes and kept in the ice-box. 

 These remain alive for months or even years. From 

 time to time one of these is taken out and used to 

 start a fresh series of bouillon cultures. 



The Dilution of the Blood-serum to be Employed and 

 the Time Required for the Development of Reaction. The 

 serum test, as has been pointed out, is quantitative and 

 not qualitative. By this it is not meant to assert that the 

 agglutinating and immobilizing substances produced in 

 the blood of a patient suffering from typhoid infection 

 are the same as those present at times in normal blood, 

 or those produced in the blood of persons sick from 

 other infections. It is intended, however, to maintain 

 that the effect upon the bacilli, as seen under the micro- 

 scope, is identical, the difference being that in typhoid 

 fever, as a rule, substances which cause this reaction 

 are usually far in excess of the amount which ever 

 appears in non typhoid blood, so that the reaction 

 occurs after the addition to the culture of far smaller 

 quantities of serum than in other diseases, or when the 

 same dilution is used it occurs far more quickly and 

 completely with the typhoid serum. 



