438 BACTERIOLOG Y. 



is gently rubbed upon the drop of dried blood until tin- 

 contents of the loop are of a dark amber color; this is 

 then mixed with a drop of a bouillon culture of typhoid 

 bacilli on a cover-glass, which is mounted upon the 

 hollow-ground slide as a hanging drop, when the effect 

 of the diluted blood upon the culture can be observed 

 with the microscope. The reaction, if positive, should 

 occur within a half hour. Many object to this method 

 because it is impossible accurately to dilute the blood 

 by the plan used. A number of tests have shown us 

 that preparations made in this way correspond roughly 

 with a fresh-blood dilution of from 1 : 1 o to 1 : 20, as 

 determined by the haemoglobinometer. In a small 

 number of cases in which parallel tests were made 

 with this and with fresh fluid serum the results were 

 concordant. We are inclined to the opinion, however, 

 that in doubtful cases, in which all the available clin- 

 ical evidence is opposed to either the positive or nega- 

 tive results of the test, the difficulty is much more 

 certainly cleared away by the use of highly diluted 

 and exactly diluted fresh serum than by this method. 

 Competent observers are of the opinion that in all 

 such cases the quantity of serum in the hanging drop 

 should be decreased until it is present in the proportion 

 of from (not less than) 1 : 50 to 1 : 60, and that, if after 

 exposure to this dilution for two hours the bacilli are 

 still motile and not clumped together, or the reaction is 

 deficient in only one or the other of these peculiarities, 

 the case from which the serum was obtained may be safely 

 regarded as not typhoid fever, or if typhoid the exami- 

 nation was not made at a time when agglutinin was pres- 

 ent in demonstrable quantities in the circulating blood. 

 Experience with the dry-blood method at the Mu- 



