424 BACTERIOLOGY. 



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 : 15 to 1 : 20, as 

 determined by the ha3moglobinometer. 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 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 examination was 

 not made at a time when agglutiuin was present in de- 

 monstrable quantities in the circulating blood. 



Experience with both the dry-blood and the fresh 

 serum methods at the Municipal Laboratory of Phila- 

 delphia in more than 12,000 examinations from about 

 10,000 febrile conditions, lead us to regard the culture 

 used as one of the most important factors in the test. 

 After deciding upon the most suitable culture for the 



