BACILLUS TYPHOSUS 491 



which all the available clinical evidence is opposed to either 

 the positive or negative results of the test, the difficulty is 

 much more certainly cleared away by the use of highly dilute 

 and exactly diluted fresh serum than by this method. Com- 

 petent 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 

 pecuharities, 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 agglutinin 

 was present in demonstrable quantities in the circulating 

 blood. 



Experience with both the dry-blood and the fresh s^um 

 methods at the Municipal Laboratory of Philadelphia 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 f^-ctors in the test. After deciding upon the 

 most suitable culture for the reaction — and it is often neces- 

 sary to try a great number from various sources — we have 

 adopted the plan of daily transplanting the culture into 

 fresh bouillon and keeping it at a temperature rarely above 

 20° or 22° C. The bacilli grown under these circumstances 

 are usually somewhat longer than when cultivated at higher 

 temperature, and they exhibit a regular, gliding motility 

 that renders it more easy to follow the individual cells 

 under the microscope than when they possess the usual 

 active, darting motion. 



In the group of cases examined by us by the dry-blood 

 method, including typhoid and other febrile conditions 



