518 APPLICATION OF METHODS OF BACTERIOLOGY 



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 

 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 agglutinin 

 was present in demonstrable quantities in the circulating 

 blood. 



Experience with both the dry-blood and the fresh serum 

 methods show the culture used to be one of the most impor- 

 tant factors in the test. After deciding upon the most 

 suitable culture for the reaction and it is often necessary 

 to try a great number from various sources it should be 

 transplanted daily into fresh bouillon and kept at a tem- 

 perature 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 a group of cases examined by us by the dry-blood 

 method, including typhoid and other febrile conditions 

 there was a discrepancy between the clinical and the labora- 

 tory diagnosis in from 2 to 3 per cent, of the cases examined. 



In the hands of all who have carefully employed the 



