IM PORTA XCE OF AXTIBODIKS IX DIAGNOSIS 



381 



suspension has been determined by sera of known potency, the posi- 

 tive human serum control is omitted. 



Incubation, Observation and Interpretation of Results. — 

 The tubes are shaken and inculcated at 50° C. to 55° C. for two 

 hours and then observed. These conditions favor the demonstration 

 of H agglutinins. To demonstrate agglutinins the incubation 

 should be continued for 24 hours. The first tube containing normal 

 serum mixed with bacteria should show uniform turbidity, while 

 in the second containing known positive serum and suspension, one 

 should see a complete or partial agglutination and settling out of 



V 



-n^-p 



\^ 



y^ 



Tote 

 Serom ■ 



rfesoit. - 



V 



J. i 5 'V 



norma\ tosit'ive R>t>eriis SaVine 

 donirol 



Negative 

 Wiial Rea.c-t.on 



Fig-. 16.— Negative W^iclal test. 



clumps. Tlie patient's serum is in tube three and this tube is to 

 be compared with tubes one and two. If it is negative, it will be 

 like the former, while if it is positive it will be like the latter. The 

 saline control, tube four, should show uniform turbidity. Figs. 15 

 and 16 show positive and negative Widals, respectively. 



Microscopic Method. — The microscopic method has inherent in 

 it several sources of error to which exceptions are taken, but it does 

 give some information not discoverable Ij.y the macroscopic test. 

 In carrying out the microscopic technique, one prepares reagents 

 as for the macroscopic test and studies them in hanging drops 

 under the microscope. If living cultures are used, it will be ob- 



