QUALITATIVE BACTERIOLOGICAL ANALYSIS. 183 



then difficult, if not impossible, to focus the clumps accurately, 

 consequently I prefer to open the capillary tubes and examine 

 the contents in the manner described ; the clumps are then seen 

 perfectly, as there is not time for them to settle down to the 

 bottom of the drop. Sometimes when the capillary tubes are 

 examined with the naked eye a deposit is seen at the bottom 

 of the tube, and without practice mere sedimentation of the 

 bacilli might be confused with agglutination, To avoid this 

 source of error, the tubes may be opened and the contents 

 examined by the hanging-drop method ; or more simply, the 

 question of agglutination may be decided by placing the tubes 

 horizontally on a table for five or ten minutes. If the clumps 

 are the result of true agglutination, the masses at the bottom of 

 the tubes will not have changed their shape, and the outline will 

 be sharp and convex ; if, however, the clumps have been formed 

 merely by sedimentation, the masses will have changed their 

 shape and the upper margin will be oblique, gradually tapering 

 off* to the lower side of the tube. 



The results obtained by the twenty -four hours observation 

 are more delicate than those obtained at the end of two hours ; 

 but as many bacteriologists perform the test in the hanging- 

 drop and limit the observation to two hours, it is always well to 

 examine the tubes at the end of this time, so that the results 

 may be compared with those obtained by other observers. 

 Temperature has an effect on the agglutinative action of anti- 

 typhoid serum. Biberstein found that a serum diluted 1-14,000 

 clumped the B. typhosus when the preparation was kept at 37 

 C., but at the room temperature the agglutinative action was 

 limited to a dilution of 1-12,000. I obtained very similar 

 results with my own experiments. The serum always acted in 

 a slightly higher dilution at 37 C. than at the room tempera- 

 ture. Consequently when results are stated it is always 

 important to give the temperature at which the experiment 

 was made. 



Again, the results obtained with an emulsion made from a 

 twenty-four hours agar growth of B. typhosus are not compar- 

 able with those obtained with a twenty-four hours broth culture 

 of B. typhosus. I have found very marked differences in the 

 results obtained by the two methods when applied to the same 



