296 



AGGLUTININS 



in a diluent, such as normal salt solution or broth. This may be per- 

 formed by placing the diluent in a test-tube and rubbing the loop over 

 the glass just at the margin of the fluid, the bacteria being gradually 

 emulsified and floated into the diluent. When larger quantities of emul- 

 sion are desired, as for making the macroscopic test, 5 c.c. of diluent may 

 be poured upon the culture and the growth washed off with the aid of 

 the platinum loop. The emulsion is gently shaken and removed to a 

 second tube, when unresolved bacterial clumps will sink to the bottom. 

 In other cases the emulsion may be centrifuged for a short time or fil- 

 tered through sterile filter-paper. Sufficient salt solution is added .to 



FIG. 81. A SATISFACTORY CULTURE FOR 

 THE MICROSCOPIC AGGLUTINATION 

 REACTION. X 430. 



This shows a satisfactory culture of 

 the proper density and free of clumps of 

 bacilli. (Twenty-four hour culture of 

 Bacillus typhosus grown at room tem- 

 perature.) 



FIG. 82. AN UNSATISFACTORY CULTURE 



FOR THE MICROSCOPIC AGGLUTINA- 

 TION REACTION. X 430. 



The culture is rather too dense and 

 shows considerable spontaneous or false 

 agglutination of the bacilli. (Twenty- 

 four hour culture of Bacillus typhosus 

 grown at 37 C.) 



give the emulsion a density equal to that of a rich twenty-four-hour 

 bouillon culture. 



A permanent suspension of microorganisms for the macroscopic 

 test may be prepared in the following manner (Oxford University) : 



The bacillus (B. typhosus, B. paratjrphosus, etc.) is grown for twenty- 

 four hours at 37 C. in ordinary veal peptone bouillon in large Erlen- 

 meyer flasks partly filled (1 liter of bouillon in a one and a half liter 

 flask). 



Before use the flasks of bouillon are sterilized in the autoclave at 



