280 



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. 78. 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. 79. 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. 



(4) To emulsify a culture of the plague bacillus or any other micro- 

 organism that displays a strong tendency to undergo "spontaneous" 

 agglutination, distilled water or 1 : 1000 salt solution should be used. 



(5) In the case' of a culture of tubercle bacillus, the growth can be re- 

 solved into its elements by prolonged trituration in normal salt solution, 

 and any residue or unresolved clumps removed by centrifugalization. 

 A less laborious and dangerous method is to use the tubercle powder of 

 Koch, which is obtained by reducing dried tubercle cultures to a fine 



