506 BACTERIOLOGY. 



drawn-out end of the pipette should be cut square. The 

 dilution of the serum can be made with sterile water, phys- 

 iological salt solution, or with bouillon. 



A number of glass cups (Klotze) are placed on a mount- 

 ing- board (p. 279). By means of the pipette these receive 10, 

 20, 30, 40, and 50 drops, respectively, of the sterile water. 

 The serum is then drawn up into the same pipette and one 

 drop of it is placed in each of the dishes. The dilutions 

 1: 10, 1: 20, 1: 30, 1: 40, 1: 50 are then prepared. The liquids 

 should be thoroughly mixed. This can be done expedi- 

 tiously and thoroughly by means of the pipette used. This 

 should be placed in a tumbler of water and the inside 

 washed by repeatedly drawing in water. The pipette thus 

 rinsed is now introduced into the weakest dilution (1 : 50) 

 and the liquid is drawn up. It is then forced out and this 

 operation repeated two or three times will bring about a 

 thorough mixing of the serum and water. The pipette is 

 again rinsed in clean water and the next dilution (1 : 40) is 

 mixed in the same manner. In this way each dilution is 

 rendered homogeneous. 



A number of clean cover-glasses are laid on the board. 

 A drop from each of the above dilutions is placed on the 

 corresponding cover-glass. Each drop is then inoculated 

 with a minute portion of an agar culture of the Eberth ba- 

 cillus. The culture should be recent, preferably 12 to 18 

 hours old. A concave slide, ringed with vaselin, is brought 

 over each cover-glass and the hanging-drops (p. 143), thus 

 prepared, are ready for examination. 



The specimens should be examined immediately, and at 

 the end of >^, 1 and 1^ hours. If agglutination does not 

 occur in this time it is unnecessary to prolong the observa- 

 tion. The undiluted serum should be tested at the same 

 time as the others. Moreover, one or more control hanging- 

 drops should be prepared in order to make certain that the 

 organism does not exist already clumped in masses in the 

 culture tube. In case the 1 : 50 dilution gives a marked ag- 



