BACTERIAL EMULSION. 29 



ture is washed off the media and with a thick walled capillary 

 pipette, with the end broken off squarely, the suspension is drawn 

 into the pipette. The open end of the pipette is firmly pressed 

 against a watch glass, as indicated in Fig. 7. When this is done 

 only a small crevice will remain between the end of the pipette 

 and the watch glass. The bulb is now compressed and the bac- 

 teria suspended in the salt solution are forced out through the 

 small crevices. This is done to break up the small clumps of bac- 

 teria. 



B. The organisms belonging to this class grow on the same 

 kind of media as do those belonging to the first group. The or- 

 ganisms of this group form cell aggregates that are not easily 

 broken up. The streptococci are the most important organisms 

 in this class. Streptococci frequently grow in long chains, 

 varying from two to thirty cocci. It is evident that a leuco- 

 cyte may be able to engulf one or more cocci without being able 

 to engulf a chain consisting of twenty or thirty cocci. The method 

 for breaking up ordinary clumps will not suffice for breaking up 

 chains of streptococci. 



While observing the opsonic index for streptococci in ery- 

 sipelas, the writer found it necessary to adopt some method to 

 break up the long chains of streptococci frequently isolated from 

 the lesions in erysipelas. This method consisted in the addition 

 of 2 to 3 c.c. of sterile salt solution to each twenty-four hour cul- 

 ture on glycerine, glucose agar. After washing off the growth, 

 the emulsion was put into a small test tube containing sterile 

 sea sand; the tube was sealed in a flame and shaken for one and 

 one-half hours in the shaking machine. The sand and emulsion 

 in the tube were centrifuged for one minute and the supernatent 

 fluid drawn off. In this way short chains, from two to four 

 cocci, were obtained. 



Another method was devised by Wright of Harvard University. 

 This method differs only from the one of Wright and Douglas in the 

 substitution of a paraffine block for the watch glass. When the 

 open end of the pipette is held against the paraffine the crevices 

 very small so that the chains are more completely broken up. 

 This method gives very satisfactory results. 



C. This class includes practically only one species of mi- 

 croorganisms, the bacillus of tuberculosis. The preparation of 



