i:.\< TKRIAL EMULSIONS. 43 



BACTERIAL EMULSIONS. 



Wright, in his technique, attempts in every case to break 

 ii] > all clumps of bacteria and tries to get such strength of suspen- 

 sion that the number of bacteria per leucocyte can be easily 

 determined. With certain organisms trial tests are necessary. 

 After this, the suspension may be diluted or bacteria added as 

 may be indicated. 



Most investigators have experienced difficulty in obtaining 

 suitable suspensions and Wright himself has changed his tech- 

 nique for making bacterial suspensions from time to time. The 

 difficulties that have been experienced are of two kinds: those 

 dealing with the strength of the bacterial suspension, and those 

 concerning the condition of the microorganisms in the suspension. 



Difficulties depending upon the strength of the bacterial 

 suspension. Numerous investigators have given definite figures 

 to be obtained for the phagocytic index with normal serum. In 

 most cases it is desirable that the phagocytic index for normal 

 serum be between six and fifteen. Simon has found that when 

 the emulsion contains between 666,000 and 2,000,000 microor- 

 ganisms per cubic millemeter the best results are obtained. Re- 

 cently Walker has emphasized certain facts that must be taken 

 into consideration in determining the strength of the bacterial 

 emulsion. If the suspension does not contain enough bacteria 

 to exhaust all the opsonin in the strongest serum, a certain amount 

 of opsonin will, according to Walker, be lost in the estimation of 

 the opsonic index. In order to get the right strength of bacterial 

 suspension, Walker tests the same with serum diluted 1 to 30 

 and 1 to 15. If the 1 to 15 dilution of serum shows a phagocytic 

 index twice as great as that obtained in the 1 to 30 dilution then 

 enough bacteria are present in the suspension. Too such a sus- 

 pension he, however, adds more of the culture, because having 

 more bacteria than are absolutely necessary will not change the 

 opsonic index but will certainly furnish enough bacteria to ex- 

 haust the serum of its opsonin. Only with the staphylococci 

 will a too heavy suspension effect the true index. This Walker 

 believes is due to the action of a product of bacterial growth. 

 To overcome the excessive phagocytosis when heavy suspensions 

 of bacteria are used, Walker dilutes serum. However, as has been 



