264 



METHOD OF EXTINCTION 



It has an advantage over Wright's method even in cases in 

 which the bacteria are not dissolved in the serum or leucocytes, 

 in that it provides a definite measure of the amount of opsonin 

 present, which the ordinary method does not do, as is shown by 

 the fact that the opsonic index of a mixture of equal parts of 

 serum and normal saline solution is more than half that of 

 undiluted serum. 



An enormous number of opsonic determinations have been 

 carried out, and the results have been of extreme interest. It is 



3000 



2,800 



2,600 



2,400 



2.200 



2,000 



1.800 



1.600 



1,400 



1,200 



1.000 



800 



600 



400 



200 



IB 17 19 21 23 25 27 29 31 2 4 6 8 10 12 14 



* = Leucocytes per cubic mm. (figures at right of chart). 

 - = Opsonic power of serum. 



= Bacteriolytic power of serum. 



t-- - = Agglutinative power of serum. 



FIG. 58. INFLUENCE OF INOCULATION OF TYPHOID VACCINE ON THE OPSONIC 

 POWER OF THE SERUM OF A RABBIT, AS SHOWN BY THE DILUTION 

 METHOD. (After Klien.) 



found that the indices of healthy persons is approximately the 

 same, and does not vary much from day to day. In the case of 

 tubercle a very large number of determinations of the indices of 

 normal persons have been made, and it is found that, with one 

 or two exceptions, due perhaps to accidental errors in technique, 

 they all lie between o\S and 1-2, taking i as a standard. In reality 

 they agree very much more closely than this, for the great 



