196 OPSONIC INDEX 



An index taken at one time by one person and later by another, and so 

 on, will not be of as much value as when all are taken by the same worker, 

 who brings practice, skill, and conscientious care to his aid. 



Precautions in Technic. 1. Proper controls should be used. When 

 dealing with the tubercle bacillus, the staphylococcus, or any other 

 saprophyte of the external surfaces, or with any pathogenic organism 

 with which we have normally no relations, the serum of a normal in- 

 dividual or the mixed serum of a number of normal persons will furnish 

 the standard of comparison. When, on the other hand, we are dealing 

 with intestinal bacteria or with a saprophyte of the mucous membrane, 

 where, as a rule, any relation with them will be denied, it is difficult to 

 establish a standard of health. Pooled serum is, therefore, necessary, 

 and will furnish a standard for comparison for the purpose of measuring 

 the fluctuations that may occur in the patient's blood. 



2. A reasonable degree of phagocytosis should occur in the control 

 serum. This is one of the main drawbacks to the value of the method 

 for certain pathogenic organisms, as the pneumococcus, meningococcus, 

 streptococcus, etc., may resist phagocytosis in normal serum, and thereby 

 show abnormally high indices with immune serum. 



3. Efforts at spontaneous phagocytosis should be suppressed in 

 order to measure more accurately the opsonin, as shown by the degree 

 of phagocytosis independent of the inherent activities of the cell itself. 

 Spontaneous phagocytosis can largely be overcome by using 1 per cent, 

 solution of sodium citrate such as is used for the collection of leukocytes. 



4. The ingest of a sufficiently large number of phagocytes should be 

 counted. As a general rule, 100 cells should represent the minimum. 



TECHNIC 



The necessary constituents for making the test are as follows: 



1. The patient's serum and normal serums to serve for the control. 



2. A bacterial emulsion. 



3. A suspension of washed human leukocytes in normal salt solution. 

 Collection of Patient's and Control Serum. 1. The blood is col- 

 lected in a Wright capsule, as described in Chapter II. 



2. Care must be taken not to heat the blood when sealing the tube. 

 In drawing off the serum, avoid an admixture of corpuscles, as these may 

 lower the opsonic index. 



3. If coagulation is incomplete or the serum has not been well sep- 

 arated, the clot may be broken up gently with a platinum wire and the 



