ESTIMATION OF THE OPSONIC POWER OF THE BLOOD 169 



stances which he calls opsonins, and which have the power of 

 acting on pathogenic bacteria and altering them so that they can 

 be taken up and digested by leucocytes. These substances are of 

 great importance in that they appear to be the chief agents in the 

 production of some forms of immunity. Take, for instance, the 

 defence of the body against staphylococci. Leucocytes have no 

 power of taking up these organisms, and if the protection of the 

 body were entrusted to them alone a shght staphylococcic lesion 

 would be a very serious matter. But the blood contains a certain 

 amount of antistaphylococcic opsonin — a greater amount in some 

 persons and less in others — and this, by combining with the 

 staphylococci, renders them easily attacked by the leucocytes. It 

 follows that where we can measure the amount of opsonin present 

 we can form some estimate of the patient's resisting power against 

 the organism in question. It is found, for instance, that the serum 

 of patients in the early stages of staphylococcic diseases, such as 

 pustular acne or boils, is usually very deficient in antistaphylococcic 

 opsonins, whilst when cure takes place the amount rises above 

 normal. These opsonins are probably specific — i.e., each organism 

 has its own appropriate opsonin : that for tubercle, for example, 

 is devoid of action on staphylococci, and vice versa. 



The method given is practically that used by Wright. It is a 

 general method, and is available for almost any organism, the only 

 points of difference arising in the preparation of the emulsion of 

 bacteria, which differs somewhat with the various organisms. 

 The method is a relative one. Two tests are made, one with the 

 serum of the patient, and one with that of a healthy person, and 

 the results of the two are compared in the manner to be described 

 subsequently. 



The process is not altogether an easy one, and requires a con- 

 siderable amount of patience and some practice. Yet I know that 

 several practitioners have been able to accomplish it, and as the 

 test is of great importance and interest, and as it requires little 

 in the way of apparatus, it seems right to give a description of it 

 here. 



The requisites are — 



1. The serum of the patient to be tested. 



2. That of the healthy person taken as a control. 



These are best collected in Wright's curved pipettes (see p. 35). 

 They must be taken at approximately the same time (within a 

 few hours), since the opsonin gradually becomes inert. The test 



