ESTIMATION OF THE OPSONIC POWER OF THE BLOOD 2OI 



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 should be made not more than three or four 

 days after the blood has been taken. 



3. The emulsion of bacteria. In the case of tubercle an 

 emulsion of dead bacilli in normal saline solution is employed. 

 This can be obtained ready prepared from Messrs. Allen and 

 Hanbury. If you wish to prepare it for yourself, it is neces- 

 sary to make a culture of tubercle bacilli in glycerinated 

 broth; incubate for two months; boil to kill the bacilli; filter 

 through filter-paper; wash with normal saline solution; let 

 the bacillary mass drain as dry as possible, and then place it 

 in a sterile tube and immerse in boiling water for half an hour 

 to make certain of its sterility. The yellowish mass thus 

 obtained will keep indefinitely, and will serve for many tests. 

 To prepare the emulsion from this, take a small portion 

 (about as big as a grain of rice) and place it in a small agate 

 mortar, and grind it up with the pestle; then add normal 

 saline drop by drop until about 2 c.c. have been added, con- 

 tinuing to grind meanwhile. This gives an emulsion which 

 contains isolated bacilli as well as clumps. These latter must 

 be got rid of, and to do this it is necessary to centrifugalize 

 for three or four minutes. 



The staphylococcic emulsion is prepared by taking* an agar 

 culture not more than twenty-four hours old, adding some 

 normal saline solution, and shaking gently so as to wash off 

 the growth. When the emulsion is made it must be pipetted 

 off into a small tube and centrifugalized for a few minutes, to 

 get rid of clumps. The emulsion must not be too thick, other- 

 wise the leucocytes will take up an uncountable number of 

 cocci; the proper density can only be judged by experience, 

 but the emulsion should only be faintly opalescent. Emul- 

 sions of pneumococci and other organisms are made in the 

 same way. 



