MICHIGAN ACADEMY OF SCIENCE. 149 



tec'hnic for determining the bactericidal action of blood serum, this method 

 of testing the blood's power, too, was abandoned and the opsonic index 

 substituted. 



As to the future of artificial imunity induced by bacterial inoculation 

 Wright has recently delivered a remarkable forecast. Up to the present, 

 he said, the conmiunity has devoted most of its energy to trying to kill bac- 

 teria outside the organism by hygiene and disinfection; but disease germs 

 still lie in wait in countless millions in our food and in the air we breathe; 

 like the ]ioor, they will always be with us. The next advance in sanitary 

 science will be to fight the disease within the organism, either by fortifying 

 it in advance of infection, or before the infection has attained dangerous 

 headway. The physician of the future must be an "immunizator." 



THEORY OF OPSONINS. 



Brought to its simplest terms Wright's theory of opsonins holds that an 

 individual's blood serum contains, among other protective substances, one, 

 opsonin, which acts directly upon pathogenic bacteria in such a manner as 

 to prepare them for destruction by the protective body cells or phagocytes. 

 Opsonins are assumed to be specific, as for example, one for the pyogenic 

 staphylococci, for the streptococcus, the tubercle bacillus, and so on. \Vhen 

 present in normal amount and when the free circulation of the serum con- 

 taining opsonin is in no way impeded, pathogenic bacteria fail to excite 

 morbid effects. But with a lowering of the blood serum's opsonic power 

 against a given bacterium or through failui'e of the serum to reach a certain 

 focus, the characteristic disease of that particular bacterium may occur 

 because of the inability of the phagocyte to envelop and destroy it, this fail- 

 ure arising from no lessened activity or power of the phagocyte itself, but 

 because the opsonin does not act upon the bacterium with sufficient energy 

 to prepare it for destruction by the protective body cell. 



By mixing, in glass, under laboratory conditions, human leucocyets 

 washed free from serum, an emulsion of a certain bacterium, and the blood 

 serum to be tested, according to directions which Wright and his followers 

 have freely published in the medical periodicals of Great Britain, one may 

 evaluate the opsonic power of that particular serum against that particular 

 germ. For the leucocyte, washed free from serum, will not actively ingest 

 the bacteria; and the number of bacteria taken up in a given number of 

 leucocytes in the presence of a certain serum indicates a measure of the opsonic 

 value of the serum under obervation. The capacit}^ of a serum to produce 

 phagocytosis is spoken of as its "phagocytic index," and a comparison of the 

 phagocytic index of the serum with another or several from presumably nor- 

 mal individuals, gives the so-called "opsonic index." It is the determination 

 of the opsonic index that forms the basis upon which Wright gets his indi- 

 cation for treatment and, in the course of treatment, graduates the dose of 

 the bacterial virus and its repetition. 



It has been found that in case of a low opsonic index against a pathogenic 

 bacterium, particularly one belonging to the group of pus producers, the 

 index can be raised by the subcutaneous injection of a relatively small dose 

 of the corresponding germ; and not only does the opsonic index as ascer- 

 tained in the- laboratory test rise, but the increased resistance against that 

 germ is generally shown by a condition of general well being and an improve- 

 ment in whatever local lesion the microbe may have caused. Repeated at 

 proper intervals and in correct doses this preparation of the corresponding 



