244 



SCIENCE 



[N. S. Vol. XXIX. No. 737 



take up what he and his followers then 

 called "fixateur " thereby are made phago- 

 cytable. It is not impossible that further 

 analysis of the mechanism of phagocytosis, 

 under the guidance of the opsonic theory, 

 will lead to this as the final result. At all 

 events the failure to recognize the inter- 

 action of the two elements in the opsonic 

 function of serum and the great difference 

 in their combining properties is responsible 

 for many of the divergent results of vari- 

 ous investigators. 



While normal blood contains only com- 

 paratively small amounts of heat-resistant 

 opsonic substances, each unquestionably 

 possessed of more or less well-marked 

 specific affinities, the blood in conditions of 

 acquired immunity may be richly charged 

 with newly formed thermostable opsonic 

 substances with marked specific affinity 

 for the object against which the immunity 

 is directed. Injections of suitable animals 

 with bacteria or with alien red corpuscles 

 cause specific opsonins to form; in human 

 beings new opsonins arise as the result 

 either of spontaneous infections or of the 

 artificial introduction of killed bacteria 

 and various bacterial products. 



The opsonin content of the blood may 

 be measured more or less accurately, 

 either by means of the opsonic index or 

 by determination of the highest dilution of 

 the serum at which opsonic effect is still 

 obtainable and comparing it with some 

 normal standard. Speaking only in gen- 

 eral terms, the opsonic index of Wrig'ht 

 with respect to a given bacterium is ob- 

 tained by comparing the number of bac- 

 teria taken up under the influence of the 

 serum of the person or animal in question 

 with the number taken up under the in- 

 fluence of the corresponding standard of 

 normal serum under conditions that are 

 as comparable as they possibly can be 

 made. 



By following the fluctuations of the op- 



sonin content at frequent intervals impor- 

 tant facts have been learned in regard to 

 the laws of opsonin production. In the 

 language of immunology any substance 

 capable of giving rise to antibodies in 

 suitable animals is called an antigen. 

 Microbes and various microbic deriva- 

 tives, cells, red corpuscles and serum 

 may contain several antigens and incite 

 the formation of more than one kind of 

 antibody so far as indicated by the usual 

 modes of antibody effect. Thus the 

 proper single injection in a suitable ani- 

 mal of typhoid bacilli or of alien red cells 

 is followed usually by the appearance in 

 the blood of increased amounts of lysins 

 (lytic amboceptors), agglutinins and op- 

 sonins for the particular cells injected. 

 Usually all three of the bodies mentioned 

 are not increased in the same proportions 

 so far as determinable by our present 

 methods of measurement, but they all com- 

 monly follow the same general course, 

 which seems to hold good for antibodies in 

 general: For the first day or two or three 

 there is often, but apparently not always, 

 a fall below normal in the amount of the 

 specific antibodies in the serum; this 

 period is called the negative phase and is 

 succeeded by a steady rise above the 

 normal, which, as a general rule, reaches its 

 maximum about the eighth to twelfth day 

 when there is a fall, the apex of the curve 

 being sometimes quite sharp, at other times 

 more rounded, and then begins a gradual 

 return to the normal. 



It is important to note that the fall be- 

 low normal, the negative phase, is specific, 

 that is, affects only the normal opsonin, 

 and by inference the other antibodies, for 

 the particular bacterium or coi-puscles in- 

 jected, a clear indication, it strikes me, 

 that there are several normal antibodies, 

 each with specific affinities and probably 

 not different from the corresponding body 

 formed when the machinery of immuniza- 



