OPSONIC ACTION 165 



II. ABSORPTION BY SERUM PRECIPITATE 



It has been now well established by the researches of 

 Moreschi, Gay, and others, including ourselves (vide p. 133) 

 that a precipitate produced by a precipitin acting on the 

 homologous serum has the property of fixing various com- 

 plements. Certain molecules in the serum used for injecting 

 the animal in order to develop the precipitin give rise to 

 anti-molecules, and the combination of the two takes up 

 complement, as is readily shown by haemolytic tests. The 

 anti-molecules, so far as the fixation of complement is con- 

 cerned, behave like immune-bodies, though certain differ- 

 ences obtain, as we have already pointed out (p. 157). 

 We have inquired whether this combination of serum- 

 receptors plus immune-bodies also absorbs the opsonins 

 of normal serum. The experiments are carried out in 

 a manner analogous to the previous, a serum precipitate 

 being substituted for red corpuscles treated with immune- 

 body. 



The precipitate is produced by adding 0-05 c.c. of ox's 

 serum heated at 55 C. to 1-5 c.c. of precipitin (anti-serum 

 produced by injecting a rabbit with ox's serum) in 20 c.c. of 

 0-85 NaCl solution. The mixture is allowed to stand over- 

 night, and next day the precipitate is separated and washed 

 several times in salt solution. After a final centrifugaliza- 

 tion the fluid is removed as completely as possible and 

 2 c.c. of guinea-pig's normal serum is added to the precipi- 

 tate. The precipitate is well shaken up in the serum, and 

 the mixture is placed in the incubator for one and a half 

 hours at 37 C. The mixture is then centrifugalized, and 

 the clear serum is pipetted off from the precipitate. As 

 before, the resulting serum will be spoken of as treated 

 serum, and its properties will be compared with those of 

 heated and of normal serums. 



