INFECTION AND IMMUNITY 349 



ence of enterokynase; that rennet coagulates casinogen 

 only in the presence of calcium salts, and the coagulating 

 ferment of the blood transforms fibrinogen only in the 

 presence of a calcium salt. 



The indirect reactions are chiefly known in reference to 

 the solution of formed bodies cells, etc. and were first 

 studied with reference to the hemolysis or the solution 

 of red blood corpuscles by immune hemolytic serum. 



Such a serum may be prepared by defibrinating blood, 

 sedimenting the corpuscles with the aid of a centrifuge, 

 pouring off the plasma, adding an equal volume of phy- 

 siological salt solution, shaking up the corpuscles so as to 

 wash them, recollecting them by means of the centrifuge, 

 decanting the solution, replacing it by a similar volume 

 of salt solution, again shaking the corpuscles in the fluid, 

 and repeating the process once more. After being thus 

 washed, and finally distributed through a small quantity 

 of salt solution, the suspension is injected into the abdom- 

 inal cavity of a rabbit. The best treatment seems to be 

 to administer about six doses, increasing from 3 to 6 c.c., 

 the injection being made bi-weekly, always with fresh 

 material. In getting rid of these corpuscles, which act 

 as an antigen, an antibody known as an immune body or 

 amboceptor is formed. By French writers, for reasons 

 later to be explained, it is also known as the fixateur or 

 substance sensibilisatrice. 



When washed red corpuscles, prepared as has been 

 described, but in a 5 per cent, suspension in physiolog- 

 ical salt solution, are added to diluted blood serum from 

 an animal treated as has been suggested, and therefore 

 containing the specific amboceptor, scarcely any change 

 will be noted, and if the amboceptor serum have been 

 previously heated for an hour to 55 C., no result at all 

 will be effected. If, however, to the mixture that thus 

 appears to be indifferent there be added a small quantity 

 of the blood-serum of a freshly killed guinea-pig, the 

 corpuscles quickly hemolyse and dissolve. Upon inves- 

 tigation, the blood serum of the normal guinea-pig is 



