360 STUDIES IN IMMUNITY. 



To each tube there is then added one-thirtieth of a cubic centi- 

 meter of normal rabbit alexin (serum from blood obtained the day 

 before). Fifteen minutes later 0.3 of a cubic centimeter of sen- 

 sitized ox blood is added to each tube. This sensitized blood is a 

 mixture of one part of carefully washed ox blood * to five parts of 

 heated rabbit > ox serum. 



There is complete hemolysis in tubes 1, 4, 5 and 6; partial hemoly- 

 sis in tube 2; and no hemolysis in tube 3. The alexin, therefore, has 

 remained free in tubes 1, 4, 5 and 6 containing no precipitate, has 

 been partially absorbed in tube 2 containing a moderate precipitate, 

 and has been completely absorbed in tube 3 that contains the largest 

 precipitate. In other words, the greater the amount of precipitate 

 the greater the alexin absorption and corresponding absence of 

 hemolysis. 



As may be imagined, this experiment may be performed some- 

 what differently. A mixture containing the albuminous precipitum 

 and the sensitized corpuscles may be made and the alexin sub- 

 sequently added. Under these conditions we should expect that 

 both sensitized elements that are avid of alexin, namely, the pre- 

 cipitate and the corpuscles, would struggle to obtain the alexin, 

 and hemolysis would be more or less inhibited or even entirely pre- 

 vented if the dose of alexin were not too large. To produce these 

 conditions we may place in tube A small amounts of well-washed 

 ox blood (0.05 of a cubic centimeter) and of ox serum (0.025 of a 

 cubic centimeter), and then add a very large dose of heated rabbit 

 > ox serum (2.5 c.c.). A few seconds later let us add rabbit alexin 

 (one-thirtieth of a cubic centimeter). There is no hemolysis, as the 

 precipitum has absorbed all the alexin. In a control tube B pre- 

 pared at the same time, and containing the same components except 

 the ox serum, hemolysis is complete, as no precipitate forms. All 

 that is necessary to produce hemolysis in tube A is to add a small 

 additional dose of alexin. 



We have already noted that considerable immune serum is 

 necessary to obtain an abundant precipitate with ox serum. Con- 

 sequently, if a dose of rabbit > ox serum barely sufficient to sensitize 



* This blood had been carefully washed in normal salt solution and then 

 restored to its original volume; it corresponds, then, to blood in which the original 

 serum is replaced by salt solution. 



