12 IMMUNE SERA. 



fuged fluid they added more sheep red cells; and, 

 in order to reactivate the serum, a sufficient amount 

 of alexin in the form of normal serum was also 

 added. The red cells, however, did not dissolve 

 there was no substance sensibilatrice. The next 

 point to prove was that this substance had actually 

 combined with the red cells. The red cells which 

 had been separated by the centrifuge were mixed 

 with a little normal salt solution after freeing them 

 as much as possible from fluid. Then a little alexin 

 in the form of normal serum was added. After 

 remaining thus for two hours at 37 C. these cells 

 had all dissolved. 



In this experiment, therefore, the red cells had 

 combined with all the substance sensibilatrice, 

 entirely freeing the serum of the same. That the 

 action was a chemical one and not a mere absorp- 

 tion was shown by the fact that red blood-cells of 

 other animals, rabbits or goats for example, exerted 

 no combining power at all when used instead of 

 the sheep cells in the above experiment. The 

 union of these cells, moreover, is such a firm one 

 that repeated washing of the cells with normal salt 

 solution does not break it up. 



The second important question solved by these 

 authors was this: What relation does the alexin 

 bear to the red cells ? They studied this .by means 

 of a series of experiments similar to the preceding. 



Experiment 2. Sheep blood was mixed with 

 normal, i.e. not haemolytic, goat serum. After a 



