150 APPENDIX. 



cells, for example, by injecting a rabbit with sheep 

 blood cells. This rabbit serum would then be 

 specifically directed against sheep blood cells. Let 

 us inactivate this serum, by heating it to 55 C., so 

 that now it requires the addition of a fresh normal 

 serum to exert its solvent effect. For this purpose 

 we can again use fresh, normal guinea-pig serum. 

 When, then, we mix sheep blood cells with our 

 specific immune serum (against sheep blood cells) 

 and with the complement, i.e., with fresh normal 

 guinea-pig serum, all three factors unite, and bring 

 about destruction of the red blood cells. This is 

 manifested by the blood cells dissolving and 

 giving off their haemoglobin to the rest of the 

 fluid. 



Let us now suppose we have carried out the first 

 part of this experiment, that with the typhoid bacilli, 

 and have left typhoid bacilli, specific typhoid serum 

 and complement in contact for several hours in a 

 warm place in order to cause the three factors to 

 combine. At the end of this time let us add sheep 

 blood cells and the specific serum directed against 

 sheep cells, but let us add no further complement, 

 because the fresh guinea-pig serum was able, as we 

 saw, to serve as as complement also for the blood 

 combination. The mixture is again placed in a 

 warm place for several hours, and then for twenty- 

 four hours in the refrigerator, after which it is ex- 

 amined. We shall find that no haemolysis has 

 occurred, from which we conclude that the previous 

 combination (typhoid bacilli, immune scrum and 



