SYPHILIS I 19 



acquire no power whatever over human corpuscles. The 

 power of haemolyzing alien corpuscles is, therefore, a rare 

 attribute of the serum of a normal animal, but can be acquired 

 by injecting the animal (" immunizing " it) with the corpuscles 

 it is desired to dissolve. 



Further investigation shows that this haemolytic power is 

 dependent on the presence of two substances, one of which 

 occurs in normal serum, whilst the other is formed as a result 

 of the injection. The first is called complement. It occurs 

 in all serum, though in varying amount; it is easily destroyed 

 by heat (55 C. for half an hour, or 60 C. for ten minutes), 

 and it disappears spontaneously in a few days at the room 

 temperature.* It is therefore a fragile substance, and is allied 

 to the enzymes. The second is called amboceptor. It. rarely 

 occurs in normal serum, but is formed when alien corpuscles 

 are injected: thus, a normal rabbit serum contains no ambo- 

 ceptor for human corpuscles, but acquires it after two or 

 three injections. Amboceptor is not readily destroyed, resist- 

 ing heat that will destroy every trace of complement, and it 

 remains for months in serum kept at the room temperature. 

 Both these substances are essential for haemolysis, and if one 

 or other is present alone, no solution will occur. The proof 

 of these statements is simple, and depends on a series of 

 experiments which, if the materials are at hand, may be 

 readily repeated. The requisites are, fresh human serum, 

 fresh serum from a normal rabbit, fresh serum from a rabbit 

 which has been injected with human corpuscles, the same 

 three sera heated to 60 C. for ten to fifteen minutes, and, 

 lastly, an emulsion of washed human corpuscles. This is pre- 

 pared as follows : Prepare normal saline solution containing 

 0-9 per cent, salt and about 2 or 3 per cent, sodium citrate. 

 Into about 10 c.c. of this solution drop a small amount (10 to 

 20 drops) of blood from a finger-puncture, and centrifugalize 

 until the corpuscles are deposited and the supernatant fluid 

 clear. Pour off the supernatant fluid and replace it by 

 ordinary normal saline, mix well, centrifugalize down again, 

 and repeat the process once more. This will give you a 

 deposit of corpuscles washed from all trace of serum. Pre- 

 pare a 10 per cent, emulsion of these corpuscles in normal 



* Its stability varies greatly in different animals. Human complement 

 disappears only slowly. 



