The Complement 321 



momentary spraying with chlorid of ethyl will make the 

 operation entirely painless. Some prefer to use the iodin 

 without the preliminary washing, believing that soap 

 makes it difficult for the iodin to effect satisfactory dis- 

 infection of the skin. The sterilized needle is thrust into 

 the vein, care being taken that the vein is not too com- 

 pressed and the point of the needle thrust entirely through 

 instead of into it. From 15 to 25 c.c. of blood may be with- 

 drawn into a large syringe or may be allowed to flow into a 

 sterile test-tube. The blood, however secured, is permitted 

 to coagulate and the clear serum removed by a pipet, or the 

 clotted blood is placed in a centrifuge tube and whined, so 

 that clear serum is secured in a few minutes. 



As normal human blood-serum, when fresh, contains a 

 certain amount of complement which would interfere with 

 the success of the experiment, the serum is next placed in a 

 test-tube and kept in a water-bath between 55 to 58 C. for 

 a half -hour. This degree of heat destroys the complement 

 and leaves the complement-fixing substance uninjured. The 

 serum is now ready for use. 



(3) The Complement. The complement universally em- 

 ployed is contained in the blood of a healthy adult guinea-pig. 

 To obtain it a piece of cotton moistened with ether or chloro- 

 form is held to the guinea-pig's nose until it becomes uncon- 

 scious, when the head is forcibly extended and a longitudinal 

 incision made through the skin of the neck. The skin is then 

 drawn back between the finger, on the one side, and the thumb, 

 on the other side, of the operator's left hand, while, with a 

 sharp knife held in the right hand, he cuts through all of the 

 tissues of the neck down to the spinal column and thus opens 

 both carotid arteries. The spurting blood is caught in a 

 sterile Petri dish and the animal permitted to bleed to death. 

 The blood soon coagulates when undisturbed, and in a short 

 time clear serum exudes from the clot. As, however, the 

 complement seems to be at least in part derived from the 

 corpuscles, the serum should not be removed as soon as it 

 forms, but permitted to remain in contact with the clot for 

 three hours. If it is desired to save time, the clot, as soon as 

 formed, may be cut into strips and placed in the tubes of a 

 centrifuge and whirled for a half -hour. This secures a 

 greater quantity of the serum and at the same time gives it 

 its full value, probably by injuring the leukocytes. 



Such serum containing the complement is useful for twenty- 



