278 The Phagocytic Power of the Blood 



The blood to furnish the serum is taken in a small bent 

 tube shown in Fig. 84. 



The blood flowing from the puncture is allowed to flow 

 into the bent end of the tube, into which it enters by cap- 

 illary attraction and from which it descends to the body of 

 the tube by gravity. At least one cubic centimeter of the 

 blood is required to furnish the serum. The ends of the 

 tube are closed in the flame and the tube stood in the ther- 

 mostat for fifteen to thirty minutes. Coagulation takes 

 place almost immediately, and the serum usually separates 

 quickly. If it does not do so, Wright recommends hanging 



Fig. 83. Removing last drops of saline solution (Miller). 



the curved arm of the tube over the centrifuge tube and 

 whirling it for a moment or two, when the clot is driven into 

 the straight arm of the tube and the clear serum appears 

 above. The tube is then cut with a file so that the serum can 

 be removed when needed. Mixing the factors concerned in 

 the test is a matter that requires practice and a steady hand. 

 It is best done, as recommended by Wright, in a capillary 

 tube controlled by a rubber bulb (Fig. 85). The object 

 of the experimenter is to take up into this pipette equal 

 quantities of the creamy layer of blood-corpuscles, of the 

 blood-serum, and of the bacterial suspension. Wright first 

 makes a mark with a wax pencil about i centimeter from the 

 end of the capillary tube. He first draws up the leukocytic 



