The Washed Leukocytes 



277 



barium sulphate precipitate. By careful comparison of the 

 suspension with the standard tube, and the addition of 

 more of the salt solution or of the bacteria, as may be 

 required, one can arrive at fairly uniform results in a few 

 moments. 



The Washed Leukocytes. It is not necessary to have 

 the leukocytes free from admixture with the erythrocytes, 

 but it is necessary to have large numbers of them. They 

 are collected by citrating the blood so as to prevent coagula- 

 tion, and then separating the citrated plasma from the 

 corpuscles by centrifugalization. 



The hands of the patient are washed, and a piece of elastic 

 rubber tubing or some other convenient fillet wound about 

 the thumb or a finger to produce venous 

 congestion. With a convenient lancet 

 (Wright uses a pricker made by drawing 

 a bit of glass tubing or a glass rod to a 

 fine point in the flame) a prick is made 

 about a quarter inch from the root of 

 the nail (Fig. 81). From this the blood 

 is permitted to flow into small test-tubes 

 previously filled about three-fourths with 

 1.5 per cent, sodium citrate solution. 

 The blood and citrate solution are mixed, 

 and the tubes placed in a centrifuge, 

 balanced, and centrifugalized until the 

 corpuscles are collected at the bottom 

 of the tube (Fig. 82). The citrated 

 plasma is now withdrawn and replaced 

 with 0.85 per cent, sodium chloride solu- 

 tion, through which the corpuscles are 

 distributed by shaking. The tubes are 

 now again centrifugalized until the corpuscles are collected, 

 when the saline is removed carefully, the last drop from 

 the back of the meniscus (Fig. 83). In the corpuscular 

 mass that remains the leukocytes form a thin creamy layer 

 on the top. 



The serum to be tested and the normal serum for 

 comparison are secured in the same manner, the former 

 from the patient, the latter from the operator. As it is 

 advisable to wound the patient but once, the tube for 

 obtaining the serum should be filled at the same time that 

 the citrated blood is taken. 



Fig. 82. Tube of 

 blood and citrate 

 solution before and 

 after centrifugaliz- 

 ing (Miller). 



