170 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



should be made not more than three or four days after the blood 

 has been taken. 



3. The emulsion of bacteria. In the case of tubercle an emul- 

 sion of dead bacilli in normal saline solution is employed. This 

 can be obtained ready prepared ^rom Messrs. Allen and Hanbury. 

 If you wish to prepare it for yourself, it is necessary to make a 

 culture of tubercle bacilli in glycerinated broth ; incubate for two 

 months ; boil to kill the bacilli ; filter through filter-paper ; wash 

 with normal saline solution ; let the bacillary mass drain as dry 

 as possible, and then place it in a sterile tube and immerse in 

 boiling water for half an hour to make certain of its sterility. 

 The yellowish mass thus obtained will keep indefinitely, and will 

 serve for many tests. To prepare the emulsion from this, take a 

 small portion (about as big as a grain of rice) and place it in a 

 small agate mortar, and grind it up with the pestle; then add 

 normal saline drop by drop until about 2 c.c. have been added, 

 continuing to grind meanwhile. This gives an emulsion which 

 contains isolated bacilli as well as clumps. These latter must be 

 got rid of, and to do this it is necessary to centrifugalize for three 

 or four minutes. 



The staphylococcic emulsion is .prepared by taking an agar 

 culture not more than twenty-four hours old, adding some normal 

 saline solution, and shaking gently so as to wash off the growth. 

 When the emulsion is made it must be pipetted off into a small 

 tube and centrifugalized for a few minutes, to get rid of clumps. 

 The emulsion must not be too thick, otherwise the leucocytes will 

 take up an uncountable number of cocci ; the proper density can 

 only be judged by experience, but the emulsion should only be 

 faintly opalescent. Emulsions of pneumococci and other organisms 

 are made in the same way. 



4. An emulsion of living leucocytes. To prepare this take 

 about 10 c.c. of normal saline solution containing ^ per cent, of 

 sodium citrate, to prevent the coagulation of the blood. This must 

 be freshly prepared (or kept sterile, which is inconvenient), and 

 the simplest method is to use " soloids " prepared for the purpose 

 by Messrs. Burroughs and Wellcome (No. 2,456) ; one of these 

 dissolved' in 10 c.c. of water will yield the solution required.* 

 This is put into a centrifugalizing-tube and warmed to blood-heat. 

 A healthy person is then pricked in the ear or finger, and his 

 blood is allowed to drop into the fluid until i c.c. or more has 



* This very convenient method was suggested by Dr. Whitfield. 



