EXAMINATION OF THE BLOOD 71 



large quantity of blood may be obtained by puncture of a vein ; 

 this is the only satisfactory method, and should be that followed 

 whenever practicable. The skin over a vein in the forearm or 

 on the dorsum of "the foot having been sterilised by being 

 painted with tincture of iodine, the vein is made turgid by 

 pressure, and the needle of a syringe of 10^15 c.c. capacity, 

 sterilised by boiling, is plunged obliquely through the skin by 

 the side of the vessel into the lumen of which the point can then 

 be passed. (If a bandage has been used to make the vein 

 turgid, pressure should be maintained on the puncture, after the 

 needle has been withdrawn, until the bandage has been removed ; 

 otherwise a hsematoma may be formed by leakage from the 

 vessel.) Several cubic centimetres of blood can thus be with- 

 drawn into the syringe. Some of the blood {e.g., 5 c.c.) should 

 be added to small flasks containing 50 c.c. of bouillon ; the rest 

 may be used for smearing the surface of agar tubes, or may be 

 added to melted agar at 42° O, which is then plated. The 

 flasks, etc., are then incubated. By this method cultures can 

 often be obtained, especially in severe conditions such as ulcera- 

 tive endocarditis, streptococcus infection, etc. Part of the blood 

 may be incubated by itself for twenty-four hours and cultures 

 then made. Needless to say, the inoculations of media must be 

 done at the bedside, as of course the blood quickly coagulates in 

 the syringe. Coagulation can be prevented by drawing up into 

 the syringe before it is used a quantity of 2 per cent, sterile 

 sodium citrate equivalent to the amount of blood it is intended 

 to withdraw. Patients who are seriously ill have often a low 

 blood pressure, and difficulties may be experienced due to the 

 collapsed state of the veins. It is important here that the skin 

 surfaces .should be as little as possible exposed to cold, which 

 still further diminishes the, volume of the superficial circulation. 

 In such cases it may be necessary to expose the vein by 

 dissection. 



In examining the blood of the spleen a portion of the skin 

 over the organ is sterilised in the same way, a few drops are 

 withdrawn from the organ by a sterile hypodermic syringe, and 

 cultures made. (For microscopic methods, vide p. 92.) 



Bacteriological Examination of the Cerebro-spinal Fluid 

 — Lumbar Puncture. — This diagnostic procedure, which is 

 often called for in cases of meningitis, can be carried out with 

 a sterilised " antitoxin needle " as follows : The patient should 

 lie on the right side, with knees somewhat drawn up and left 

 shoulder tilted somewhat forward, so that the back is fully 

 exposed. The skin over the lumbar region is then carefully 



