68 METHODS OF CULTIVATION OF BACTERIA 



emulsion and three of diluent had been present in the mixture, 

 and that in the fields examined there were 500 red cells and 

 600 bacteria. It is evident that in the undiluted culture for 

 500 red cells there would have been 2400 bacteria. Now 

 500: 2400:: 5, 000,000: 24,000, 000, which last figure is the 

 number of bacteria per c.mm. of the emulsion. 



The Bacteriological Examination of the Blood. (a) This 

 may be done by taking a small drop from the skin surface, e.g. the 

 lobe of the ear. The part should be thoroughly washed with 

 1-1000 corrosive sublimate and dried with sterile cotton wool. 

 It is then washed with absolute alcohol to remove the antiseptic, 

 drying being allowed to take place by evaporation. A prick is 

 then made with a sterile surgical needle ; the drop of blood is 

 caught with a sterile platinum loop and smeared on the surface 

 of agar or blood serum. Film preparations for microscopic 

 examination may be made at the same time. It is rare to obtain 

 growths from the blood of the human subject by this method 

 (vide special chapters), and if colonies appear the procedure 

 should be repeated to exclude the possibility of accidental con- 

 tamination. 



(b) A larger quantity of blood may be obtained by puncture 

 of a vein ; this is the only satisfactory method, and should be 

 the one followed whenever practicable. The skin over a vein 

 in the forearm or on the dorsum of the foot having been sterilised, 

 the vein is made turgid by pressure, and the needle of a syringe 

 of 10-15 c.c. capacity, carefully sterilised, is then plunged 

 obliquely through the skin into the lumen of the vessel. Several 

 cubic centimetres of blood can thus be withdrawn into the 

 syringe. Some of the blood (e.g. 1 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 C., which is then plated. The flasks, etc., are then 

 incubated. By this method cultures c^h often be obtained where 

 the former method fails, especially in severe conditions such as 

 ulcerative endocarditis, streptococcus infection, etc. Part of the 

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

 then made. 



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 withdrawn from the organ by a sterile hypodermic syringe and 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. 87.) 



Bacteriological Examination of the Cerebro-spinal Fluid 

 Lumbar Puncture. This diagnostic procedure, which is some- 

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



