72 METHODS OF CULTIVATION OF BACTERIA 



three more times, and finally the tip of the tube beyond 

 the lowest mark is broken off. Thus on the capillary part 

 of the pipette we have five divisions, each capable of 

 holding 5 c.mm. of fluid. The rest of the pipette is now 

 calibrated so as to determine that part capable of containing 

 225 c.mm. and 250 c.mm. This is done by placing a rubber 

 nipple on the wide end of the pipette and sucking up some 

 water tinted with, say, methylene-blue till the 25 c.mm. mark 

 is reached ; a small air-bubble is then allowed to enter the 

 pipette, then other 25 c.mm. of fluid, then another bubble, and 

 so on till nine volumes each of 25 c.mm. have been sucked up. 

 A mark is then made on the tube at the upper level of this 

 amount, other 25 c.mm. are sucked up, and another mark made. 

 The fluid is expelled, the tube dried, and that part containing 

 the 225 and 250 marks is drawn out into an almost capillary 

 diameter, the manipulation by which the marks were originally 

 arrived at is repeated, and thus in the new marks made a more 

 accurate calibration for these amounts is attained. In order to 

 form a safety chamber a second bulb is formed by drawing out 

 the tube a little higher up, as in the figure, and finally the upper 

 inch or two are bent at right angles to the calibrated limb. In 

 doing this a loop may be thrown on the plastic melted capillary 

 tube exactly in the way in which a similar loop may be thrown 

 on a piece of cord. With such a pipette any required dilution 

 of a culture can be made on the principles already described. 



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 micro- 

 scopic 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 pro- 

 cedure should be repeated to exclude the possibility of accidental 

 contamination. 



(b) A larger 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, 

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



