472 BACTERIOLOGY. 



out glass tube g. The receiver and bougie are now heated in an auto- 

 clave to insure sterilization. Finally, the tube e, with the cotton plug- 

 in place, is connected with the pump in the manner indicated in Fig-. 

 66. After filtration, the tube d is disconnected and plugged with 

 sterile cotton taken from an ordinary sterile tube. The tube g is 

 drawn out to a narrow capillary and sealed at the end. In order td 

 remove the liquid from the receiver, the end of the tube g is broken, 

 flamed and inserted into the flask or tube to be filled. 



The bougies, connecting- tubes and receiving" flasks must be per- 

 fectly sterile. The porcelain bougies should be scoured with sand- 

 paper, dried and then sterilized either by the direct heat of a flame, 

 or in a dry heat sterilizer. It is better to sterilize the moist bougie 

 rh an autoclave at 120 for half an hour. The mouth of the bougie 

 should be plugged with cotton and the entire bougie should be wrap- 

 ped in paper. The Berkefeld filters are sterilized by boiling- in water 

 or by steaming- in an autoclave. After filtration, the entire apparatus 

 should be sterilized by steam. 



The receiving- flask (Fig-. 66 e) is connected with a tube (d) filled 

 with sterile sand. This serves to prevent bacteria from entering- the 

 flask when air is admitted through the glass stopcock c. The flask b 

 serves to collect any back-flow that may come from the aspirator. 



Tuberculin. 



Tuberculin contains essentially the soluble products of 

 the tubercle bacillus. The organism growing in a suitable 

 medium gives rise to chemical products, some of which pass 

 out into the surrounding liquid. The bacterial cells are re- 

 moved by filtration and the clear liquid, after concentration, 

 is known as tuberculin. It can be prepared according to 

 the following directions : 



Ordinary bouillon is prepared from beef or veal, and 5 

 per cent, of glycerin is added. This medium is then filled 

 into small Erlenmeyer flasks to a depth of about 1 inch. 

 A broad, low flask provided with a loosely fitting, glass cap 

 is very useful. The flasks should be provided with very 

 firm cotton plugs. The flasks of bouillon are sterilized in 

 steam in the usual way. 



