and Laboratory Methods. 



1805 



down part of the glass tube. If gas bubbles have remained in the test tube 

 force them out by lightly striking at the sides of the tube. If during the sub- 

 sequent sterilization so much of the liquid evaporates that the glass tube has 

 become empty, replace the evaporated medium by fresh, sterile medium. The 

 tubes prepared in this way can be stored away indefinitely 

 without becoming contaminated. In order to inoculate 

 remove the stopper, inoculate the medium in the tube, 

 and replace the stopper carefully so that the bouillon 

 rises into the glass tube. 



An ingenious and simple device has been invented by 

 ^rz^-^/ (1901), (Figs. 46 and 47). The apparatus con- 

 sists of a system of glass and rubber tubes standing in an 

 ordinary test tube. (A), (Fig. 46), is a glass tube some- 

 what constricted at each end ; (B), (C), and (E) are short 

 pieces of rubber tubing; glass tube (D) carries in its 

 upper extremity a small cotton plug. The test tube con- 

 tains some culture fluid as indicated in Fig. 46. 



Method. — Arrange the apparatus exactly as shown in 

 Fig. 46. To expel the air from the fluid, boil the culture 

 medium immediately before inoculation over the flame 

 without removing the inner system of tubes. Then cool 

 the apparatus by placing it in cold water and inoculate 

 the liquid medium in the test tube in the usual way. 

 Draw the fluid up into the system of glass and rubber 

 tubes to a level above the rubber tube (C) by suction. 

 Compress rubber tube (E) between the fingers to prevent 

 the down-flow of the fluid, now push downward the system 

 of tubes in such a way as to bend rubber tubes (B) and 



(C) in the manner shown in Fig. 47. If the test tube and the inner tube system 

 are of suitable size the rubber tubes mentioned will remain in this bent position. 

 The fluid in tube (A) is thus contained in a water tight space sealed by the acute 

 angle of the rubber tubes. When it is desirable to transplant some of the 

 culture the tube system is straightened out, this will allow the fluid in them to 

 flow out into the test tube, where it is accessible to the platinum loop in the 

 usual way. 



F. THE FERMENTATION TUBE AND ITS MODIFICATIONS. 



The methods and apparatus belonging to this type deserve special mention- 

 ing owing to their great simplicity and efficiency. 



Previous to the invention of the fermentation tube Pasteur devised an appar- 

 atus (Fig. 48) which operates on a similar principle. It consists of a flask (a) 

 which contains the liquid nutrient medium. Tube (b) is conducted into a porce- 

 lain dish containing the same medium as the flask, tube (c) serves for the pur- 

 pose of introducing the medium and the culture. It carries a glass'turn cock (e) 

 above which it is extended into a short rubber stoppered bulb (f ) which forms 

 the reservoir of the inoculating material. 



Figs. 46 and 47. 



