5. TEMPERATURE CONTROL 0? MOIST ?H.\MBER. 



18 



/f// 



w 



Pig. 13 



Hecker has devised a jacket, heated by electricity, which can be placed around 

 the moist chamber and hence maintain within it any constant temperature. The 

 jacket is made by coiling wire about a frame which surrounds the chamber on 

 three sides. The terminals of the wire are connected to a rheostat by which the 

 amount of heat may be controlled. The construction of the device is indicated 

 in Figure 1?., where (w) is the wi.-e fastened about the internal frame, and (7) 

 the terminals leading to the rheostat. Hecker, 1916. 



TRANSFER OF BAOT^IA. 



Kahn has applied the micromanipulative technique to the isolation of single 

 bacteria. His method, now generally in use in bacteriological laboratories, is 

 as follows. Micropipettes are drawn on the ends of 4 mm ©4 1 glass tubing cut into 

 six inch lengths. It is more convenient to have the moist chamber with its open 

 end so placed that the pipette may project into it from the left side. This 

 facilitates the frequent interchange of pipettes so necessary in isolating bac- 

 teria. For this purpose the pipette holder is attached to the left side of the 

 microscope. A deeper and wider moist chamber than that used by Chambers for his 

 cytological work is found more convenient for rapid changes. The method of pro- 

 cedure for the isolation of a single bacterium may he summarized as follows: 



(1) Prepare a young liquid culture from a subculture not more than 18 hours old. 



(2) Insert the tip of a sealed pipette into a tube of liquid culture and open it 

 by gently rubbing it against the wall of the tube. Then with a rubber tube on its 

 shank suck up a small amount of the' culture. (3) Mount this on the instrument and 

 bring the tip into focus in the center 6f the microscopic field. Raise the pipette 

 until its tip touches the undersurface of the coverslip and expel an appreciable 

 droplet. This may have to be diluted with sterile fluid if the culture is too 

 dense. (4) After securing a moderately dilute preparation fill the same or a new 

 pipette to a little below its bend. Lower the pipette, and with the aid of the 

 mechanical stage, bring another portion of the cover slip into view. By alter- 

 nately raising and lowering the pipette a series of minute droplets will be found 

 to contain a single microorganism. (5) Replace this pipette with a new sterile 



one containing a small amount of sterile liquid medium which must not run Vlow 

 the elbow. This new pipette is now brought directly under a droplet containing a 

 single microorganism. The pipette is then slowly raised and as soon as it touches 

 the surface the droplet with the contained organism will flow into it. This occurs 

 by capillary attraction and no suction is required. (6) This droplet, which is 

 known to contain only one microorganism, is carefully removed from the apparatus 



