48 



PROTOPLASM 



the colony pure, but it represents the progeny of a single 

 parent. To attain this, Schouten in Holland (1899) and 

 Barber in America (1904) devised apparatus to hold and 

 control the movement of needles and pipettes. Schouten's 

 apparatus consists of heavy bars held together by a steel spring. 

 A thumbscrew presses against one bar, separating it from the 

 other. In this manner, movement of the needle is obtained. 

 As Schouten's work involved the isolation of bacteria or Protozoa, 

 he devised a method for catching a microscopic organism within 

 a film of liquid formed by the loop of a fine glass thread when 

 dipped into a solution. 



Fig. 36. — Moist chamber for micromanipulative work. 



The Barber pipette holder in its original design (Fig. 35 

 is a modified form of it) consisted of a support built of three 

 parts, each sliding upon and at right angles to the other, and 

 each controlled by three screws. The instrument was fastened 

 near or directly upon the microscope stage. On its top was a 

 clamp to hold a pipette. The latter projected into a small 

 glass moist chamber where bacteria were suspended in a hanging 

 drop. The three movements, horizontal, lateral, and vertical, 

 which were imparted to the holder, made it possible to bring 

 the pipette into any position in space. 



The isolation of a single bacterium proceeds as follows: 

 A drop of the culture solution containing bacteria is placed 

 on a glass cover slip. The slip is inverted and put into position 

 as the roof of a moist chamber (Fig. 36). A single bacterium 

 is sought through the microscope. The mouth of the micro- 

 pipette is then brought into position directly under the bac- 

 terium and slowly raised until the organism is drawn into the 

 pipette with a small quantity of the solution, either by the 



