﻿IX. B, 4 Barber: The Pipette Method 343 



the growth rate of bacteria," the microscope was inclosed in a 

 wooden box which was covered with a cloth jacket lined with 

 asbestos wool. It was warmed by electric coils, and the temper- 

 ature was regulated by a thermoregulator. The adjustment 

 screws of the pipette holder were reached through a small door 

 in one side, the rubber tube was passed out through a small 

 opening at the top, and the mechanical stage was moved by 

 means of rods passing through openings in the top of the box 

 and engaging the screws of the stage. With this apparatus it 

 was possible to keep the moist chamber at a constant temperature 

 throughout an experiment lasting a day or more, A bacterium 

 was isolated, and when it had developed two or four offspring 

 a daughter cell was isolated, placed in a new drop, and so on. 

 Thus a record of the number of generations formed in a given 

 time was kept. The method in which the movements of the 

 pipette are governed by a simple microscope or other holder 

 apart from the compound microscope would be adapted to a warm 

 box too small to admit both microscope and holder. 



DISSECTION 



Some of the simpler dissections in the hanging drop may be 

 done with a single pipette. In order to break apart a clump 

 of bacteria, one may draw away the liquid surrounding the 

 clump and press apart the bacteria with the pipette tip. A 

 yeast cell containing spores may be broken open and the spores 

 separated with the ordinary blunt-pointed pipette. With the 

 pipette drawn to a sharp point (fig. 6), other manipulations 

 are possible. An amoeba, when stretched out on agar, may be 

 cut into two living parts, with little loss of cell contents, by a side 

 stroke with the sharp point. This process is easier if the tip 

 is bent somewhat obliquely as shown in c (fig. 19). The nucleus 

 of an amoeba may be removed by introducing the point close 

 to the nucleus when the latter is at the margin of the animal. 

 A side movement, made with the mechanical stage, removes the 

 nucleus with little loss of protoplasm, and the enucleated amoeba 

 continues its movements. The tip of the dissecting needle may 

 be broken ofif and transformed into a pipette for staining or other 

 purposes. 



I have succeeded in breaking open human red blood corpuscles 

 with a single point, the size of which bore about the same relation 

 to that of the corpuscle as the blunt end of a pencil does to 

 the palm of the hand. 



"Journ. Infect. Dis. (1908), 5, 379. 



