20 GENERAL TECHNIC 



The rapidity and force with which the tube is drawn out determine 

 the caliber of the capillary stem. By drawing rapidly a tapering cap- 

 illary tube is obtained; by drawing slowly a larger capillary tube of 

 more uniform caliber is obtained. Of course, the worker cannot take 

 too much time, as the glass hardens quickly. With a little practice 

 this part of the technic is soon mastered. Thorough and uniform heat- 

 ing and careful, steady pulling when the tube is sufficiently plastic are 

 of primary importance. 



When, owing to an error in judgment in heating the tube, it is with- 

 drawn before it is sufficiently plastic and begins to harden, the situa- 

 tion cannot be remedied by drawing out the tube quickly with a jerk. 

 Similarly, when a tube has been partially drawn and hardens it cannot, 

 as a rule, be reheated and drawn out to make a satisfactory pipet. 



FIG. 2. METHOD OF MAKING A SIMPLE CAPILLARY PIPET. 



Shows manner of holding tubing in a flame and drawing into capillary tubes, 

 large portion has been removed from the center. 



6. After drawing out the pipets the hands should be held steady 

 for a few seconds, i. e., until the glass has hardened; otherwise the 

 tubes will bend and be less satisfactory. 



7. Capillary pipets are manipulated with rubber teats, which should 

 be of the best soft vulcanized rubber, and should fit snugly upon the 

 pipet, rendering it air-tight. 



2. Looped Pipets. Looped pipets find their main application in 

 the measurement of the bactericidal power of the blood, after the 

 method of Sir A. Wright. 1 



The essential features of these pipets are: (a) The capillary stem, 

 which serves for measuring and mixing the bacterial emulsion and serum; 

 (6) the portion that serves first as a chamber for the sterile nutrient 

 broth and later as a cultivation chamber for determining whether the 



1 "Technique of the Teat and Capillary Glass Tube," 1912. Constable and 

 Company, London. 



