Appendix I. On methods 



305 



5cm 



The following are the requirements which should be fulfilled for this purpose : 



(1) The point of the tube must reach easily to the bottom 

 of the blood gas bottle. 



(2) The tubing between B and C should hold about 0'12 c.c. 

 of blood. 



(3) At no place must the bore be so great that bubbles of 

 gas become mixed with the blood as the blood passes down. 



(4) At no place must it be so fine that a froth of mercury 

 and blood which sometimes has to be dealt with, will stick in 

 the tube. 



(5) The stronger it is the better. 



The tubing therefore should be 7 cm. in length, B to C, 

 2 cm. from B to Z>, and 5 cm. D to C. The bore should be 

 uniformly To mm. throughout the whole length of the tube. 



The outside diameter of the fine part of the tube should 

 be 4'5 mm. 



For many purposes the tonometer is neither required to 

 deliver a given quantity of blood nor to deliver it into a 

 narrow mouthed bottle. A tube 7 cm. long and 1'5 cm. bore 

 will do, without any constriction. FIG. 146. 



Laboratory method of fillmg tonometers from stock 



gas mixtures. 



The following is a description of the plant which is in the Cambridge Laboratory 

 for this purpose. 



For each gas mixture two Mariotte 

 bottles of a capacity of 15 litres each are 

 connected. It is better not to get the 

 bottles with ground glass bungs, these are 

 liable to break and the bore of the taps 

 is much too narrow to be serviceable. 

 Rubber bungs are quite satisfactory. They 

 should be bored and glass taps inserted 

 which have a bore of 1 cm. in the stopper. 



Into the top of bottle B should be 

 securely fixed with wire a good rubber 

 cork bored to take the glass tube Y which 

 goes to the bottom of the bottle. The 

 cork in the bottle B has another hole ; 

 through this a short glass tube passes 

 which is connected by rubber to a brass 

 tap. This tap connects at right angles to 

 a brass tube W (see endwise in Fig. 147) 

 which we shall call the vacuum main. In 

 the installation at Cambridge there are 

 five such pairs of bottles, each forming a 

 gas holder, joined to the vacuum main. 



B. R. F. 20 



FIG. 147. 



