SI ri)\ OF THE INFLUKNCK OK OXVCEN ON RADIO-SEXSIl l\l 1 ^■ 



thrsc calculalii)iis, luj\\c'\-cr, was such thai \vc ich il inipoilant to U)' U) 

 measure the pressure difTercntial between the two phases directly. Ordinary 

 polarographic methods were judged to be unsviitable because of the turbu- 

 lence of the Miiid, the nature of the fluid, and the presence of blood. The 

 following procedure was found to give the desired information: 



To the end of a micro gas pipette- a small Perspcx sleeve was attached in 

 such a way as to retain a bubble of about 1 -5 mm diameter formed below 

 the surface of the fluid w hen the pi])ette was introduced at an angle of about 

 45"' to the vertical. The bubble was formed from whatever gas constituted 

 the gas phase in the irradiation vessel. During a period of 5 min below the 

 surface of the tumour suspension, the oxygen content of the bubl^lc changed 



X-rays 



mimiw 



^^w— 



Gas inflow 



^ml. Ascitic fluid 



To flowmeter 

 gas outflow 



wwwww 



Wedge bayonet 

 fitting 



Gas inflow 



Thermojunction 



I I I 1 1 



2 4 



cm 



Figure 1. Perspex irradiation vessel 



to a new equilibrium value corresponding to the actual partial pressure of 

 oxygen in the fluid bathing the tumour cells. The bubble was then with- 

 drawn into the gas pipette and transferred to the analysing compartment 

 of the apparatus shown as a block diagram in Figure 2. This apparatus 

 employs the oxygen analyser described by Hersch-'^. Hydrogen from a 

 cylinder passes through a flowmeter, a catalyst to remove traces of oxygen, 

 an electrolysis cell introduced for calibration purposes, a compartment into 

 which the fluid can be introduced for analysis, and an electro-chemical cell 

 which responds at constant flow rate to the presence of trace amounts of 

 oxygen by giving a current proportional to the concentration of oxygen in 

 the gas phase. In the instrument we have employed, 1 j)art per million 

 (p. p.m.) of oxygen gives a current of the order of 7 [J.A when the hydrogen 



78 



