4 I2 RESPIRATION 



are at the zero marks and the burette level is at a convenient distance 

 below zero. The gauges are then carefully observed, and the water in 

 the bath is occasionally stirred by blowing air through it. It will be 

 found that when both the gauges are exactly adjusted they do not keep 

 even when left to themselves until at least ten minutes after the blood 

 flask has been placed in the bath. The alterations are compensated by 

 means of the leveling tubes; and when the gauges have come steady, 

 or only move together, the burette is read off exactly. The confining 

 liquid is distilled water containing a small quantity of bile-salts which 

 make the readings more certain and sensitive. 



The blood flask is now agitated for two or three minutes in order 

 that the blood may take up all the gas it is capable of taking. At the 

 same time it is laked by the saponin. In the process of agitation the flask 

 is never removed from the bath. It is held by the neck with forceps or 

 something else interposed to shield it from the warmth of the fingers. 

 The gauges are now again adjusted, and, after they are quite steady, 

 which should be the case almost at once, the burette is again read off. The 

 difference between the two readings gives the gas absorbed by the blood 

 from the air. From this we can calculate the volume of oxygen absorbed 

 by the haemoglobin. 



The first step in the calculation is to reduce the gas absorbed to its 

 dry volume at o and 760 mm. and calculate its volume per 100 cc. of 

 blood. For this purpose the barometer is read and the temperature given 

 by a thermometer (not shown in the figure) fixed on the front of the 

 stand, with the bulb close to the upper part of the burette. It is evident 

 that what is required is not the temperature of the bath or connections, 

 but that of the burette. The reduction is easily made with the help of a 

 table with factors for correction, such as that at page 60 (second edi- 

 tion) of my book on Methods of Air Analysis. 



We have now to calculate how much of the gas absorbed has simply 

 gone into physical solution. Blood in the living body is saturated with 

 nitrogen at the partial pressure of the nitrogen in the alveolar air. 

 Allowing for the aqueous vapor present, this partial pressure is about 

 75 per cent of the existing atmospheric pressure. The coefficient of ab- 

 sorption of nitrogen in blood at 38C is .on, according to Bohr's de- 

 termination. Hence at ordinary atmospheric pressure there will be .83 cc. 

 of nitrogen (at o and 760 mm.) in solution in 100 cc. of blood. The 

 blood in the flask will become saturated at about 15 with nitrogen at a 

 partial pressure of about 78 per cent of an atmosphere ; and, as the co- 

 efficient of absorption is .016, about 1.25 cc. of nitrogen will be in 

 solution per 100 cc. of blood saturated with air at 15. Thus 100 cc. of 

 blood will take up .42 cc. of extra nitrogen on saturation. 



