CH. XXVI.] RELATION BETWEEN QUANTITY AND TENSION 



367 



Suppose that we have six vessels similar to that in fig. 294 

 (Bancroft's Tonometer), and each contains a few c.c. of a solution of 

 haemoglobin and gases of the following composition : 



No. 1. Nitrogen and no oxygen. 



No. 2. Nitrogen and enough oxygen to give 5 mm. oxygen pressure. 



No. 3. ,, ,, 10 ' 



No. 4. 20 



No. 5. 50 



No. 6. ,, ,, 100 



Each tonometer is rotated round and round in a bath at body 

 temperature until the haemoglobin and the oxygen are in equili- 



TQtal Haemoglobin 100 

 ' Percentage Percentage^ 

 of reduced ofOxyhaemo 

 haemoglobin, globm 



' 

 6 

 13 



45 



63 



100 



5 10 20 50 



Oxygen Pressure in mm. of Mercury. 



FIG, 295. Dissociation curve of haemoglobin solution at 37 C. Purple, reduced hemoglobin ; 



red, oxyhiiemoglobin. 



brium; this will take about a quarter of an hour; the solution 

 is then withdrawn and examined in order to ascertain the relative 

 quantities of oxy- and reduced haemoglobin in the six vessels. 



