136 EXPERIMENTAL PHYSIOLOGY. 



position above the bottle. The screw clip 2 is opened so that the 

 air enters the tonometer, the clip 1 is then cautionsly loosened to 

 let a drop or two of blood flow out from the tip of the glass tube,* 

 and after closing it again the end of the tube is wiped free of blood 

 and placed in the bottle so that it dips under the ammonia solution. 

 Clip 1 is now cautiously opened and about 1 c.c. of blood allowed to 

 flow under the ammonia water. If this is done carefully the blood 

 does not mix with the ammonia water but this floats on the top as a 

 layer and so prevents any diffusion of oxygen between the blood 

 and the air. The bottle is firmly closed by its stopper, the stopcock 

 being meanwhile open to the outside so that the level of the clove oil 

 in the manometer is not disturbed. The bottle must then be sub- 

 merged in a water-bath containing water at about room tempera- 

 ture, in which it is left until, with the stopcock closed, no further 

 contraction of volume, due to cooling, is observed to occur. 



The manometer is now removed from the bath and vigorously 

 shaken so that the blood becomes laked and absorbs C>2 from the 

 atmosphere of the bottle. On replacing the bottle in the bath and 

 allowing time for cooling the difference between the levels of clove 

 oil in the two limbs of the manometer is noted. With the stopcock 

 open to the outside, the stopper is removed from the bottle and 

 about 0.25 c.c. of a freshly prepared saturated solution of potassium 

 ferricyanide is placed in the glass spoon suspended from the stopper 

 without allowing any of the ferricyanide to mix with the laked 

 blood. After reinserting the stopper and cooling, the bottle is 

 again removed from the bath and shaken so that the ferricyanide, 

 by mixing with the laked blood, drives off the loosely combined 

 oxygen and raises the pressure, which is measured by the mano- 

 meter. 



The relative amounts of reduced haemoglobin and oxyhaemo- 

 globin present in the blood are proportional to the first and second 

 readings of the manometer; when all is reduced haemoglobin the 

 diminished pressure (shrinkage) recorded in the first shaking of the 

 bottle is the same as the increased pressure recorded in the second. 



*Enough blood should be run out to bring the meniscus of blood in the tono- 

 meter to the upper file mark. 



