224 PHYSIOLOGICAL CHEMISTRY. 



blood, the former containing plenty of oxygen in combination 

 while the latter is deficient. The loss of oxygen is illustrated 

 by some simple experiments : 



Ex. Shake about 10 cc. of diluted defibrinated blood with a few drops 

 of ammonium sulphide solution or with Stokes' reagent. (Stokes' reagent 

 is a solution of ferrous sulphate, to which a small amount of tartaric acid 

 has been added, and then ammonia enough to give an alkaline reaction.) 

 Warm gently, and observe that the bright color of arterial blood gives 

 place to the darker purple of venous. On shaking the mixture now with 

 air the bright red color returns. For the success of this experiment where 

 Stokes' reagent is employed it should be freshly prepared before use. Vari- 

 ous other substances behave in similar manner. 



Ex. Generate some hydrogen gas in the usual manner, and allow it to 

 bubble through diluted defibrinated blood. A change of color follows after 

 a time, due to the mechanical loss of oxygen. The same result may be 

 accomplished by exhausting the oxygen of the blood by means of an air 

 pump. Exposure to the air restores the color in a short time, as before. 



The color change may be noticed readily with the unaided 

 eye, but is much more marked when observed in the spectro- 

 scope, as will be pointed out below. 



The maximum amount of oxygen which may be held by 

 the hemoglobin was given above as i molecule for i molecule 

 of the pigment. This holds only for strong oxygen pressure, 

 however. Under lower atmospheric pressure a part of the 

 oxygen becomes dissociated, as illustrated by these figures 

 given by Huefner for a 14 per cent hemoglobin solution : 



The loss of oxygen does not become marked until compara- 

 tively low pressures are reached. 



Carbon Monoxide Hemoglobin. When a current of car- 

 bon monoxide is led into a blood solution it displaces the oxy- 

 gen and forms a very stable compound. One molecule of the 



