54 ADVANCED STUDIES IN PHYSIOLOGY. 



the. frame work or body of the corpuscle, which latter is 

 called the stroma. As haemoglobin is soluble in many 

 liquids it can easily be dissolved out of the corpuscle and 

 the colorless body, or stroma left. Haemoglobin possesses 

 in a remarkable way the ability to unite with oxygen when 

 that gas is plentiful, and to give it up again when the gas 

 is not plentiful. It is this property which gives to it its 

 important function in the body. A large amount of oxygen 

 is required in the body to keep up the relatively high and 

 constant temperature, and to make possible the large 

 expenditures of energy which are necessary to maintain 

 life. The mere liquid plasma of the blood would be per- 

 fectly unable to carry this oxygen in sufficient amounts. 

 While this plasma, like water, which is its main constit- 

 uent, can dissolve a little oxygen we know that fishes 

 derive their oxygen out of the water in which it is dissolved 

 our own experience shows us how limited this supply is, 

 and how constantly water must be renewed in aquaria to 

 make possible the existence of life in it. It is estimated 

 that the haemoglobin carries about nine-tenths of all the 

 oxygen. It is not necessary to call attention to the result 

 that would follow doing away with this haemoglobin and so 

 reducing the oxygen supply ninety per cent. 



The Oxygen -carry ing Property of HcemogloUn. 



The at first puzzling question, why the haemoglobin 

 should unite with the oxygen in the lungs and then give it 

 up in the tissues and not attempt at times to carry the oxy 

 gen from the tissues to the lungs, is easily explained on 

 physical and chemical grounds. Haemoglobin will combine 

 with the oxygen when it is exposed to an atmosphere that 

 has a pressure of at least one-sixth of the normal atmos- 

 pheric pressure. Exposed to an atmosphere less than one- 

 sixth of the normal pressure it not only refuses to unite 

 with oxygen, but actually disunites with the oxygen which 

 it already has and sets it free. Now we know that the 

 atmosphere is composed of about four-fifths of nitrogen and 



