RESPIRATION 295 



as when fresh coal is placed upon the top of a furnace fire. 

 It does not arise in the living body and its interest in this 

 connection comes from the danger of inhaling it. We may 

 be subjected to its effects when it has reached us from fires 

 or when illuminating gas escapes into our rooms. The com- 

 mon form known as " water gas" contains it in great quan- 

 tity. It is very poisonous and for a simple reason : it de- 

 prives the blood of its oxygen-carrying capacity. 



Carbon monoxid does this by substituting itself for 

 oxygen in the oxyhemoglobin molecule. The unnatural 

 compound formed circulates with little tendency to release 

 the carbon monoxid which is locked in it. (Fortunately, 

 however, it is not absolutely stable. When fresh air has 

 replaced that which brought the foreign, gas into the lungs, 

 the movement of the carbon monoxid molecules is reversed; 

 they now begin to leave the blood.) Just so far as the 

 corpuscles are engaged in carrying this useless gas they 

 are incapacitated for their essential service. If the sub- 

 stitution becomes extensive enough the lack of oxygen is 

 fatal, the heart and the nervous system failing for want of 

 it much as though the victim were bleeding to death. The 

 blood, when saturated with carbon monoxid, has a light 

 color described as cherry red and does not darken on stand- 

 ing as normal blood does. 



Breathing Pure Oxygen. The impression is common 

 that the experience of breathing pure oxygen is a highly 

 exhilarating one. This is not really the case unless an 

 element of suggestion secures the anticipated result. 

 If a man does not know that he has been given the oxygen 

 to breathe he is not likely to report that the experience 

 is at all peculiar. Nevertheless oxygen has often seemed 

 to be of the utmost value in critical pulmonary disease. 

 We must try to reconcile the negative reaction of one 

 who breathes it in health and the marked relief of the 

 pneumonia patient. A simple statement may explain 

 the difference: oxygen does not alter the composition of 

 normal blood in a way that will much affect the organism 

 but it is potent to restore to the standard blood which 

 may have fallen below in illness. 



