188 RESPIRATION 



ber died. On board a steamship, during a stormy night, one 

 hundred and fifty passengers were confined in a small cabin, 

 but when morning came, only eighty remained alive. 



19. Changes in the Blood from Respiration. The most strik- 

 ing change which the blood undergoes by its passage through 

 the lungs, is the change of color from a dark blue to a bright 

 red. That this .change is dependent upon respiration has been 

 fully proved by experiment. If the trachea, or windpipe, of a 

 living animal be so compressed as to exclude the air from the 

 lungs, the blood in the arteries will gradually grow darker, 

 until its color is the same as that of the venous blood. When 

 the pressure is removed, the blood speedily resumes its bright 

 hue. Again, if an animal breathes an atmosphere containing 

 more oxygen than atmospheric air, the color changes from 

 scarlet to vermilion, and becomes even brighter than arterial 

 blood. This change of color is not of itself a very important 

 matter, but it indicates a most important change of com- 

 position. (See Note 4.) 



20. The air, as we h2,ve seen, by respiration loses oxygen 

 and gains carbonic acid gas ; the blood, on the contrary, gains 

 oxygen and loses carbonic acid gas. Oxygen is the food of the 

 blood corpuscles ; while the articles we eat and drink go more 

 directly to the plasma of the blood. The air, then, it is plain, 



4. Experiment. Changes in the Color of the Blood. The changes 

 produced in the blood by the atmosphere are of easy demonstration 

 before a class. Obtain from a butcher, some freshly "whipped" blood, 

 i.e., blood rapidly stirred with a bundle of twigs while it is being drawn 

 from the animal. This removes all the fibrin, and the blood no longer 

 coagulates. Upon standing, this gradually assumes a dark-brown color. 



To show that the atmosphere, or rather the oxygen in the atmosphere, 

 produces the bright red or arterial blood, fill a pint bottle of white glass 

 about one-third full with this dark blood, and shake it briskly ; it will 

 very promptly assume a brighter color. The same, or a rather better 

 result may be obtained by blowing air through the blood by means of a 

 glass tube inserted into the bottle nearly to the bottom. After having 

 blown air through for a few minutes, the blood assumes a bright scarlet 

 color. Upon standing it again gradually grows dark. 



19. Change in the blood from blue to red. Upon what does the change depend ? How 

 shown ? 



20. What does the air lose and gain by respiration ? What, the blood ? Air as food ? 



