386 



RESPIRATION AND EXCRETION 



The volume of carbon dioxide given off is always a little less than 

 the volume of oxygen taken in. This seems to show that some oxy- 

 gen unites with some of the chemical elements in the body. 



Changes in the Blood within the Lungs. Blood, after leaving 

 the lungs, is much brighter red than just before entering them. 

 The change in color is due to a taking up of oxygen by the hcemo- 

 globin of the red corpuscle. Changes taking place in blood are 

 obviously the reverse of those which take place in air in the lungs. 

 Blood in the capillaries within the lungs gains from four to five per 

 o \ ^^-3^r-iv-:rr---x I/ cen ^ f oxygen, which the air loses. 

 '*3^^$ '***' f^&&s-'* At the same time blood loses the four 



per cent of carbon dioxide, which the 

 air gains. The water, of which 

 about half a pint is given off daily, 

 is mostly lost from the blood. 



a 



Problem LIII. A study of ven- 

 tilation. (Laboratory Manual, 

 Prob. LIII.) 



Need of Ventilation. During 

 the course of a day the lungs have 

 lost to the surrounding air nearly 

 two pounds of carbon dioxide. This 

 means that about three fifths of a 

 cubic foot is given off from each 

 person during an hour. When we 

 are confined for some time in a room, 

 it becomes necessary to get rid of 

 this carbon dioxide. This can be 

 done only by means of proper ven- 

 tilation. Other materials are passed 

 off from the lungs with carbon di- 

 oxide. It is the presence of these 

 wastes in combination with carbon dioxide that makes breathed 

 air particularly unwholesome. The presence of impurities in the 

 air of a room may easily be determined by its odor. The close 

 smell of a poorly ventilated room is due to organic impurities 

 given off with the carbon dioxide. This, fortunately, gives us an 





Three ways of ventilating a room: 

 i, inlet for air ; o, outlet for air. 

 Which is the best method of ven- 

 tilation ? Explain. 



