1 70 Life and Health 



the regularity of respiration is even greater than when we 

 are awake. There is a particular part of the nervous sys- 

 tem that presides over the breathing function. It is situ- 

 ated in that part of the brain called the medulla oblongata 

 and is fancifully called the "vital knot" (sec. 330). It is 

 injury to this respiratory center which usually proves fatal 

 in cases of broken neck. 



From this nerve center there is sent out to the nerves 

 that supply the diaphragm and other muscles of breathing 

 a force which stimulates them to regular contraction. This 

 breathing center is modified by the condition of the blood. 

 It is stimulated by an excess of carbon dioxide in the blood 

 and is quieted by the presence of oxygen. 



Experiment 76. To locate the lungs. Mark out the boundaries of 

 the lungs by "sounding" them ; that is, by percussion, as it is called. 

 This means to put the forefinger of the left hand across the chest or 

 back and to give it a quick, sharp rap with two fingers of the right 

 hand. Note where it sounds hollow or resonant. 



Experiment 77. Borrow a stethoscope and listen to the respiration 

 over the chest. This is known as auscultation. Note the difference 

 of the sounds in inspiration and in expiration. Do not confuse the 

 heart sounds with those of respiration. The respiratory sounds are 

 better heard on the right side. They may be heard fairly well by 

 applying the ear flat to the chest, with only one garment interposed. 



Experiment 78, Get a sheep's lungs, with the windpipe attached. 

 Ask for the heart and lungs all in one mass. Take pains to examine 

 the specimen first and accept only a good one. Parts are apt to 

 be hastily snipped or mangled. Examine the windpipe. Note the 

 horseshoe-shaped rings of cartilage in front, which serve to keep 

 it open. 



Experiment 79. Examine one bronchus, carefully dissecting away 

 the lung tissue with curved scissors. Follow along until small branches 

 of the bronchial tubes are reached. Take time for the dissection and 

 save the specimen in dilute alcohol. Put pieces of the lung tissue 

 in a basin of water and note that they float 



