248 THE RESPIRATORY APPARATUS 



separating the capillaries from the intrapulmonary 

 air, the carbon dioxide is given off and the oxygen is 

 taken up and combines chemically with the hemo- 

 globin contained in the red cells, forming oxyhemo- 

 globin, the blood in the arterial capillaries of the 

 pulmonary veins immediately turns bright red as a 

 result of the interchange. This bright red or arterial 

 blood is carried to the tissues by the arteries and 

 capillaries. 



FIG. 94 



Al R 



THIN MUCOSA 



CAP.LLARY BLOOD VESSEL (j)0Q(o) Q QQ><3) 000 <S0 



Diagram of the essentials of a respiratory apparatus. (F. H. G.) 



This power possessed by the blood of absorbing 

 and giving up oxygen and carbon dioxide through the 

 capillary walls from and to the air and tissues respec- 

 tively is based on the well-known fact that liquids 

 will absorb or dissolve at any constant pressure 

 unequal volumes of different gases in accordance with 

 their solubilities, and with variations in temperature 

 (Brubaker) . 



The Relation of the Nerve System to Respiration. 

 The rhythmic movements of respiration are controlled 

 by nerve impulses which arise in groups of nerve cells 

 in the central nerve system, and are transmitted to 

 the inspiratory and expiratory centres in the medulla 

 oblongata, which are stimulated into activity. 



The inspiratory and expiratory centres are included 

 under the term respiratory centre. 



The vagus nerve is the important nerve which 

 transmits nerve impulses from the inspiratory centre 

 in the medulla to the lungs. It contains excitor and 

 inhibitor fibers; the former, when stimulated, increase 

 the rate of inspiration and the latter decrease it. 



