RESPIRATORY APPARATUS. 97 



A pathological increase in the number of respiratory 

 movements (polypnea) is spoken of as dyspnea (see this). 



A decrease in the number of respiratory movements 

 (oligopnea) is rarely observed. It is seen in severe brain af- 

 fections (hemorrhage, hydrocephalus, tumors, poisonings, ac- 

 tion of septic substances as in pulmonary gangrene), also 

 where the anterior air passages are occluded (stenosis), which 

 is combined with a pronounced inspiratory tone. Oligopnea 

 associated with respiratory noise is always a sign of severe 

 illness. 



b. Physiology of respiration. When an animal is at 

 perfect rest, the respirations are produced by the action of the 

 diaphragm. The contraction of the diaphragm produces a dila- 

 tion of the thorax. When the muscle contracts it flattens and is 

 drawn backwardly, the false ribs becoming elevated. Notwith- 

 standing that the diaphragm is stretched 

 transversely between the thoracic and ab- 

 dominal cavities, its contraction does not 

 cause its points, of insertion to approach 

 each other, for the reason that the intestines keep it con- 

 tinually forward, which produces a drawing anteriorly of the ribs 

 rather than to cause them to approach the median line. O n 

 account of the double articulation of the 

 ribs with the dorsal vertebrae the forward 

 movement of them is accompanied by a rota- 

 tion. The diaphragm dilates the thorax in that it draws the ribs 

 forward and rotates them outward at the same time. 



The expiration follows the relaxation of the diaphragm, 

 which takes place immediately after the inspiration. The dura- 

 tion of expiration is longer than that of inspiration; between 

 them in quietly breathing animals there is a short pause. 



1. The normal rhythm of the respirations can be patho- 

 logically altered in that : 



The inspiratory movement lasts too long, 

 the free entrance of air, being prevented by stenosis of 'the- 

 respiratory passages (inspiratory dyspnea). 



2. The expiratory act lasts too long, the re- 

 laxation of the diaphragm not sufficing to a complete expira- 

 tory movement (expiratory dyspnea). . :.■ 



As the respirations are in a measure .controllable, by the 

 will, which depends upon the cerebrum, excitement oijnflam- 



