92 CLINICAL DIAGNOSTICS. 



A pathological increase in the number of respiratory 

 movements is spoken of as dyspnea (see this). A decrease in 

 the number of respiratory movements is rarely observed. It is 

 seen in severe brain affections (hemorrhage, hydrocephalus, 

 tumors, poisonings, action of septic substances during the 

 course of pulmonary gangrene), also where the anterior air 

 passages are occluded (stenosis), which is combined with a 

 pronounced inspiratory tone. 



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 dihi- 

 tation of the thorax. When the organ 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 drcmnng 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. 



The normal rhythm of the respirations can be pathologic- 

 ally altered in that : 



1. The inspiratory movement lasts too long, 

 the free entrance of air being prevented by stenosis of the 

 respiratory passages. 



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

 ation of the diaphragm not sufficing to a complete expiratory 

 movement. 



As the respirations are in a measure controllable by the 

 will, which depends upon the cerebrum, excitement or inflam- 

 matory conditions occasioning either brain irritation or depres- 

 sion, at times can bring about marked change in the rhythm 



