THE EFFECTS OF EXCESS OF CARBON DIOXIDE 307 



Joiiged; the heart-beat is increased in force and frequency; the blood- 

 pressure rises; the tongue in the case of an animal, the lips and face 

 also in the case of man, darken to a purplish hue. 



In the second stage, the respiration becomes violent and con- 

 vulsive; the blood-pressure remains high, due to the vaso-constriction 

 produced; the heart-beats show the sign of vagus inhibition; the 

 duskiness of the mucous membranes increases. 



In the third stage, the breathing and convulsions practically 

 cease; the heart beats feebly and irregularly; the blood-pressure 

 gradually falls, and the tracing shows marked undulations of pressure, 

 known as the Traube-Hering waves (Fig. 108). The pupils become 



Tap 



Lens 



Arc -light 



Microscope 



Frog 



Screen 



Compressed air 

 cylinder 



FIG. 173. DIAGRAM OF APPARATUS BY WHICH EFFECT OF COMPRESSION AND 

 DECOMPRESSION is STJDIED UPON CAPILLARIES OF FROG'S WEB. 



dilated, the mucous membranes become pale and anaemic, faeces and 

 urine may be voided. Post mortem, the right side of the heart is 

 found distended with blood, the left side contracted and empty. The 

 great veins and the lungs are also engorged with blood. 



Effects of Diminished Atmospheric Pressure. Another train of 

 symptoms due to oxygen- want is that known as " mountain or alti- 

 tude sickness." It effects aeronauts as well as mountain-climbers. 

 In their case, the oxygen-want results from the di mi n shed atmo- 

 spheric pressure, and consequent reduction in the partial pressure of 

 the oxygen in the blood. The symptoms are headache, nausea, 

 distress in breathing, especially upon exertion. Mountain sickness 

 frequently begins at altitudes of 6,000 to 10,000 feet, particularly 



