RESPIRATION AND BLOOD-PRESSURE 163 



tation is extremely doubtful when a person has been submerged 

 as long as five minutes. 



While the phenomena of dyspnea and asphyxia are referable 

 to the lungs, it is not the need of air in these organs, but of O in 

 the tissues, which gives rise to the symptoms. The non-oxygen- 

 ated blood in asphyxia will not circulate through the capillaries 



FIG. 52. The heart in the final stage of asphyxia. 



The letters have the same meaning as in Fig. 51; in addition, p. c. represents the 

 pulmonary capillaries. The right auricle and ventricle, and the pulmonary artery, 

 are fully distended, while the left cavities of the heart and the aorta are nearly 

 empty. (Kirkes after Sir George Johnson.) 



except with the greatest difficulty, and the result is that it accu- 

 mulates in the arterial system, dams back upon and distends the 

 heart, so that this organ is finally paralyzed and ceases to beat. 

 This is the cause of death from asphyxia. 



Effect of Respiration on Blood-Pressure. The lowest 

 blood-pressure is just after the beginning of inspiration, from 

 which time it increases during inspiration to reach its maximum 

 just after the beginning of expiration; it gradually decreases 

 from this time to the minimum just after the beginning of in- 

 spiration. The general effect, then, of inspiration is to increase 



