196 



A TEXTBOOK OF PHYSIOLOGY 



man is crucified that is to say, immobilized in the erect posture 

 the blood slowly sinks to the most dependent parts, oedema and thirst 

 result, and finally death from cerebral anaemia ensues. In man, 

 standing erect, the heart is situated above its chief reservoir the 

 abdominal veins. The blood is raised by the action of the respiratory 

 movements, which act both as a suction and as a force pump; for the 

 blood is not only aspirated into the right ventricle by the expansion 



rtJBf&fc&iN^^ - ' 



,- . 



FIG. 100. To SHOW EFFECT OF GRAVITY UPON THE CIRCULATION : CAROTID AND 

 SUPERIOR VENA CAVA PRESSURES OF DOG. (L. H.) 



FD, Animal turned into feet-down position with cannulse in axis of rotation. The 

 arterial pressure fell in fifty minutes from 110 mm. Hg to 42 mm. Hg. From C 

 to EX animal was immersed in a bath which was deepened to chin at D. Note 

 increased effect of respiration on venous pressure after FD, and again after bath. 

 Note also fall of pressures at FD, and compensatory rise of arterial pressure, which 

 gradually weakens. 



of the thoracic cavity, but is expressed from the abdomen by the 

 descent of the diaphragm. When a man faints from fear, his muscular 

 system is relaxed and respiration inhibited. The blood, in conse- 

 quence, sinks into the abdomen, the face blanches, and the heart 

 fails to fill. He is resuscitated either by compression of the abdomen 

 or by being placed in a head-down posture. To prevent faintness 

 and drive the blood-stream to his brain and muscles, a soldier tightens 



