246 



THE CIRCULATION OF THE BLOOD 



to the zero line and the animal soon dies (Fig. 78). The influence of the 

 third factor is not so great as of the other two, but can be shown by the 

 increased respiratory activity which is likely to develop in the vertical 



Fig. 78. — The effect of gravity on the aortic pressure after division of the spinal cord in the 



upper dorsal region. By placing the animal in the vertical feet-down posture, the pressure fell 



almost to zero, but on returning it to the horizontal posture, the circulation was restored. (From 

 Leonard Hill.) 



tail-down position, the anemic condition of the respiratory center being 

 no doubt the cause of the increased respiration. 



