146 



PRACTICAL PHYSIOLOGY 



the blood in the vertical posture is supported by the taut skin, the tone 

 of the skeletal muscles, and the tone of the arterial system. 



FIG. 144. Aortic blood pressure. A, Effect of exciting the central end of vagus. The 

 effect was depressor. B, On shifting up the electrodes to a fresh unexposed part of the 

 nerve the effect changed to pressor. The time is marked in seconds. (L.H.) 



The blood is largely returned to the heart by the action of the skeletal 

 muscles, aided by the valves in the veins, and the respiratory pump. 

 If the spinal cord be divided in the lower cervical region, or the 



FIG. 145. Record of arterial pressure (AP) and plethysun _ 



signal A. The limb expanded in 



ysmogram of lirnb (volume 



record L V\ Excitation of the depressor nerve at signal 

 spite of the fall of arterial pressure. The time is marked in seconds. (Bayliss.) 



administration of chloroform be pushed, these mechanisms are paralysed, 

 and the blood congests in the lower parts, and the heart fails to fill. In 

 such case the circulation is immediately restored by placing the animal 

 in the horizontal posture. 



Asphyxia. The trachea is clamped. Note the sequence of events. 



1st stage : Respirations deeper and more ample; heart accelerated and 



