CIRCULATION OF BLOOD AND LYMPH. 



of the trunk and extremities pass from the ganglion to the cor- 

 responding spinal nerve by way of the ramus communicans (gray 

 ramus) and after reaching the spinal nerve they are distributed with 

 it to its corresponding region (Fig. 251). In the general region 



Fig. 252. Vasomotor effect of stimulation of the splanchnic nerve peripheral end 

 in the dog (Dawson) : 1. The line of zero pressure; 2, the line of the stimulating pen; on 

 and off mark the beginning and end of the stimulation; 3, the time record in seconds; 4, 

 the blood-pressure record (stimulation causes a marked rise of blood-pressure due to stimu- 

 lation of vasoconstrictor fibers) ; 5, plethysmographic tracing of the volume of the kidney 

 (oncometer) ; stimulation of the splanchnic causes a diminution in volume of the kidney 

 owing to the constriction of its arterioles. 



under consideration (lower cervical to upper lumbar) each ramus 

 communicans between a spinal nerve and a sympathetic ganglion 

 consists, therefore, of two parts, one (white ramus) of preganglionic 

 fibers passing from the spinal nerve to the ganglion, the other 

 (gray ramus) of postganglionic fibers coming from the ganglion to 

 the spinal nerve for distribution to the peripheral tissues. It should 

 be borne in mind that the fibers in the white ramus do not 

 return to the spinal nerve by the gray portion of the same ramus, 



