INNEKVATIUN OF HEART AND BLOOD-VESSELS 573 



time, the passage of nerve impulses through sym- 

 pathetic cells. Painting the ganglia with nicotino 

 has the same effect. In animals the sympathetic 

 cells of which have thus been paralyzed, the stim- 

 ulation of the lumbar nerves in the spinal canal 

 produces no change in the vessels of the genera- 

 tive organs, though in animals not poisoned with 

 nicotine this stimulation causes marked constric- 

 tion. The lumbar vasomotor fibres must there- 

 fore end in connection with sympathetic nerve 

 cells which transmit the constrictor impulse to 

 the blood-vessel. Similar observations in other 

 regions warrant the belief that all the vasomotor 

 fibres emerging from the spinal cord end in like 

 manner. 



Thus the vasoconstrictor system probably con- 

 sists of three neurons. The first is a sympa- 

 thetic cell, lying apart from the central nervous 

 system. Its neuraxon (axis-cylinder process) 

 passes directly to the blood-vessel. The second 

 is a spinal cell, the neuraxon of which leaves the 

 cord and terminates in contact with the sympa- 

 thetic cell or its branches. The third has its 

 cell body in the bulb and its neuraxon termi- 

 nates in contact with the second neuron. 

 Commonly, as for example in the nerves of the 

 extremities, the sympathetic neuraxon passes 

 from the ganglion along the gray ramus into the 



