168 SCIENCE PROGRESS. 



steady fall of the blood pressure within the arterial system. 

 Here we have a very remarkable phenomenon, how is it to 

 be explained ? Well, this nerve is an afferent nerve from 

 the heart, i.e., it conducts impulses from the heart to a part 

 of the central nervous system or bulb, which, when they 

 reach that organ, so modify the activity of the so-called 

 vaso-motor centre situated therein, as to permit of the 

 blood-vessels of the abdomen becoming so dilated that 

 so much blood accumulates within them as to leave 

 onlv a limited amount for the general circulation, and 

 hence the steady fall of the blood pressure. But what is 

 the use of this nerve ? Ludwig suggested that by means of 

 it the resistance offered to the heart, the essential motor- 

 factor in the circulation, was regulated. In other words, 

 when there is too great resistance to the heart, so that it 

 cannot with ease discharge its contents, the terminations of 

 this nerve in the heart are excited and thus lead to a dilata- 

 tion of the abdominal vessels, whereby the resistance in the 

 arteries is diminished. Thus through this nerve the heart 

 — within limits — -can regulate the resistance offered to the 

 blood discharged from it. 



This nerve is "depressor," therefore, because when 

 stimulated it brings about a diminution of the pressure 

 within the systemic arteries. It is, however, also the 

 sensory nerve of the heart, and is, probably, one of the 

 nerves concerned in the excessively painful attacks which 

 characterise "angina pectoris" or breast-pang. At the 

 present time this nerve may have a special interest 

 apart from its physiological significance. Few of our 

 readers will, perhaps, recognise in the co-discoverer of 

 this nerve, and one of the earliest pupils of Ludwig, a man 

 who has played many parts in the world — physiological and 

 political. Cyon, as his career has proved, was what the 

 Germans call a many-sided man. The writer made his 

 acquaintance in Leipzig many years ago, when he was 

 Professor of Physiology in St. Petersburg, and, if he is 

 not mistaken, the M. de Cyon who a few weeks ago was 

 deprived of his rights as a Russian citizen by an Imperial 

 ukase is E. Cyon of depressor nerve fame. Many years 



