362 PHYSIOLOGY CHAP. 



vaso-constrictor fibres arise from the anterior roots of the nerves 

 in the median or thoracic section of the cord, which is therefore 

 the principal seat of the apparent origin of these fibres. Next 

 arises the question as to the centres, i.e. the real origins of the 

 same. Other special questions are associated with these. Is 

 there in the central nervous system one single vasomotor centre, 

 or are there several centres ? If several, are they unified in their 

 functions, and associated so as to form one single system, or can 

 they function independently one of another? Are there con- 

 trolling centres of general circulation on which the tone of the 

 whole vascular system depends, and controlling centres of local 

 circulation, on which the vascular tone of this or that organ or 

 tissue depends ? Generally speaking, it must be admitted that we 

 are not yet in a position to give a clear and exhaustive answer 

 to these different questions, particularly to that of the precise 

 localisation of the vascular centres. We must confine ourselves 

 to the more fundamental and better established data, and to 

 drawing from these such conclusions as are legitimate in the 

 present state of our knowledge. 



As early as 1855, shortly after the discovery of the vaso- 

 constrictors, M. Schiff suggested, in view of the effects of 

 transversely dividing the cord at different heights, that these 

 nerves might have their centre in the bulb or medulla oblongata. 

 In 1859 Cl. Bernard observed a considerable fall in blood pressure 

 after division of the cervical cord, but he did not pursue the 

 subject, and von Bezold next took it up in 1863. He found in 

 curarised animals that stimulation of the cervical cord produced 

 such an increase in arterial pressure that it becomes seven times 

 greater than it was immediately after section of the cord. This 

 marked rise of pressure, which was associated with a pronounced 

 acceleration of cardiac rhythm, was referred by him to increased 

 activity of the heart, without taking into consideration the inter- 

 vention of vascular nerves. 



A year after the publication of von Bezold's theory, Ludwig 

 and Thiry showed it to be erroneous, emphasising the fact that 

 during excitation of the cervical cord the small arteries throughout 

 almost the entire body are constricted, which causes the pressor 

 effect. For, on exciting the cervical cord, a maximal rise of aortic 

 pressure is obtained, even after the whole of the cardiac nerves 

 have been divided. The fall after section is therefore the effect 

 of paralytic atony of the vessels; the rise of pressure during 

 excitation is the effect of vascular hypertony ; there must therefore 

 exist in the bulb, i.e. above the divided and excited cord, a vaso- 

 constrictor centre, which exerts a constant tonic action upon all 

 the small arteries. 



Contemporaneously with Ludwig and Thiry, Goltz, by certain 

 experiments on the frog, showed the importance of vascular tone 



