1889.] The Tnnervation of the Renal Blood-vessels. 365 



pressure falls to its normal height. Generally the kidney does not 

 quite regain its former volume, in other words, its vessels remain 

 slightly contracted as a more or less permanent after-effect. This effect 

 is so small that it is not accompanied by any appreciable rise of blood 

 pressure. In some cases after the excitation has ceased, the blood 

 pressure falls slowly but slightly below its previous height and then 

 slowly regains its normal level. That is to say, the sudden and 

 great rise of arterial tension is followed by slight, slow, and gradual 

 fall. This fall of blood pressure is accompanied by a slight contrac- 

 tion of the kidney, the volume of the latter following exactly the fall 

 and subsequent rise of blood pressure. This result is only occa- 

 sionally seen when quick rates of excitation are used, but it becomes 

 more frequent when such a rate as five per second is employed. 



It has been seen with most of the nerves, but it is more common with 

 the upper than with the lower dorsal. Its full significance will be 

 alluded to later, but this result is no doubt due to the excitation of 

 vaso-dilator fibres, the kidney effect being a passive one due to 

 changes of blood pressure produced in other organs. 



In a very small proportion of cases a rise of blood pressure is 

 produced as usual, but the kidney effect is a mixed one, i.e., there is 

 first a slight expansion then a marked contraction. In a still smaller 

 number of cases a renal expansion has been observed, generally 

 accompanied by a slight rise of the general blood pressure, but 

 occasionally no such rise has occurred. When the kidney expansion 

 is accompanied by a rise of general arterial tension, it is no doubt due 

 to the kidney vessels being passively dilated owing to active contrac- 

 tion having taken place elsewhere. When, however, the expansion 

 of the kidney is unaccompanied by any rise of pressure, it is difficult 

 to avoid the conclusion that it is due to the excitation of actual vaso- 

 dilator fibres ; however, better evidence than this will be adduced in 

 support of the existence of these nerves. 



II. The Existence and Course of the Vaso-dilator Fibres. 



Hitherto no definite evidence has been adduced in support of the 

 existence of vaso-dilators for the vessels of the kidney. If, however, 

 the llth, 12th, or 13th dorsal nerves be excited by slow rhythmical 

 shocks, i.e., one per second, it will be found that expansion of the 

 kidney occurs unaccompanied by any rise of blood pressure. This 

 renal expansion is marked in character and rather persistent in its 

 duration, that is to say, the organ does not return completely to its 

 original volume after the cessation of the excitation. It is clear that 

 the renal expansion is an active one, since the nerve stimulation has 

 produced no obvious effect on the blood pressure. This striking 

 result is not so easily obtained with the higher nerves ; with these 

 the same excitation produces a fall of blood pressure, accompanied 



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