1889.] The Innervation of the Renal Blood-vessels. 3(57 



The central end of the divided vagus in the rabbit causes a contrac- 

 tion of the kidney, accompanied of course by a rise of blood pressure. 

 In the dog this is also by far the most common result. In the cat, how- 

 ever, and occasionally in the dog, the excitation of this nerve causes a 

 depressor effect, i.e., a fall of blood pressure, and with this fall a 

 passive shrinking of the kidney. The central end of the depressor in 

 the rabbit or of the vagus in the cat causes, as just mentioned, a great 

 fall of blood pressure, .accompanied by a passive contraction of the 

 kidney. Although the blood pressure fall is always a large one, the 

 effect on the kidney volume is but slight. Here again this effect is 

 probably simply the result of the great dilatation of the other abdominal 

 vessels, neutralising, so to say, the renal dilatation, and so causing an 

 actual diminution in the volume of the kidney. In a few cases in the 

 rabbit, where the blood pressure fall has not been very great, an 

 initial slight expansion of the kidney has been detected. 



The stimulation of the central end of a divided posterior root pro- 

 duces in almost all cases a great rise of general blood pressure. This 

 rise is not only large in amount, but it is very sudden, and also of 

 rather short duration. The pressure remains at the maximum height 

 but a few seconds, and when the excitation is over falls towards its 

 normal height ; there is, however, generally a persistent after-effect, 

 that is to say, the pressure remains a little higher than it was pre- 

 viously to the stimulation. There is no very material difference between 

 the results obtained with the lower dorsal nerves and those seen with 

 the upper ones, in both cases a large rise of pressure is obtained ; 

 on the whole, however, the reflex rise seen with the lower 

 nerves is somewhat greater than that obtained with the upper 

 nerves. As a rule the rise of pressure is accompanied by a 

 contraction of the kidney, marked in amount, but not of such a 

 persistent character as that described above as following the excitation 

 of the peripheral end of an anterior root. Frequently the kidney 

 effect is a mixed one, i.e., a contraction followed by an expansion ; 

 not uncommonly, however, there is an initial expansion, the subse- 

 quent course of which is interrupted by a contraction. More fre- 

 quently still no contraction of the kidney is seen, it is replaced by a 

 pure expansion, accompanied as before, however, by a great rise of 

 blood pressure. This effect, however, is most often obtained with the 

 lower dorsal nerves, e.g., the 10th to the 13th. Sometimes when the 

 stimulation of a posterior root gives the renal ex-pansion and rise of 

 blood pressure, the application of the electrodes to the posterior 

 surface of the cord gives an equal rise of blood pressure, accom- 

 panied, however, by contraction of the kidney. Hence the former 

 effect, i.e., the renal expansion, is the result of a more local excitation . 

 When the reflex excitation causes expansion of the kidney there is 

 profuse haemorrhage from the spinal wound. Now this haemorrhage 



