660 THE SECRETION OF URINE, 



tubules of the kidney suggests that in this organ, as in the salivary 

 glands, the secretion of urine may be under the direct control of the 

 central nervous system, apart from any influence that this system may 

 have on the renal circulation. We have already seen that the urinary 

 secretion is extremely susceptible to variations in the pressure and 

 velocity of the blood in the renal vessels, and also that these latter are 

 under the direct control of the nervous system by means of vasodilator 

 and vaso -constrictor nerve fibres. 



Various authorities have described experiments which should 

 demonstrate the existence of secreto-motor nerves to the kidney. Thus, 

 in 1835, Claude Bernard 1 showed that in some cases, where puncture of 

 the medulla was carried out with the* view of producing diabetes, the 

 result was an increased flow of urine, containing no sugar, i.e. diabetes 

 insipidus. These experiments were repeated in much greater detail by 

 Eckhard, 2 who showed that, in the rabbit, polyuria might be caused, not 

 only by a puncture of the medulla, but also by chemical or mechanical 

 stimulation of the neighbouring portion of the superior vermis of the 

 cerebellum, especially if, previously to the operation, the nerves going 

 to the liver had been divided. Moreover, it is a familiar fact to 

 clinicians, that injuries to the head, epileptic attacks, and especially 

 lesions in the neighbourhood of the medulla, may bring about a condi- 

 tion of diabetes insipidus. 



We know already that division of one splanchnic nerve will cause 

 an increased secretion of urine in the kidney of the same side, and it is 

 natural to imagine that the mechanism of the increased urinary sec- 

 tion after the piqtire is of the same nature. Eckhard pointed out, how- 

 ever, that the course of events is different in the two cases. After division 

 of one splanchnic, the flow of urine is almost immediately somewhat 

 increased, and this moderate increase lasts a considerable time (three to 

 four hours at least). The first result of puncture of the medulla is a 

 cessation of the urinary flow. This is followed shortly by an increase 

 much greater than is caused by section of the splanchnic, but only 

 lasting one to two hours. Moreover, the effect of the diabetic puncture 

 is observable even after section of the splanchnics, as well as of all the 

 nerves which may possibly send branches to the kidney. Eckhard con- 

 cludes, therefore, that the effect must be due to one of two causes : 

 either an increased general blood pressure, in consequence of the 

 stimulus caused by the puncture, or the excitation of nerve fibres which 

 run in the walls of the renal artery itself. The first explanation must 

 be rejected, since direct measurement of the blood pressure does not 

 show any definite rise in consequence of the puncture. We must there- 

 fore accept the second explanation as the correct one. Eckhard regards 

 these nerve fibres as secreto-motor, and believes that the urinary secre- 

 tion is under the control of a nerve centre, situated most probably in 

 the medulla. He bases this hypothesis on the facts that section of the 

 cord below the medulla stops the flow of urine, and that stimulation of 

 the cut cord does not bring back the flow, in spite of the rise of blood 

 pressure which is induced. We know now, however, that the negative 

 result of stimulating the cut cord is due to the constriction of the renal 

 vessels, which occurs together with those of other parts of the body, so 



1 "Le9ons de pliysiol.," 1835, tome i. p. 339. 



2 Beitr. z. Anat. u. PhysioL (Eckhard}, Giessen, 1869, Bd. iv. S. 1-32 and 153-193 ; 

 1870, Bd. v. S. 147-178 ; 1872, Bd. vi. S. 1-18 and 51-94. 



