374: HANDBOOK OF PHYSIOLOGY. 



(1.) The heart's action is amongst the most important. When the 

 cardiac contractions are increased in force, increased diuresis is the re- 

 sult. 



(2.) Since the connection between the general blood-pressure and the 

 nervous system is so close it will be evident that the amount of urine 

 secreted depends greatly upon the influence of the latter. This may be 

 demonstrated experimentally. Thus, division of the spinal cord, by 

 producing general vascular dilatation, causes a great diminution of 

 blood-pressure, and so diminishes the amount of water passed; since the 

 local dilatation in the renal arteries is not sufficient to counteract the 

 general diminution of pressure. Stimulation of the cut cord produces, 

 strangely enough, the same results i. e., a diminution in the amount of 

 the urine passed, but in a different way, viz., by constricting the arte- 

 ries generally, and, among others, the renal arteries ; the diminution of 

 blood-pressure resulting from the local resistance in the renal arteries 

 being more potent to diminish blood-pressure in the glomeruli than the 

 general increase of blood-pressure is to increase it. Section of the 

 renal nerves or of any others which produce local dilatation without 

 greatly diminishing the general blood-pressure will cause an increase in 

 the quantity of fluid passed. 



(3.) The fact that in summer or in hot weather the urine is dimin- 

 ished may be attributed partly to the copious elimination of water by 

 the skin in the form of sweat which occurs in summer, as contrasted 

 with the greatly diminished functional activity of the skin in winter, 

 but also to the dilated condition of the vessels of the skin causing a 

 decrease in the general blood-pressure. Thus we see that in regard to 

 the elimination of water from the system, the skin and kidneys perform 

 similar functions, and are capable to some extent of acting vicariously, 

 one for the other. Their relative activities are inversely proportional to 

 each other. 



The intimate connection between the condition of the kidney and the 

 blood-pressure has been exceedingly well shown by means of an instru- 

 ment called the Oncometer, recently introduced by Koy, which is a 

 modification of the plethysmograph (Fig. 260). By means of this appa- 

 ratus any alteration in the volume of the kidney is communicated to an 

 apparatus (oncograph) capable of recording graphically, with a writing 

 lever, such variations. It has been found that the kidney is extremely 

 sensitive to any alteration in the general blood-pressure, every fall in the 

 general blood-pressure being accompanied by a decrease in the volume 

 of the kidney, and every rise, unless produced by considerable constric- 

 tion of the peripheral vessels, including those of the kidney, being 

 accompanied by a corresponding increase of volume. Increase of vol- 

 ume is followed by an increase in the amount of urine secreted, and 

 decrease of volume by a decrease in the secretion. In addition, how- 



