THE KIDNEY. 509 



CHAPTER XIII. 



' THE KIDNEY. 



THE position which the kidney occupies in the circle of the 

 great physiological systems gives a special character to its 

 diseases, and to the actions and uses of remedies in connection 

 with it. The series of vital processes which commences 

 with the admission of food, air, and medicines, ends chiefly 

 with the excretion of urine. Digestion, assimilation, sanguifi- 

 cation, metabolism, circulation, and respiration, all, therefore, 

 affect the activity of the kidney. This is chiefly due to the 

 fact that the kidney does not itself form the urea, uric acid, 

 pigments, salts, and water which form the hulk of the urine 

 that these bodies reach it by the blood, and it has but to sweep 

 them from the circulation. This dependent position of the 

 kidney is of great interest to the practical therapeutist. Clini- 

 cally, the condition of the urine is a key to the manner in which 

 the various viscera are discharging their functions ; pathologi- 

 cally, we often find in other organs the cause of renal disease ; 

 and pharmacologically, we discover that if we wish to affect the 

 composition of the urine and the activity of the kidney, we 

 must, in many cases, direct our measures to the digestive 

 organs, the heart and the vessels. 



Conversely, the kidney makes its influence felt back- 

 wards upon the other organs. Disturbance of the renal 

 function quickly tells upon the blood and viscera. We saw 

 this under the heads of the liver and metabolism, and noted 

 how quickly the retention of waste products checked func- 

 tional activity, like ashes choking out a fire. As striking 

 a relation exists between the kidney and the organs of 

 circulation. Thus the practitioner, adopting the inverse order 

 of investigation, estimates the condition of the kidney by the 

 pulse, bowels, and appetite ; the pathologist finds in the enlarged 

 heart and ruptured vessels of the brain the outcome of disease 

 of the renal glomeruli ; and the pharmacologist relieves the 

 blood pressure or the liver by measures directed to the kidneys. 

 These preliminary considerations will prepare us for the 

 systematic discussion of this complex subject. 



I. PHYSIOLOGICAL RELATIONS. 



The source of the urine is believed to be certainly double. 

 The bulk of the water is excreted in the Malpighian bodies, 

 being squeezed from the glomerulus into the capsule by the 

 blood pressure within the former. The excreting force is 

 determined (1) by the pressure of the blood entering the 



