DRUGS ACTING ON THE URINARY ORGANS 45 



is impossible. This fact is often lost sight of. Water is absorbed from 

 the bowels (hardly at all from the stomach) ^ where it becomes salt solu- 

 tion by taking up sodium chloride from mucus or food, or from super- 

 ficial cells of the tract, or from that formed by the neutralization 

 of HCl from the stomach. Water then enters the blood as an isotonic 

 or hypotonic salt solution, increasing its mass (hydremic plethora) and 

 its pressure, thus dilating the renal arterioles and augmenting the flow 

 of urine. Experimentally, Raphael doubled his urinary output by 

 doubling his intake of water. But the most powerful drug (diuretin) 

 only enhanced his urinary flow 50 per cent. The salts act chiefly upon 

 the glomerules. When hypertonic salt solutions enter the blood they 

 increase its osmotic pressure and water passes into the blood from the 

 tissues. The osmotic, pressure is then lowered, but the mass of blood is 

 increased, together with vascular tension, and thus dilatation of the renal 

 vessels, and diuresis. The most diuretic salts include potassium acetate, 

 citrate, bitartrate, and solution of ammonium acetate. Sodium chloride 

 and sulphate; potassium nitrate, bicarbonate and iodide; and magnesium 

 salts ; may act as diuretics, but not so certainly. Digitalis, squill and 

 strophanthus are powerful diuretics when the circulation is poor, with 

 venous engorgement and low pressure, by overcoming this condition and 

 increasing the flow of blood through the arterioles of the glomerules. 

 They may, like many diuretics, have a local action to dilate arteries in 

 the kidneys and to stimulate renal cells, but this is doubtful. In fact 

 it is probable that powerful diuretics usually act locally to dilate the 

 renal arteries. This has been noted in the case of caffeine (Pearce) 

 but has not been specifically proved in the case of most diuretics. The 

 nitrites are diuretic if they dilate the renal a»terioles more than the arte- 

 rioles generally. 



(2) jDiuretics stimulating the renal cells, or lessening absorption 

 from the tubules, or both. 



The matter of absorption from the tubules is disputed. Some author- 

 ities deny that resorption of water or other substances plays any im- 

 portant part in urinary secretion. Caffeine and theobromine act chiefly 

 through powerful stimulation of the renal cells of the tubules, besides 

 dilating renal vessels through excitation of the heart and augmenting 

 blood pressure. The irritant diuretics contain volatile oils, resins or aro- 

 matics, as buchu, juniper (gin), turpentine and cantharides. They 

 stimulate the renal cells, or hinder resorption, or both. Urea is the 

 natural stimulant of the renal cells. The irritant glucosides, scoparin 

 and asparagin, act as renal stimulants. Calomel either stimulates the 

 renal cells, or causes diuresis indirectly, in' relieving venous engorgement 

 (which obstructs flow in the renal arterioles) by its cathartic action. 

 Diuretics may lessen resorption in the tubules either by hindering the 

 absorbing power of the tubules, or by hastening the flow of urine through 

 them. The solids in the urine are chiefly increased during the first few 

 days after the use of diuretics, and the filtered substancs from the mal- 

 pighian bodies (urea and salts) are eliminated more proportionately by 

 diuretics than the secreted matters (pigment, creatin, uric acid). 



Diuretics, according to Fischer's recent and much discussed theory, 



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