512 MATERIA MEDIC A AND THERAPEUTICS. 



activity of the renal epithelium, i.e. the excretion of solids and 

 of a certain amount of the water, may be modified by in- 

 fluences of two classes : 



(a) By measures and conditions which affect the renal cells through 

 the composition of the blood in general. Of these, the state of 

 digestion, including the selection of food, is the most important. 

 The quantity of food ; its richness in proteids, carbohydrates, 

 and salts of different kinds ; the relative amount of work thrown 

 upon gastric or acid, and duodenal or alkaline digestion ; and 

 the vigour of hepatic metabolism, as determined by so many 

 causes, including exercise, oxygenation, and the use of drugs- 

 may all be made use of by the pharmacologist in altering the 

 composition of the urinary solids. 



One of the most easy and important of these alterations is 

 in the chemical reaction of the urine. The natural acidity of the 

 urine can be increased by excess of proteids, sugar, and starch, 

 by deficiency of water, by certain wines and spirits, by 

 Salicylic and Benzoic Acids, and by an excess of Tartaric 

 and Citric Acids. The mineral acids have an insignificant 

 or even negative power on the acidity of the urine, a fact 

 which is to be carefully noted. Sulphuric Acid is excreted by the 

 kidneys (in part), but as neutral sulphates; Hydrochloric Acid 

 as neutral chlorides, Phosphoric Acid as phosphates ; Nitric 

 Acid is believed to increase the ammonia in the urine by decom- 

 position in the blood, so that it may have an alkaline influence ; 

 and Tartaric, Citric, and Acetic Acids in combination with 

 Alkaline bases, escape as Alkaline Carbonates. 



On the other hand, we possess abundant and powerful means 

 of rendering the urine alkaline. Amongst foods, the most effective 

 in this direction are fruits, milk, and fish, as they throw into the 

 blood a quantity of Alkaline Citrates,Tartrates, Acetates, Carbon- 

 ates, and Phosphates, which are directly or indirectly excreted by 

 the kidneys. Amongst drugs, the whole group of Alkalies and 

 Alkaline Earths have an alkalinising effect on the urine, excepting 

 Ammonia, which is completely broken up in the system. Thus 

 the alkalies are entirely unlike the mineral acids in exercising 

 a powerful and available influence on the reaction of the urine. 



(b) By measures which affect the renal epithelium specifically. 

 Whatever may be their alkalinising value in the blood, certain 

 substances have a special influence on the urine by specifically 

 acting upon the renal cells. Thus Potash and Soda possess 

 equal values as alkalinisers of the blood, but potash will much 

 more powerfully and quickly neutralise the acidity of the urine, 

 because whilst Soda is excreted partly by the bile and bronchial 

 mucus, or locked up in the system as the neutral chloride 

 of sodium, Potash stimulates the renal epithelium, which 



