the Urine 32 t 



considers that the high blood-pressure in the glomerulus is the 

 propelling force which drives the urine secreted by the tubules 

 through their very long and narrow passage. He proposes to 

 call the glomerulus a ' propulsor,' and points out that the kidney 

 during activity is tense, hard, and distends its capsule to the 

 utmost, which he considers is explained on the basis of the 

 propulsor theory. The importance of a firm inextensible 

 capsule to the kidney has not previously been insisted upon. 



The action of diuretics has been studied in connection with 

 the question of urinary secretion, and the general outcome of 

 the work is that these effect their purpose either by increasing 

 the flow of blood to the kidneys, or by directly stimulating the 

 secretory activity of the cells. 



The function of the cells of the tubules does not end with the 

 removal from the blood of the substances presented to them ; 

 they are also capable of originating material on their own account. 

 Thus the union of glycine with benzoic acid, resulting in the 

 formation of hippuric acid, takes place in the cells of the tubules, 

 and observations have shown that, providing the benzoic acid 

 be presented to it, the kidney is capable of providing the needful 

 glycine. It can hardly be doubted that what is true of glycine 

 and benzoic acid may also be true of other substances, and that 

 transformations may occur in the cells leading to the production 

 of colouring matters, etc., our knowledge of which is at present 

 obscure. 



The Composition of the Urine depends upon the class of animal ; 

 in all herbivora, with certain minor differences, the urinary 

 secretion is much the same : not so with omnivora or carnivora, 

 which possess a distinctive urine, especially the latter. When 

 herbivora live on their own tissues, as during starvation, they 

 become carnivora, and their urine alters completely in character, 

 corresponding now to the urine of flesh-feeders ; the young of 

 herbivora, if still sucking, have a urine possessing much the same 

 characteristics as that of carnivora. But apart from this general 

 statement, it is necessary to point out that in animals of the same 

 class the composition of the urine may vary within very wide 

 limits, depending upon several causes, of which diet is, perhaps, 

 the most important. 

 Urine consists of — 



Water. 



/ Nitrogenous end-products : urea, uric acid, hip- 

 puric acid, kreatin, kreatinine. 

 Organic matter - < Aromatic compounds : benzoic acid, ethereal 

 sulphates of phenol, cresol, etc. 

 (Colouring matter and mucus. 

 ~ . f Sulphates, phosphates and chlorides of sodium, 



a " \ potassium, calcium, and magnesium. 



31 



