SECRETION. 461 



Kochelle salt has been added. The latter holds the cupric hydrate 

 in solution. The presence of sugar is denoted by the reduction on 

 boiling of yellow precipitate of cuprous oxide. 



Phenylhydrazin Test. This is, perhaps, the most trustworthy 

 of all the sugar tests. It depends upon the formation of a very 

 characteristic body from phenylhydrazin hydrochloride and sodium 

 acetate: phenylglucosazone. The resultant body is found as yellow 

 crystals, for the most part arranged in rosettes and clusters. They 

 are only sparingly soluble in water. The characteristic crystals are 

 readily detected under the microscope. 



The phenylhydrazin test takes place with glucose, laevulose, and 

 glycuronic acid. 



Fermentation Test for Sugar. With an Einhorn saccharometer 

 tube introduce a definite quantity of urine and a piece of Fleisch- 

 man's yeast about the size of a pea; then stand in a warm place. 

 Next morning read off the percentage of glucose on the instrument. 

 The fermentation test of glucose excludes glycuronic acid, as it will 

 not ferment. 



BILE and BLOOD in the urine have been previously discussed. 



TUBE-CASTS. Cylinders, or casts, of the uriniferous tubules are 

 of prime importance to the physician in his diagnosis of some forms 

 of renal disease. Those which are straight may be said to be casts 

 of the collecting tubes; the more curved and twisted ones are prob- 

 ably from the convoluted tubules. Various kinds of casts, or cylin- 

 ders, are distinguished. 



Theory of the Urinary Secretion. 



The theory of the urinary secretion is summed up by regarding 

 the water (which determines the quantity of the urine) and its salts 

 as a product of filtration from the renal glomerules; the dissolved 

 components (as urea, uric acid, etc.) as products of the special 

 activity of the elements of the epithelium of the contorted tubules. 



That the passage of the water takes place chiefly by filtration 

 is shown by the fact that the quickness of this passage is kept in 

 direct relation with the pressure of the blood in the renal arteries, 

 and the glomerules in particular, from whose vessels the watery ele- 

 ment of the urine is chiefly derived. 



Nevertheless, hydrostatic pressure is not the only factor at 

 work in the glomerules, for their epithelium exerts both a positive 

 and negative influence: positive in that some of the salts of the 



