EXCRETION 45 1 



the urine, and there is no doubt that other amino-acids, 

 arising from the decomposition of proteins, are also present 

 in such conditions. 



Sugar. In diabetes mellitus, although the quantity of urine is 

 usually much increased, its specific gravity is above the normal ; and 

 this is due chiefly to the presence of sugar (dextrose), which generally 

 amounts to i to 5 per cent., but may in extreme cases jreach 10 or 

 even 15 per cent., more than half a kilogramme being sometimes 

 given off in twenty-four hours. 



The name of the tests for dextrose is legion. They are mostly 

 founded on its reducing action in alkaline solution. Hydrated oxide 

 of bismuth (Boettcher), salts of gold, platinum and silver, indigo 

 (Mulder), and a host of other substances, are reduced by dextrose, 

 and may be used to show its presence. The reduction of cupric 

 salts (Trommer) , fermentation by yeast, and the formation of crystals 

 of phenyl-glucosazone are the best established tests. (See Practical 

 Exercises, p. 488.) 



Proteins. Serum-albumin and serum-globulin are the proteins 

 most commonly found in pathological urine. Both are coagulated 

 by heating the urine, slightly acidulated if it is not already acid, or 

 by the addition of strong nitric acid in the cold. Proteoses (albu- 

 moses) are also occasionally present, e.g., in the disease called 

 ' osteomalacia ' and in conditions associated with the formation and 

 especially with the decomposition of pus. They may be recognised 

 by the tests given in the Practical Exercises (p. 426). It is doubtful 

 whether the presence of true peptone has as yet been satisfactorily 

 made out. 



The presence of bile-salts may be shown by Hay's test, or Petten- 

 kofer's test (p. 430). 



The pigments of blood and bile may be detected by the char- 

 acters described in treating of these substances ; the spectrum of 

 oxy haemoglobin, or methaemoglobin, or any of the other derivatives 

 of haemoglobin, with the formation of haemin crystals, would afford 

 proof of the presence of the former, and Gmelin's test of the latter. 

 The red blood-corpuscles, seen with the microscope, are the most 

 decisive evidence of the presence of blood, as leucocytes in abundance 

 are of the presence of pus. It should be remembered that pus in 

 the urine of women has sometimes no significance except as showing 

 that there has been an admixture of leucorrheal discharge from the 

 vagina. (See Practical Exercises, pp. 65, 494.) 



The Secretion of the Urine. We have now to consider the 

 mechanism by which the urine is formed in the kidney from the 

 materials brought to it by the blood. And here the same 

 questions arise as have already been discussed in the case of the 

 salivary and other digestive glands : (i) Are the urinary con- 

 stituents, or any of them, present as such in the blood ? (2) If 

 they do exist in the blood, can they be shown to be separated 

 from it by processes mainly physical or mainly ' vital ' in other 

 words, by ordinary nitration, diffusion and osmosis, or by the 

 selective action of living cells ? In the case of the digestive 

 juices it has been seen that some constituents are already present 

 in the blood, but that physical laws alone, so far as we at present 



29 2 



