EXCRETION OF WASTE PRODUCTS 183 



spite of the neutralisation of the acids by ammonia certain 

 amounts of the fixed bases, sodium and potassium are removed 

 by combination with the acids. There is thus a danger of 

 coma and death from acid poisoning. Administration of 

 alkaline salts of sodium and potassium is useful in these 

 conditions. 



Ammonia can be estimated in two ways. In the first way 

 the solution is neutralised to phenol phthalein and formal- 

 dehyde is added. This condenses with ammonia to form liexa- 

 methylene tetramine, which is neutral, hence an amount 

 of acid equivalent to the ammonia is liberated. By measuring 

 the amount of alkali necessary to neutralise the solution once 

 more the amount of- ammonia is given.* This method gives 

 slightly too high results as other substances besides ammonia, 

 such as amino acids (see p. 127) react with formaldehyde. The 

 second method consists in distilling the ammonia by a current 

 of air at a low temperature after the addition of a weak base 

 such as magnesium carbonate.f 



Uric Acid. This substance is mainly the. end product of 

 the decomposition of nucleo proteins. Nucleo proteins are 

 split into nuclein and protein. Nuclein is hydrolysed into 

 nucleic acid and protein. Nucleic acid is decomposed into 

 phosphoric acid, carbohydrate and purine bases andpyramidine 

 bases. All these changes are brought about by hydrolysing 

 enzymes. The purine bases are deamidised by enzymes and 

 the resulting hypoxanthine and xanthine are oxidised to uric 

 acid. 



The excretion of uric acid depends partly on amount of 

 purine substances in the diet and on its formation in the body 

 by the decomposition of nucleo protein according to the follow- 

 ing schema : { 



* A. Ronchese, Soc, biol., 1907, vol. 62, pp. 779 and 867. 

 f O. Folin, Zeit. physiol. Chem., 1992, vol. 37, p. 161. 

 J W. Jones, Nucleic Acids, Longmans, Green & Co, 1914. 

 Plant (yeast) nucleic acid differs from animal nucleic acid in contain- 

 ing pentose instead of hexose and uracil instead of thymine. 



