CH. XIV.] ANALYSIS OF FLUIDS. 369 



cane sugar is hydrolysed very easily, starch, etc., are only slowly 

 acted on. 



8. Starch, glycogen and the erythro-dextrins do not give any 

 colour with iodine solutions, if the reaction of the fluid be alkaline. 

 If this be the case, make the reaction acid with acetic acid. 



9. The proteins interfere with the iodine tests for these 

 substances, and should therefore as far as possible be removed 

 before testing for the polysaccharides. 



10. Fat is insoluble in water, so do not waste time in testing 

 an ordinary solution for fats. 



11. The only reliable test for urea is the urease test (Ex. 343). 

 In this connection it must be remembered that urea is soluble in 

 alcohol, and can thus be separated from the proteins and other 

 substances likely to interfere owing to their " buffer " action. 



12. Ammonium chloride is a very valuable reagent in testing 

 for uric acid or urates. The only other physiological substance 

 precipitated by it is soap. 



13. Never omit " control " tests when investigating the 

 ferment action of a solution. 



14. Use " carmine fibrin " in testing for pepsin ; never when 

 testing for trypsin. 



15. In testing solutions for pigments, examine spectroscopi- 

 cally in various dilutions. Note the reaction of the fluid ; it is 

 no good looking for haemochromogen in a markedly acid solution. 



16. Creatinine, acetone, aceto-acetic acid and lactic acid can 

 usually be identified by specific colour reaction, though the latter 

 generally involves an extraction with ether. Creatine can only be 

 identified after conversion to creatinine, and then an estimation of 

 total creatinine is necessary. 



17. A solution of amino-acids evolves nitrogen gas with 

 nitrous acid and also with alkaline hypobromites. Ammonia can 

 be removed by gentle boiling in an open dish with a little alkali. 



AA 



