Abstract
None of the ordinary constituents of body fluids interferes with the test outlined below, save a substance in the urine, as yet unidentified, but which is probably a small amount of oxalic and perhaps glyoxalic acids, which have been reported as occuring freely in urine by Fürbinger 1 and by Granström 2 , respectively. Creatinin, creatin, uric acid, etc. are negative. Allantoin, however, may be separated from the other constituents of the urine by precipitation with ammonical silver nitrate. Then the allantoin is subjected to the test. This procedure is necessary only in the case of urine for blood and other body-fluids show no interfering substance.
To 25 mg. filtered urine, add, if necessary, 10 per cent hydrochloric acid to slight acidity; if the urine is initially acid, this is unnecessary. Then add, drop by drop, 1 per cent aqueous solution silver nitrate until no more precipitate of silver urate is obtained; ten drops are usually sufficient. Let stand five minutes, filter, saving the filtrate. Or, one may use a 50 mg. centrifuge tube and precipitate by means of the centrifuge.
A test for the presence of uric acid on this filtrate may be made by Folin's test. Then add, drop by drop, concentrated ammonium hydroxid to the filtrate to obtain the precipitate of allantoin silver nitrate; in case, after the addition of two drops of the ammonia, no precipitate appears, add a drop lor two of silver nitrate solution as before, to insure that all of the silver nitrate first used was not carried down as silver urate. An excess of ammonia causes solution of the precipitate.
A precipitate, varying with the amounts of allantoin, may be obtained by centrifuging. Procedure for all fluids: To a few mls. of the fluid, or to the precipitate obtained above after decantation of the supernatant fluid, add one small flake of indol, a commercial product.
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