Licence: In copyright
Credit: A manual of physiology : with practical exercises / by G.N. Stewart. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![[ 24^ ] SCHEME FOR TESTING A SOLUTION FOR THE MORE COMMON PROTEIDS AND CARBO-HYDRATES. 1. Note the reaction, and whether the liquid is coloured or colourless, clear or opalescent. A reddish colour suggests blood; opalescence suggests glycogen or starch. Try one or more of the general proteid tests {eg., the xantho-proteic or biuret). If the result is positive, proceed as in 2 ; if negative, pass to 3. 2. Test for Proteids.—(1) If the reaction is acid or alkaline, neutralize with very dilute sodium carbonate or sulphuric acid. A precipitate = acid- or alkali-albumin, according as the original reaction is acid or alkaline. If the original reaction is neutral, no acid- or alkali-albumin can be present in solution. Filter off the precipitate, if any. (2) Boil some of the filtrate from (1) (or of the original solution if it is neutral), acidulating slightly with dilute acetic acid. A precipitate = albumin or globulin. Filter, and keep the filtrate. (3) If a precipitate has been obtained in (2), (a) saturate some of the original solution with magnesium sulphate, or half saturate it with ammonium sulphate (*.*., add to it an equal volume of saturated ammonium sulphate solution). If there is no precipitate, globulin is absent, and therefore the precipitate obtained in (2) must be albumin. A precipitate = globulin. But albumin may also be present in the solution. To see whether this is so, filter off the globulin and boil the filtrate after acidulation with acetic acid. A precipitate = albumin. (b) Keep a small portion of the filtrate. Saturate the rest of the filtrate from (2) with ammonium sulphate. A precipitate = proteose. Filter from (2) for (d). (r) To the filtrate from (6) add excess of solid sodium hydrate in small pieces at a time. Much ammonia is given off. Allow the test-tube to stand fifteen minutes, shaking it at intervals. Then add dilute cupric sulphate, and if much of the sodium sulphate formed remains undissolved, add water to dissolve it. A well-marked rose colour = peptone. (d) If proteoses have been indicated by (b), confirm by adding to the filtrate from (2) strong nitric acid. A precipitate which disappears on heating and reappears on coolings proteose. But one of the members of the proteose group, deutero-albumose, is not precipitated till sodium chloride is added as well as nitric acid. This reaction will not detect small quantities of proteose. (4) If no precipitate has been obtained in (2), the solution contains neither albumin nor globulin. To test whether proteose or peptone is present apply (3) {b), (c), and (d). 3. Test for Carbo-hydrates.—Use the original solution, freed from coagulable proteids, if such have been found, by acidulation and boiling. (1) Add iodine. If the solution is alkaline neutralize it before adding the iodine. A blue colour— starch. Confirm by boiling with dilute sulphuric acid and testing for reducing sugar., A reddish-brown colour = glycogen or dextrin. Glycogen gives an opalescent, dextrin a clear, solution. Glycogen is precipi- tated by basic lead acetate, dextrin is not. Both are changed into reducing sugar by boiling with dilute acid. (2) Add to some of the original solution cupric sulphate and excess of sodium hydrate, and boil. Yellow or red precipitate = reducing sugar. (3) If (1) and (2) are negative, boil some of the liquid with one-twentieth of its volume of strong hydrochloric acid for fifteen minutes, and test as in (2). A red or yellow precipitate shows that cane-sugar was originally present, and has been inverted.](https://iiif.wellcomecollection.org/image/b21932967_0031.jp2/full/800%2C/0/default.jpg)
