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Vitamin C, the antiscorbutic vitamin
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Vitamin C is water-soluble and is found chiefly in fresh fruits and vegetables, but its distribution is not very uniform. Lemon juice is very easily oxidized, particularly in alkaline solution. Lemon juice left exposed to the air loses all its vitamin C in three hours. It is readily destroyed by heat, but is sometimes present in canned or dried food if these are acid and have been preserved in the absence of air.
It has been synthesized from d-galactose, and exists in an oxidized and reduced form.
Most animals can manufacture it themselves, but they cannot make it in sufficient quantities and still need an outside supply for a healthy life.
The ease with which it is oxidized suggested that it acts at some point in tissue respiration and its absence leads to a breakdown of protoplasmic structure. The chief deficiency disease, associated with it, is characterized by haemorrhage of the limbs and jaws. This is presumably caused by an increased permeability of the walls of the blood vessels.
Ascorbic acid is normally excreted in the urine, but in certain infectious diseases it is found there in smaller quantities than normal, which suggests that it is being used up in the body. It has recently been shown that it inactivates diphtheria and vaccinia injected into rabbits. These facts say that its absence leads to a reduced resistance to infections. It is possible that it is used in the formation of antibodies.
Ex.11. Make up a short summary of text B out of the topical sentences. Use any of the following phrases:
1. The subject of the text is …
2. The author of the text says that …
3. He points out that …
4. Next the author emphasizes the idea that …
5. The author goes on saying that …
6. The text ends with …
7. The author concludes that …
Unit 13 Grammar: when, if + Participle II
Translate the following words and word combinations and remember them:
1. carbohydrate [‘ka:bou’haidreit]
2. polysaccharide [,poli’sækəraid]
3. starch [sta:t∫]
4. inulin [‘injulin]
5. cellulose [‘seljulous]
6. glucose [‘glu:kous]
7. fructose [‘frΛktous]
8. sucrose [‘sΛkrous]
9. to derive [di’raiv]
10. elimination [I,limi’nei∫n]
11. enormously [I’no:məsli]
12. sulphuric acid [sΛl’fjurik ‘æsid]
13. non-reducing [,nonri’dju:siŋ]
14. deoxy sugars [di’oksi ‘∫ugez]
15. explosive [iks’plousiv]
16. brewing [‘bru:iŋ]
17. to sweeten [swi:tn]
18. bitter taste [‘bitə’teist]
19. bloodstream [‘blΛdstri:m]
20. conventional practice [kən’ven∫ənl ‘præktis]
Date: 2015-10-18; view: 407; Нарушение авторских прав