. Principles of modern biology. Biology. Absorption, Metabolism, and the Diet - 351 malfunction. Moreover, two of the fat-solu- ble group, namely A and D, are the only vitamins that are known to have deleterious effects when taken in great excess. Previously the B-complex of vitamins was thought to be a single compound. Now, how- ever, at least ten separate B vitamins have been identified, although not all of these will be discussed. A deficiency of thiamine, or vitamin Bx, gives rise to polyneuritis, or beriberi, as it is usually called in man. Drastic polyneuritis involves degenerative chang
. Principles of modern biology. Biology. Absorption, Metabolism, and the Diet - 351 malfunction. Moreover, two of the fat-solu- ble group, namely A and D, are the only vitamins that are known to have deleterious effects when taken in great excess. Previously the B-complex of vitamins was thought to be a single compound. Now, how- ever, at least ten separate B vitamins have been identified, although not all of these will be discussed. A deficiency of thiamine, or vitamin Bx, gives rise to polyneuritis, or beriberi, as it is usually called in man. Drastic polyneuritis involves degenerative changes in the nerves and a severe progressive paralysis. The pa- ralysis disappears very rapidly, however, when thiamine is given. A polyneuritic ani- mal frequently regains normal muscular Fig. 18-3. Upper photograph: Drastic vitamin A defi- ciency in a white rat, showing blindness as a result of an ulceration of the cornea. Lower photograph: Restor- ation of the eyes after feeding adequate quantities of vitamin A. In some cases a deficiency of the fat-soluble vitamins may result, not so much from their lack in the diet, but more from a failure in their absorption. Because bile salts are nec- essary for this absorption, deficiencies may arise in cases of gall bladder or other liver. Fig. 18-4. Upper photograph: Pigeon suffering from polyneuritis. Lower photograph: Same bird less than 3 hours after treatment with thiamine (vitamin Bx).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Marsland, Douglas, 1899-. New York, Holt, Rinehart and Winston
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