470 



ORGAN SYSTEMS OF MAN 



recovered almost miraculously, if the ship 

 docked where fresh fruits were available. 

 He, therefore, took fruit, particularly citrus 

 fruit, aboard and discovered that small 

 daily rations kept his men from getting the 

 dreaded scurvy. It has been said by some 

 that the use of this knowledge was respon- 

 sible in part for the success of the British 

 navy. Within the present century a great 

 deal has been learned about this vitamin, as 

 well as many others that have since been 

 discovered. 



Vitamins are effective in extremely small 

 quantities, so small that they cannot be con- 

 sidered energy-producing in the sense that 

 proteins, carbohydrates, and fats are. They 

 are specific, relatively simple organic com- 

 pounds which must be included in the 

 diet for normal health. If they are absent 

 over a period of time, definite symptoms 

 appear which grow progressively worse, 

 terminating in death. Animals vary in their 

 vitamin needs. Rats, for example, can 

 synthesize vitamin C and man can exist 

 without thiamine. In the latter case, how- 

 ever, this vitamin is manufactured by bac- 

 teria living in his digestive tract. By trial 

 and error experiments the vitamin require- 

 ments have been determined for most labo- 

 ratory animals, such as the rat, mouse, 

 guinea pig, and rabbit, so that they can be 

 employed in vitamin research. However, in 

 recent years it has been found that micro- 

 organisms, such as certain species of bac- 

 teria and Protozoa, also require vitamins, 

 and their needs are so precise that these 

 tiny organisms have become very important 

 in determining not only the presence of par- 

 ticular vitamins in foods but also the 

 amount present. This method, called micro- 

 biological assay, is becoming more impor- 

 tant as further studies are made on nutri- 

 tion. 



Vitamin research is moving so rapidly 

 today and becoming so complicated that 

 only a bare minimum can be presented here 

 — enough, it is hoped, to provide the reader 

 with sufficient knowledge to approach the 



problem of feeding himself in an intelligent 

 manner. Some of the better-known vitamins 

 are listed in Table I, together with their 

 sources and the diseases caused by their 

 absence from the diet. 



Vitamin A. This vitamin is derived from 

 the orange-colored pigment of plants called 

 carotene. Strangely enough, the vitamin 

 itself in pure form is colorless. Carotene is 

 present in all green plants and it is most 

 abundant in those that are yellow or red. 

 Carrots, for example, are rich in vitamin 

 A. Some animals have a tendency to store it 

 in great quantities in their livers. This is 

 particularly true of such fish as the shark, 

 cod, and halibut, hence the well-known 

 names — shark-liver oil, cod-liver oil, hali- 

 but-liver oil. Note that it is found in the 

 oil of these livers. Its fat or oil solubility is 

 one of its characteristics. 



In severe cases of vitamin A deficiency, 

 rarely observed in this country, the eyes be- 

 come infected and the cornea becomes very 

 dry and ulcerated. Another symptom is the 

 inability to see at night, which is called 

 night blindness. The retina of the eye can- 

 not synthesize visual purple in the absence 

 of this vitamin and consequently does not 

 respond to dim light (see p. 401). It is 

 true of vitamin A, as it is with most of the 

 others, that severe symptoms resulting from 

 a marked deficiency rarely show up among 

 Americans because of our diversified diet. 

 Mild cases, on tlie other hand, are relatively 

 common but can be corrected simply by 

 supplementing the diet with vitamin A. 



B vitamins. This is a group of vitamins 

 that are abundantly found in high-protein 

 foods such as meat, liver, nuts, whole 

 grains, and particularly yeast. In the early 

 days of vitamin research, a single B vitamin 

 was described; now a large number, up- 

 wards of 12, are known to belong to this 

 group which is sometimes referred to as the 

 B complex. They do not all function di- 

 rectly in nutrition, however. 



Thiamine ( Bi ) produces dramatic results 

 when administered to a laboratory animal, 



