Absorption, Metabolism, and the Diet - 347 



Table 18-2*— Character of Proteins in Some Common Foods 



Italicized amino acids are essential. 



* From Best and Taylor, The Living Body, 4th Ed., 



vitamin necessary to the species is regularly 

 absent from the diet, the animal begins to 

 show specific symptoms, which can be recog- 

 nized as one of the deficiency diseases, or 

 avitaminoses, and eventually the animal dies 

 unless the deficiency is corrected. 



Because of its historic interest, vitamin C 

 will be used to exemplify the vitamins gen- 

 erally. Scurvy, the avitaminosis which devel- 

 ops when vitamin C is absent from the diet, 

 was described very accurately by Richard 

 Hawkins, more than 350 years ago. Hawkins, 

 a captain in the English navy, observed the 

 bleeding gums, bruised skin, anemia, and 

 general weakness that developed in the crew 

 when a sailing vessel had been at sea for 

 many months and all supplies of fresh fruits 

 and vegetables had been exhausted. Hawkins 

 also observed that a small amount of lime 

 juice, added to the daily menu of the crew, 

 was completely effective in preventing the 

 development of the scorbutic symptoms. 



In 1933, Albert Szent-Gyorgyi, the well- 

 known Hungarian biochemist and Nobel 



1963. 



laureate, now working in the United States, 

 first succeeded in isolating and purifying 

 vitamin C — which proved to be ascorbic acid 

 (C 6 H s O ). Meanwhile, many other vitamins 

 have now been identified (Table 18-3), and 

 all have been found to be relatively simple 

 organic compounds that can be absorbed 

 without digestion— if they are present in the 

 foods of the animal. Moreover, each vitamin 

 is specific in relieving the particular symp- 

 toms caused by its deficiency. Only ascorbic 

 acid (or compounds from which the body can 

 derive ascorbic acid) is effective in prevent- 

 ing or relieving the specific symptoms of 

 scurvy (Fig. 18-2). 



In scurvy, the main symptoms are gener- 

 ally attributed to a weakening of the walls 

 of the arterioles and capillaries. The scor- 

 butic animal displays spontaneous bleeding 

 — in the gums and joints, and beneath the 

 skin — and this may account for the fact that 

 scorbutic individuals are very susceptible to 

 bruises. Probably the anemia is likewise a re- 

 sult of internal bleeding, although some re- 



