BIOLOGY IN HUMAN AFFAIRS 



are deprived of vitamin A. The odontoblastic membrane 

 surrounds the pulp of the tooth and lies in apposition to 

 the under surface of the dentine. From each odontoblast a 

 fiber extends through a tubule in the dentine to the base 

 of the enamel. The odontoblast forms dentine. Howe 

 states that when animals are deprived of vitamin A, the 

 odontoblasts revert to osteoblasts, or bone-forming cells, 

 and that subsequently bone deposits may be formed by 

 these cells. The frequent occurrence of pulp stones in the 

 teeth of animals deprived of vitamin A supports this 

 view. The importance of this vitamin for the health of 

 the teeth appears, therefore, to be very great. 



Vitamin B. Our knowledge of the specific effects of 

 deficiency of vitamin B, which is one of several water- 

 soluble nutrients, is less satisfactory than in the case of 

 vitamin A, because uncomplicated vitamin B deficiency 

 has less frequently been produced experimentally. By 

 vitamin B we designate the anti-beriberi principle, or 

 the anti-neuritic vitamin. There is little reason to doubt 

 that deficiency of this vitamin is the cause of the disease 

 beri-beri, which has taken millions of lives during the 

 last 2000 years. The disease occurs mainly among rice-eating 

 people who take polished rice as their principal food. Most 

 of the vitamin is concentrated in the germ and the bran 

 layer, both of which are removed in polishing. Beri-beri 

 is still one of the chief causes of infant mortality in the 

 Philippine Islands and in the East Indies. 



In vitamin B deficiency the nervous tissues suffer an 

 injury almost as specific as that suffered by the epithelial 

 cells in vitamin A starvation. The peripheral nerves are 

 first affected. They undergo degeneration, and the muscles 

 innervated by these nerves undergo atrophy. For these 

 reasons beri-beri patients suffer paralysis. 



An interesting effect of B deficiency is lack of appetite. 

 Experimental animals cease to eat their caloric require- 



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