PHYSIOLOGY 



only the bricks out of which the body is built 

 (proteins or albumins, starches, sugar, fat, salts, 

 and water), but in addition minute amounts 

 of certain accessory materials, which make body- 

 building possible, and without which growth, 

 health, and even life itself are impossible. It is to 

 these accessory materials that the name ' vitamins ' 

 has been given. They are present in such small 

 amount that it is only quite recently that their 

 presence has been demonstrated, and even now 

 we are ignorant of their chemical nature. They 

 are all ultimately products of the plant-world, 

 and it has been shown that there are several of 

 them. They differ in their distribution and solu- 

 bilities ; when they are withheld from the food, 

 diseases which are called ' deficiency diseases ' 

 occur. Up to the present, research has centred 

 around three of them ; they have been labelled 

 A, B, and C. 



Vitamin A is contained in the green parts of 

 plants, and it is readily soluble in fats. When the 

 cow eats grass this vitamin passes into her milk, 

 and gives to butter its supreme value as compared 

 with butter-substitutes made by hardening vege- 

 table oil, where, owing to the high temperature 

 employed in their manufacture, any vitamin which 

 might have been present is destroyed. In animals 

 which ultimately rely on marine vegetation, such 

 as the fishes, the vitamin is mainly stored in the 



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