244 



VITAMINS 



Table 9-5 

 Pyridoxine content of common foods 



Milligrams per 100 g. 

 edible portion 



Beef, lean 0.40 



Beef, liver 0.73 



Bread, white 0.30 



Bread, whole wheat 0.70 



Cabbage 0.29 



Carrot 0.19 



Chicken, dark meat 0.20 



Lamb, leg of 0.38 



Milk, whole '. 0.20 



Oatmeal 0.25 



Pork loin 0.60 



Potatoes, white 0.16 



Yeast, dried brewer's 5.5 



BIOTIN 



This member of the vitamin B complex is a substance which has been 

 variously known as "coenzyme R," "vitamin H," "biotin," and the "anti- 

 egg white injury factor." It was first obtained in pure form and given 

 the name biotin in 1936 by Kogl, who was studying it as one of the 

 vitamin-like substances required for normal yeast growth. 



Physiological function 



The feeding of biotin brings about the cure of a nutritional disease 

 which develops when rats, chickens, or human beings consume large 

 amounts of raw egg white. This "egg white injury" disease is primarily 

 a dermatitis, characterized in the rat by swelling and inflammation of 

 the skin, especially around the mouth, and by loss of hair. The disease 

 is actually an induced biotin deficiency caused by the combination of 

 the biotin normally present in the food with a particular protein, avidin, 

 present in raw egg white. When so combined, biotin cannot be absorbed 

 and utilized by the animal organism. Cooked egg white on the other 

 hand is perfectly safe in the diet, since heating to 100°C. destroys the 

 ability of avidin to combine with the vitamin. 



Although the above facts demonstrate that biotin is an indispensable 

 nutrient, it has not been possible to produce the "egg white injury" dis- 

 ease in rats by feeding them diets extremely low in biotin. Apparently 

 a sufficient supply of the vitamin to meet the needs of the animal is 

 synthesized by bacteria in the intestinal tract. However, this deficiency 

 can be produced in the chick without the use of raw egg white. Like- 



