METABOLISM 281 



Accessory Factors. — By feeding young rats upon diets 

 containing an adequate amount of pure proteins, fats, 

 carbohydrates, and inorganic salts, it has been shown that 

 growth is arrested unless two substances, the chemical 

 nature of which is still unknown, are present. 



(1) Fat Soluble A. — This usually occurs in close con- 

 nection with animal fats. It is particularly abundant in 

 milk fats and in cod-liver oil. It is also present in green fodder. 



In rats its absence from the diet not only causes an 

 arrest of growth, but also a peculiar inflammation round the 



eyes. 



Rickets is a disease affecting young animals, notably 

 dogs. It is characterised by such constitutional symptoms 

 as muscular weakness, and by changes at the epiphyseal 

 cartilages, and softening of the bones, either due to loss 

 of hme salts or to failure in calcification. An attempt 

 has been made to explain it as a result of a deficient 

 supply of the fat soluble A or of some allied substance, 

 but no sufficient evidence has been adduced in proof of 

 this, and the cause of the disease is still unknown. 



(2) Water Soluble B. — (a) Anti-neuritic. — This is present 

 abundantly in the germs of plants, but not in the endosperm, 

 in young leaves, and in flesh. Its presence is necessary for 

 growth, and it is at least probable that when the supply is 

 insufficient symptoms of neuritis may develop. 



A disease known as beri-beri develops in people living 

 too exclusively on polished rice, which is poor in this sub- 

 stance. A polyneuritis which is substantially the same as 

 beri-beri can be similarly produced in animals and especially 

 in fowls. This condition can be cured by adding substances 

 containing water soluble B in the diet. Hence it has been 

 called an anti-neuritic substance. 



(b) Anti-scorbutic A closely- allied substance, abundantly 



present in orange and lemon juice and in many fruits and 

 vegetables, seems to be essential, and in its absence scurvy 

 is apt to develop, either in men or animals. It may be 

 called the anti-scorbutic substance. 



Practically nothing is known about the relation of these 

 substances to one another. 



