212 NUTRITION 



There are three such food factors hitherto recognised : — 



1. Fat-soluble A. — ^This substance is contained in most 

 animal fats and oils. It is present also in the seeds and 

 green leaves of plants, where its synthesis evidently occurs. 

 Insoluble in water, it is soluble in anything which dissolves 

 fats. It is destroyed by heating at 100° C. for four hours. 

 Though not synthesised, it is evidently stored in the 

 animal body, probably in the depot fat, for when the 

 substance is withdrawn from the diet there is a shght delay 

 before signs of malnutrition set in. 



Present-day evidence suggests that deficiency of this 

 substance is the primary cause of rickets. 



2. Water-soluble B. — This substance is present in all 

 foodstuffs in their natural condition. It is most abundant 

 in yeast, in the embryo of seeds and in birds' eggs. It is 

 soluble in water and alcohol, but not ether. It is resistant 

 to drying and to heat at 100° C, but it is destroyed 

 at higher temperatures. When it is absent from the diet 

 pathological effects follow immediately, showing that it 

 is not stored in the body. Recovery is equally rapid on 

 its restoration. Deficiency of Water-soluble B causes a 

 profound disturbance of the cerebral nervous system- 

 muscular weakness and inco-ordination. Now a similar 

 disturbance is found in the disease beri-beri, which occurs 

 in communities where the sole diet consists of maize from 

 which the embryo has been removed in the process of 

 mining. An analogous condition produced in birds by 

 similar feeding is called avian polyneuritis. It is beheved 

 by some that the " anti-nenriiic " substance whose absence 

 is responsible for beri-beri and polyneuritis is identical 

 with Water-soluble B. 



3. Anti-scorbutic. — This is the substance the absence of 

 which causes scurvy. It is present in tissues ujjiich are 

 metabolically active ; it is absent from dry seeds, for instance, 

 but appears on germination. It is readily destroyed by 

 heat. It is present most abundantly in cabbage leaves, 

 in lemons and in oranges. 



