Most herbivorous animals and some carnivorous animals, like man, are able 

 to produce vitamin A from carotin. Other carnivorous animals — cats, for 

 example, and carnivorous fish — lack what it takes to transform carotin 

 into vitamin A. 



In both plants and animals vitamin D results from the action of sunlight 

 on ergosterol, a fatty substance. Ergosterol, however, originates, so far as 

 we know, only in plants. Many mammals (though not man, the monkey, 

 or the guinea-pig) are able to synthesize ascorbic acid. 



The cow can thrive without taking vitamin B in her food. Apparently, 

 certain species of bacteria that live in the rumen, or paunch, of the animal's 

 complex "stomach" are able to make thiamin out of other materials. Ex- 

 periments have been carried on to see whether it is possible to domesticate 

 such bacteria in the human intestine and so make it unnecessary for us to 

 get thiamin with our food. 



Our knowledge of the functions of the vitamins in the animal body is 

 dependable, so far as it goes. However, not all the vitamins have been 

 clearly identified as definite chemical compounds. Until we are sure that 

 all the substances that are known by a particular name really are the same 

 substance, we cannot be sure that the effects observed in organisms are 

 always due to the vitamin (or whatever other class of materials) to which 

 we have attributed them. 



Until recent years the various vitamins have not been available in large 

 quantities. However, improved methods of isolating or producing them 

 are being developed. With adequate supplies of pure materials, and with 

 improved techniques for dealing with them, we may hope to solve many 

 of the outstanding nutritional problems. At the same time, having large 

 quantities of certain vitamins enables us to remedy deficiencies in diet 

 among masses of our population. 



With all these gains, there is real danger. For we are all naturally Im- 

 pressed by the dramatic achievements of "vitamin cures". People may too 

 easily get the idea that we can prevent or cure all sorts of ills by feeding 

 ourselves assorted vitamins by the spoonful or in capsules. The indiscrimi- 

 nate use of vitamin concentrates for self-medication may introduce other 

 privations or deficiencies, as well as positive injuries. We are not yet cer- 

 tain what effects various vitamins may produce if used in excessive quan- 

 tities. Moreover, people can generally use their food money to better 

 advantage by going to natural foods for the vitamins they need. We cannot 

 afford to pay caviar prices for cabbage leaves. 



During the Second World War the British Ministry of Health con- 

 ducted two series of experiments to find out whether vitamin concentrates 

 were of any help to school children or to workers. Over a period of from 

 two to nine months, hundreds of children and of workers were supplied 



no 



