Chapter XI 

 Function of Carotinoids in Plants and Animals 



The significance of the chromolipoids in the metabolism of the liv- 

 ing organism? in which they are found has not been discovered. Their 

 almost universal occurrence in vegetative organisms and their very 

 frequent appearance in animals naturally leads to the belief that they 

 perform some function in the economy of life. It is natural for the 

 biochemist to seek for the basis of the occurrence of any wide-spread 

 substance or group of substances in living matter but so far as the caro- 

 tinoids are concerned their significance and possible functions have not 

 got beyond the realms of speculation. In presenting the theories which 

 have been advanced it seems best to consider the plant side of the ques- 

 tion separately from that of the animal. There are several reasons for 

 this. In the first place the carotinoids have their origin in the plants 

 and occur in animals only as they are present in the food. In fact, as 

 already pointed out in a previous chapter, the ability to synthesize the 

 carotinoids may well serve as one of the means of distinguishing plants 

 from animals. In the second place the question has recently been 

 raised as to whether the carotinoid pigments are identical with vitamin 

 A, or related to these unknowns which play so important a part in the 

 nutrition of animals. This question is properly considered in connec- 

 tion with the possible function of the carotinoids in animal life. 

 Finally, the occurrence of carotinoids in certain species of animals, 

 such as fowls and cattle, has come to have a practical significance in 

 connection with the use to which man has put these animals in the 

 production of eggs and milk. 



Before discussing these questions, some of which have a practical 

 as well as a biochemical point of view, it is not altogether unreasonable 

 to ask why it is necessary to consider that the carotinoids must play 

 a role in metabolism merely because they are of wide-spread occur- 

 rence. It is not a new idea that the lipochromes in animals are of the 

 nature of waste products of the organism. Although this idea was 

 advanced while the belief was generally held that animals synthesize 



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