Vitamins and Antivitamins 31 



juice is like a machine-shop containing many large and complicated 

 machines. The tools used by these machines are, however, in short 

 supply, so the management, instead of firmly attaching each tool to a 

 machine, arranges to have them shared, so that each machine can 

 have the use of the tools when needed. 



Enzymes are so active that only small quantities of them are 

 required, and it is not surprising that minute quantities of the co- 

 enzymes are also sufficient. Prof H. Mcllwain has found that some 

 bacteria only have a few molecules of some of them in each cell. 



The co-enzymes are small molecules, and some of them have 

 been purified and their chemical structures ascertained (see Ap- 

 pendix). It has been found that they are closely associated with the 

 vitamins, being either the vitamins themselves or closely related to 

 them. This has been proved in at least eight cases so far, in which 

 the enzyme system with which the vitamin functions has been identi- 

 fied. For example, nicotinic acid is a constituent of the co-enzymes 

 of yeast juice; aneurin (vitamin Bl) is required by an enzyme called 

 carboxylase; riboflavin (vitamin B2) is the co-enzyme of several 

 coloured enzymes which bring about oxidations in the cell. 



The vitamins are required by animals, firstly because they cannot 

 make them themselves, and secondly because they are unable to 

 perform many of the vital processes of life without them. If the 

 vitamin is not present, the corresponding enzyme system is paralysed, 

 and the animal organisms function only imperfectly or not at all. 



Micro-organisms such as bacteria and fungi often need the same 

 vitamins which are required by animals. Eight essential substances 

 have been distinguished as essential to the life of micro-organisms — 

 and they all serve as vitamins for the higher animals. They are 

 aneurin (vitamin Bl), riboflavin (vitamin B2), pyridoxin (vitamin B6), 

 biotin (vitamin H), pantothenic acid, folic acid, co-enzyme I or its 

 components, and choline. Readers who are interested will find the 

 formulae of these compounds in the Appendix (p. 163). The ability 

 to synthesize these substances is very haphazardly distributed among 

 micro-organisms. Some, like yeasts, have a considerable ability of 

 making vitamins and are in fact rich sources of some of them. The 

 wild mould Neurospora crassa needs only glucose, ammonia, and 

 biotin in order to live; all other necessary substances it can make for 

 itself. Other micro-organisms can only grow if they are provided 

 with certain of these substances; they are unable to make them for 

 themselves, and they must have them if they are to grow. It was 

 found that some animals seemed to get along quite well on diets 

 which lacked some of the B vitamins. There was no evidence that 

 the animal itself was capable of synthesizing them. The mystery was 



