INTRODUCTION 



in common and that substances essential for the growth of uni- 

 cellular organisms were also necessary for the growth of their multi 

 cellular relatives. The clue thus provided was followed up, with 

 spectacular results. Another member of the bios complex is a sub- 

 stance called biotin, which has a demonstrable biological activity in 

 extremely high dilution. When biotin was administered to animals 

 suffering from so-called vitamin H deficiency the symptoms dis- 

 appeared, and thus another link was forged between the two groups. 

 In almost exactly the same way folic acid, a factor essential for the 

 growth of certain bacteria, was shown to be identical with a factor, 

 termed vitamin B,., necessary for the well-being of chicks. In this 

 instance, however, there exists a group of at least four closely related 

 factors exhibiting similar biological properties — a folic acid complex 

 within the vitamin B complex. Other examples of the identity of 

 growth factors for higher and lower organisms are provided by _/)-amino- 

 benzoic acid and inositol, both of which are essential growth factors 

 for many bacteria and yeasts and also essential vitamins for certain 

 species of animals. 



The discovery that ^-aminobenzoic acid was a growth factor for 

 bacteria led to another discovery of great theoretical significance 

 although not apparently of great practical importance. The discovery 

 of the growth-promoting properties of ^-aminobenzoic acid followed 

 the observation that it counteracted the antibacterial action of sul- 

 phanilamide, to which it is structurally analogous. This led to a 

 theory that bacterial growth may be inhibited by the addition to the 

 medium of a substance which antagonised the growth-promoting 

 action of an essential metabolite. 



Now every theory, to be of any value, should enable predictions to 

 be made, and the fulfilment of these predictions greatly strengthens 

 the theory from which they are derived. If, then, sulphanilamide 

 could reverse the growth-promoting effect of ^-aminobenzoic acid, 

 would substances chemically related to other members of the bios or 

 vitamin B complex inhibit bacterial growth by competing with these 

 vitamins in the metabolic processes going on within the bacterial cell ? 

 This question was asked — and answered in the affirmative — by groups 

 of workers in Great Britain, the U.S.A. and Germany. Pyridine-j8- 

 sulphonic acid was shown to antagonise the effects of nicotinic acid, 

 is oribo flavin e those of riboflavine, desoxypyridoxine those of pyri- 

 doxine, pantoyltaurine and many other related substances those of 

 pantothenic acid, and oxy biotin those of biotin. The use of such 

 antagonists has thrown a great deal of light on the function of the 

 vitamin B complex. 



Another important phenomenon that has recently come to light 

 as the result of work with sulphanilamide and related sulphonamides 



