PHYSIOLOGY, PHARMACOLOGY, AND TOXICOLOGY 385 



a proposal, however, does not at present seem sufficient to warrant its 

 general acceptance. 



Mental Activity. A further field of interest characteristic of animals 

 involves reflex and mental activity, and because of the pronounced defects 

 that occur in these functions in vitamin deprivation, various groups have 

 sought to establish some special relationship between them and the B 

 vitamins. To a large extent such attempts have been unsuccessful. There 

 is no doubt that mental activity as measured by sensory acuity and per- 

 formance tests of various kinds, reflex activity, and general personality 

 are all influenced greatly in B vitamin deficiency of even a mild nature. 

 Thus dogs that have developed conditioned reflexes to auditory stimuli 

 such that they showed a 100 per cent differentiation between two tones 

 for some months, lose their ability to differentiate in from four to fifteen 

 days on B vitamin-deficient diets. 45 While this loss became worse over 

 a two-month deficiency period, other deficiency signs were lacking in the 

 experiment. Vitamin supplementation rapidly restored the ability to dif- 

 ferentiate, and similar results were obtainable by repeating the sequence 

 on the same animals. 



A number of studies have been made to determine whether thiamine 

 supplementation improves the mental response of children, 46 - 47 and the 

 results have indicated that such is not the case when the individuals 

 concerned have an adequate thiamine intake. Similar results from adults 

 on adequate and restricted diets 48 - 50 seem to indicate clearly that inade- 

 quate B vitamin nutrition results in a frequently severe and general 

 breakdown in mental, personality and reflex processes, but that supple- 

 mentation with B vitamins above the level required for adequate nutrition 

 as assessed by other means has little or no beneficial effect. 



Pharmacological and Toxicological Effects 50a 



Previous mention has been made of the several important reasons for 

 a brief consideration of the pharmacodynamic action of the B vitamins. 

 Such a discussion might well be undertaken either from the standpoint 

 of the pharmacological effects observed in particular physiological sys- 

 tems, or in terms of the known effects of structurally similar compounds. 

 The latter alternative, i.e., the consideration of each B vitamin separately, 

 is here adopted because of the desirability of considering the picture so 

 obtained in the light of deficiency symptoms. The impetus of current 

 research in this field is such that what is at present a sparsely studied 

 topic may be expected to expand in the immediate future to a major field 

 of endeavor. Certainly such an event will be essential before a thorough 

 understanding of the biochemical processes involved in drug action can 

 be elucidated and drug design can become a science. 



