INTESTINAL SYNTHESIS 



indirectly by synthesis carried out by the extensive bacterial flora of 

 the intestines ". 



Thirteen years later, Bechdel et al^ showed that calves developed 

 normally on a diet low in " vitamin B ", and they therefore supported 

 the hypothesis put forward by Theiler et at. Later work, however, 

 indicated that the source of the vitamin B in ruminants is the bacterial 

 flora not of the intestine, but of the rumen. Nevertheless, recent 

 work has confirmed in a most dramatic manner the prophetic words 

 of the South African workers in respect of other species of animals. 



Most of the early results on aneurine excretion in animals were 

 confined to estimates of urinary excretion, and no reports appear to 

 have been made of the amounts excreted in faeces until 1935, when 

 Guerrant et al.^ showed that vitamin B^ was present in the faeces of 

 rats owing to bacterial synthesis in the caecum. In the rat the 

 nature of the ingested carbohydrate had a marked effect on the 

 elaboration of the vitamin, readily assimilable carbohydrates such as 

 sucrose and glucose being ineffective. Dextrin, however, was assimi- 

 lated at a much slower rate, enabling it to reach the caecum where 

 organisms had an opportunity of multiplying. For many years it was 

 believed that rats could only benefit from this microbiological syn- 

 thesis by ingesting their faeces * and, in fact, they may do this in vita- 

 min Bj deficiency tests unless prevented from gaining access to their 

 faeces, for instance, by using cages with wire-screens ; many experi- 

 ments have been invalidated through failure to take precautions 

 against this contingency. 



Refection 



In 1926 it was reported by L. S. Fridericia ^ in Denmark that a 

 young rat on a *' vitamin B "-deficient diet containing rice starch had 

 begun to grow at a normal rate, after its weight had declined in the 

 anticipated manner. At the same time, the faeces became white and 

 bulky owing to the presence of undigested starch. The phenomenon 

 was termed refection, and appeared spontaneously some months later 

 in a group of rats at the Lister Institute, London.^ It could be 

 induced in any rats by feeding the bulky white faeces. The pheno- 

 menon is due to the sudden loss by the rat of the ability to digest 

 starch, though why this should happen is still a mystery. It has been 

 suggested ^ that the presence of undigested starch and of starch- 

 splitting organisms in the caecum leads to a vigorous fermentation 

 with the development of an acid pH that favours the growth of 

 organisms capable of synthesising members of the vitamin B complex. 

 These then become available to the rat by virtue of the acid pK of 

 the caecum, and the caecal region therefore behaves like the rumen 



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