Intestinal synthesis of vitamins of the B complex in chicks.

I. Chicks were reared in germ-free and conventional environments on diets devoid of one of each of the following vitamins: riboflavine, pantothenic acid, vitamin Be, vitamin B,,, folic acid, nicotinic acid, thiamine or biotin. When marked signs of deficiency began to appear the birds were killed. The livers and caecal contents were removed and assayed microbiologically for the vitamin omitted from the diet. 2. Negligible quantities of the omitted vitamin were detected in the caecal contents of the germ-free birds, but considerable amounts were found in corresponding samples from conventional birds. There was little evidence that signs of deficiency were less severe in the conventional birds. 3. It was concluded that all the vitamins tested were synthesized by microbial action in the gut of conventional birds but that the birds derived little benefit from the synthesized vitamins, with the possible exception of folic acid. 4. There were indications that the requirements for thiamine and pantothenic acid were higher in conventional than in germ-free chicks.