The availability of histidine derivatives for growth.

The purpose of the experiments to be described in this paper was to investigate whether the rat can synthesize the glyoxaline ring of histidine, if certain possible precursors are provided in the diet. It was first shown by Rose & Cox (1924) that a diet in which prottin was supplied in the form of a casein digest freed of histidine by silver precipitation could not support growth in young rats. This was later confirmed with synthetic diets (Rose, 1938). On the other hand Burroughs, Burroughs & Mitchell (1940) claimed that histidine is not necessary for the maintenance of nitrogen equilibrium in the adult rat, and Rose, Haines, Johnson & Warner (1943) found that a positive nitrogen balance could be maintained in man in the absence of dietary histidine. It appeared to us that these various and to some extent contradictory findings