Letters to the Editor

Dr Houck is quite right in stating that there is little information on the actual vitamin requirements for low birth weight infants with a few exceptions. One liter of most infant formulas contains somewhat more than the recommended daily allowances for a young term infant in the first few months of life. An infant taking one tenth this volume would, of course, receive very small amounts of vitamins; however, vitamins are necessary for growth and, in rapidly growing infants, the vitamin requirement would be expected to be increased.

Effect of Graded Levels of Supplemental Ascorbic Acid in Practical Diets Fed to Rainbow Trout (Salmo gairdneri)

Deficiency symptoms, including anorexia, lethargy, lying prostrate at the bottom of the tank, scoliosis, and lordosis, were noted 20 wk after the start of the experiment in rainbow trout (Salmo gairdneri) held at 15 °C and fed a diet with no supplemental ascorbic acid. The apparent requirement was 40 mg/kg of supplemental ascorbic acid; however, the amount added to trout diets should be in excess of this level due to processing and storage losses and other factors. The ascorbic acid requirement for rainbow trout appears to vary with the age and rate of growth of the trout in that the requirement is higher in young fish. Ascorbic acid was noted to function in the iron metabolism of rainbow trout. Liver and spleen iron levels were correlated with the ascorbic acid level in the diet and suggest either a redistribution of iron stores due to impaired release of iron from reticuloendothelial stores or an increase in the efficiency of intestinal iron absorption. Scorbutic trout developed a gradual but progressive anemia. Key words: ascorbic acid, rainbow trout, vitamin requirement, iron, mineral metabolism, anemia

A microbial interaction involving combined mutualism and inhibition

A defined medium deficient in both niacin and biotin supported neither Proteus vulgaris nor Bacillus polymyxa in pure culture, but a mixed culture grew well. Presumably each can supply a vitamin requirement for the other. Continuous flow cultivation of mixed cultures exhibited oscillatory population levels of each species. P. vulgaris produced an inhibitor which accumulated to inhibit growth of B. polymyxa, and the vitamin interdependency caused the former to also cease growing. After continued pumping diluted the inhibitor, growth resumed. The inhibitor seems to be a protein, because proteolytic enzymes added to the culture gave higher, non-oscillatory population levels.

Effeots of High Temperature and Genotype on the Growth of Excised Roots of Arabidopsis Thaliana

The effects of a high temperature (31'5�C), and the addition of vitamins (thiamine plus biotin) on the growth of excised roots of four clones of A. thaliana derived from the strains EST, Pi, BLA, and 1018/6 are described. Growth response of the roots to these treatments was different from that of the whole plant of the same strain. The vitamin requirement of the roots of strain 1018/6 was greater at 31� 5�C than at 27�C.