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1. The oxygen consumption of normal and half-embryos ofXenopus laevis was measured by the automatic electromagnetic diver respirometer. 2. The rate of morphogenetic development of dorsal, left, and right half-embryos was found to be the same as in whole embryos but, in conformity with earlier observations, the development of ventral half-embryos is blocked. 3. Respiration of dorsal, right, and left half-embryos was found to be approximately half the normal, except in the initial cleavage period. Respiration of the ventral half-embryos, on on the contrary, failed to increase substantially by the time of gastrulation. 4. Our findings suggest a strict correlation between oxygen (and energy) consumption and epigenetic work.

The vitamin requirements of Thermobacterium acidophilum have been established. Five vitamins: Folic acid, nicotinic acid, pantothenate, pyridoxine and riboflavin have to be supplied. The vitamin concentrations necessary for the maximal growth were determined.

The utilization of various commerical di- and tripeptides and a preparation of phosphopeptides by Thermobacterium acidophilum was investigated. No peptide was utilized better than the corresponding free amino acids, but one, serylglycine, was used with equal efficiency. Of the ten amino acids contained in the phosphopeptides all could be utilized, but at a very slow rate. Only one amino acid, serine, could be utilized fast enough to permit a normal growth rate.