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Sofia E. Kjellman grapples with her carbon dioxide output resulting from her work as a scientist. Sofia E. Kjellman grapples with her carbon dioxide output resulting from her work as a scientist.

IN previous articles1–3 attention was directed to the fact that high pressures of pure oxygen have a specific effect on the metabolism of cells of various kinds. In the tissues of higher plants the effect was shown to be the stopping of carbon dioxide output, and this, it was postulated, was the result of the inactivation of the associated enzyme systems. In some fungi and in two species of bacteria it was shown also that exposure to 10 atm. pressure of pure oxygen completely suppressed the growth of the organisms. However, unlike the tissues of higher plants, the fungi, when removed from the pressure and returned to air, recovered and began to grow apparently quite normally if the period of exposure were not too long. In these cases a period of some days normally elapsed before the growth of the colonies in air began again. All the fungi were grown on 2.5 per cent malt agar in Petri dishes and the temperature was maintained at 25° C in a constant-temperature room or in an incubator.

IN assessing changes of vital function during electronarcosis, we measured oxygen consumption and carbon dioxide output in an experiment in rabbits. The measured values were considered an important index for the evaluation of metabolic changes during electronarcosis.

CARBONIC anhydrase which catalyses the reversible reaction H2CO3 ⇄ CO2 + H2O is present in large concentrations in the red blood corpuscles and some cells of gastric mucosa of mammals. This enzyme plays an important part in accelerating the carbon dioxide output in the lungs; it appears also to promote the formation of hydrochloric acid by the parietal cells of gastric mucosa1.

RECENT work in this Laboratory1 has shown that succinic acid may not only inhibit oxidative processes, as shown by earlier workers2, but also it may be actually toxic to plant material. Succinate supplied to respiring disks of apple peel (in a suitable buffer system at pH 4.1) at concentrations greater than about 0.025 M reduces oxygen uptake and carbon dioxide output, and in a comparatively short time the respiration falls practically to zero and the tissue becomes brown and ‘dead’. At this external concentration of succinate the internal concentration is less than 0.001 M.

THE phenomenon of climacteric rise in respiration of ripening fruits is not fully understood. Blackman and Parija1 explained the rise in respiratory activity in apples on the assumption that in the senescent stage a lowering of ” hydrolysis-resistance” occurs leading to a greater production of effective substrate for respiration. Kidd and West2 have attributed the initial increase in carbon dioxide output during senescence to the action of some ” protoplasmic factor”. Gustafson3 has demonstrated that the rate of respiration is very greatly influenced by the pH of the cell-sap, lower values of pH being usually associated with higher rates of respiration, and in a later communication4 suggests that the climacteric rise is probably due to a lowering of pH, of the cell-sap.

Ball, Dyke and Wilkins1 and Wilkins2 developed an apparatus, incorporating an infra-red gas analyser (Grubb-Parsons, S.B.1), for continuously estimating the rate of carbon dioxide metabolism of plant tissue maintained under constant external conditions for 5–10 days. Using this apparatus the rate of carbon dioxide output of individual adult cockroaches was determined. The insects were kept in 12 : 12 hr. alternations of light and darkness and, at the commencement of an experiment., were transferred to a small flask which was placed in darkness and at a constant temperature at the end of a light period. The records presented here were derived from one insect, but five other cockroaches gave closely similar results.