Acidosis develops in the acclimatization to high altitudes and persists some time after the descent, during which time the subject feels more vigorous (Schneider). During acidosis the ventilation of the lungs is increased to such an extent that the alveolar air is increased, and therefore the 02 in the blood-plasma is increased and that in the hemoglobin is increased if it is not already saturated. Increased respiratory movements tend to increase the heart-rate and hence the circulation, with better oxygen transfer to the tissues and increased oxidation. This effect may be small, and may be too small to account for the total increase in metabolism, but is worthy of consideration. Rasmussen has shown mild acidosis in case of the hibernating wood chuck with very much lowered 02 tension of venous blood, but evi dently the sensitivity of the respiratory center falls during hibernation.
It was shown by Warburg that the metabolism of sea-urchin eggs may be stimulated, but these are to be considered irritable cells in the same class with muscle. It may be that the metabolism of all cells can be stimulated, but they are not equally sensitive. Changes in hydrogen-ion concentration of the sea-water effective on sea-urchin eggs are not nearly so effective on the cells of Cassiopea (possibly because the pH of the sea-water changes before reaching the cells). Benedict claims that the basal metabolism of the human body may be stimulated, but it is difficult to estimate basal metabolism on account of the unavoidable activity of some excitable organs. Cutting the
nerves is of no advantage, since Langley and Itagski showed that the oxygen consumption of denervated muscle is much greater than that of normal resting muscle. What cells are stimulated in Benedict's experiments is not clear. He adds that changes in the pulse-rate accompany changes in the basal metabolism, and thus admits that irritable cells of the complex neuromuscular organization of the body are concerned in the phenomenon. If the respiratory or vasomotor centers are concerned in the increased metabolism, 02 tension in the tissues may be a factor. Verztir showed that resting muscle and active heart use more oxygen when there is more in the blood. The sub maxillary gland used oxygen at the same rate in all experiments, but suffocation of the animal occurred when the oxygen tension in the gland was about 40 mm. Rasmussen (see also Dubois) has shown that the oxygen concentration of the venous blood of marmots (woodchucks) is lowered during hibernation, although the oxygen capacity of the blood remains the same. This shows that the 02 tension of the blood is lowered both by fall in concentration and temperature, and this may be a factor in the lowered metabolism. The 02 concentration of the arte rial blood is not reduced, but the rate of blood-flow is very much reduced, so that less oxygen is carried to the tissues.