1. The rate of loss of weight of adult male Blatta orientalis was measured in half-saturated and in dry air at various temperatures from 20 to 40° C. 2. The rate of consumption of oxygen was measured in saturated air over the same temperature range. 3. If no correction is made for losses of weight other than water loss, the rate of total loss can be taken as a satisfactory measure of the rate of water loss. 4. At different temperatures the rate of water loss was not proportional to the saturation deficiency of the air. The rate of loss in dry air was proportionally too low (or the rate at higher temperatures too high) to fit this relationship. 5. A formula was found for the rate of loss at all temperatures from 20 to 30° C, and the conclusion was reached that most of the water escapes through the spiracles rather than from the body surface. 6. Above 30° C. the rate of loss is much greater, due to a change of respiratory mechanism from diffusion regulation to ventilation regulation. 7. Blatta orientalis dies from heat stroke at a minimum temperature between 36 and 40° C. It will die from desiccation at any of the temperatures and humidities studied, but the speed of desiccation increases very rapidly above 30° C. owing to the form and mode of action of the tracheal system. Desiccation sets an upper limit to the temperature range of the species, which is below the heat-stroke temperature. 8. The view that the temperature range of the species is increased by a regulation of body temperature through a rapid loss of water vapour is untenable.
D. L. Gunn
The Journal of Experimental Biology