Page:The Zoologist, 4th series, vol 6 (1902).djvu/342

288 of the current induced by the contact of the two metals inside the insect's body was measured by means of a galvanometer; the changes in strength of the current indicated the changes of heat in the insect's body.

The book begins with an historical review of the work of naturalists on this subject since the time of Réaumur in 1734; among other names we notice that of the English naturalist Newport. The conclusion to be drawn from this earlier work is that very different results may be obtained from working at the same material; that the temperature may vary within wide bounds without prejudice to life, and that this variation of temperature is largely dependent on the temperature of the surrounding medium. But the temperature of the surrounding medium is not the only factor in determining the temperature of insects, and it is the first merit of Prof. Bachmetjew's work to have fixed and defined the other important factors which cooperate with it. He separates these factors under four heads—1, the influence of the temperature of the surrounding air; 2, influence of moisture; 3, influence of exercise; and 4, the influence of food and respiration.

The first experiments described were made with the Hawk-Moth (Deilephila euphorbiæ). It was found that at temperatures higher than 37° C. the temperature of the moth was always lower than that of the air, the greatest difference being 2·5°, when the moth was at 45·1° C. Above 48·1° the insect ceased to flutter, at 48·6° its wings sank, and at 51·4° it died. At death the temperatures of the air and of the moth were equal. These experiments were conducted in air of normal moisture, but when the air was supplied with additional vapour a different result was observed, for then the insect had a higher temperature than that of the air, and its wings did not sink until a body-temperature of 53° was reached, the air being at 49°. This effect is probably brought about by the moisture in the air preventing evaporation of the insect's juices, and so preventing cooling; while the normal metabolism of the insect naturally tends to raise the temperature. At low temperatures the temperature of the insect was always higher than that of the air. It is interesting to note, in relation to the effect of evaporation, that hairy insects tend to have a higher temperature than smooth, and this fact may