A micro-respirometer for single prepupae of Drosophila melanogaster Meigen.

IVJany workers ha,ve measured the rate of oxygen consumption of puparia of Drosophila (see Ellenby, 1945); all have worked with groups of animals. As the rate of oxygen consumption is proportional to the surface area and not to the first power of the body weight (Ellenby, 194s), the mean weight of a group of animals is an incorrect basis for the comparison of oxygen consumption. Nor is the mean weight raised to some power strictly correct, for the size composition of groups of animals will vary, and the mean weight to some power will not be equal to the mean of the individual weights to the same power. It therefore seemed desirable to investigate the oxygen the movement of a drop of manometric fluid in the capillary is measured with a microscope. The apparatus is of the differential type, the two vessels being the capillary tube and the jacket-tube; but the volume of the latter is very large in comparison with that of the former; in these circumstances the pressure change in the jacket-tube during an experiment is negligible, and the movement of the manometric fluid indicates the change of volume. The apparatus is therefore simple to use, and calibration merely involves, the determination of the volume per cm. of the capillary tube; already it has been shown that it can be readily adapted to different purposes (Waddington, Needham & Brachet, 1936; Brachet & Shapiro, 1937). Figs. 1 and 2 show the present