[en] It is well known that the weight of some fasting insects increases when they are exposed to an atmosphere saturated with water vapour. This phenomenon is generally considered to be due to the absorption of moisture from the air, and the insects concerned, such as Leptino-tarsa1, Chortophaga2,3, Cimex4 and Tenebrio (larvæ)5 are often called 'hygroscopic'. The weight change is obviously influenced by a series of factors. In order to isolate the factor of 'hygroscopicity', we have kept the insects in air saturated with water vapour, the vapour being derived from water containing 8 percent of heavy water ; the vapour also contains 8 percent of heavy water. The concentration of heavy water in the insects was determined after various exposures to this vapour by the method of Linderstrom-Lang
