Moisture permeability of cocoon shells: Application of thermogravimetrical method to small biological samples

Desiccation tolerance is a crucial factor to survive for many terrestrial animals and plants, in particular, small animals with a large surface to volume ratio. Most terrestrial living things have any structure in their bodies to regulate the water evaporation from their bodies. In order to study the moisture permeability of small biological samples, a simple method that employs the very sensitive mass sensing and temperature control functions of a thermogravimetric analyzer has been developed. It measures the weight loss due to the water vaporization through a sample fixed on an open of a capsule containing water, resulting in the evaluation of the moisture permeability. Small tissue samples (down to about 1 mm²) can be subjected to this method. The moisture permeability of some cocoon shells has been studied with this method, which shows that it can be applied not only to the comparison among different species of silkworms but also to the comparison among the local parts of a cocoon.