Effects of dehydration and rehydration on Periplaneta americana

Abstract

This study describes the effects of dehydration and rehydration on the cockroach. Osmolality and Na and K content of various body fluids have been measured. The haemolymph osmolality increases only slightly during 9 days of dehydration, although there is a 15 to 22 per cent weight loss and a decrease in haemolymph volume. During dehydration NaCl and other solutes are removed from the haemolymph. A cannulation technique was used to collect the fluid secreted by the Malpighian tubules in vivo. The tubules continue to secrete at a slow rate even after 8 days of dehydration. Although the tubules can remove the excess solutes from the haemolymph during dehydration, analyses of faecal pellets show that the excess NaCl is not excreted. After a dehydrated animal is given only water and no food, there is a rapid increase in haemolymph volume but only a slight decrease in haemolymph osmolality. The source of solutes used to form new haemolymph is not known.