The effect of molluscan glue proteins on gel mechanics.

Several molluscs have been shown to alternate between a non-adhesive trail mucus and a similar gel that forms a strong glue. The major structural difference between the two secretions is the presence of specific proteins in the adhesive mucus. The present study identifies similar proteins from the glue of the slug Arion subfuscus and the land snail Helix aspersa. To investigate the role played by these proteins in adhesion, the proteins were isolated from the adhesive mucus of different molluscs and added to commercial polymer solutions. The effect was observed qualitatively, and quantified using a dynamic rheometer. The isolated proteins triggered gelling or visible stiffening of agar, pectin and polygalacturonic acid. The effect was stronger on more negatively charged polymers. The effect of the proteins was concentration dependent with an optimal concentration of 1-1.5 mg ml(-1), and was weakened when their structure changed. Other proteins and carbohydrates found in the adhesive mucus had no clear mechanical effect on gels. These findings show that the addition of these proteins to large, anionic polymers plays a central role in the formation of a glue from a mucus-like secretion. Such a mechanism may be common among invertebrates, and it may guide biomimetic approaches in the development of glues and gels.

On the meaning of sports: cross cultural observations of super stress.

The definition of sports medicine indicates the possible therapeutic and research importance of games in the work of social scientists and clinicians. A cross-cultural comparison of super stressful competitions provides one insight into the importance of games in human societies. Fourteen such comparisons are made between Indians in Mexico who run 250-mile foot races and Americans in Alaska who conduct 1049-mile dog sled races. It is concluded that sports can help understand how a society defines itself and regulates violence. Games may be an essential "human-specific' need which provide entertainment, retain survival skills, ameliorate existential anxiety and promote religious and/or secular socialization. In this study, humans seem willing, if not insistent, to deploy considerable resources of time and material to sustain competitions among their own species, as well as between and with other species. A "sports history' is important for all individuals.