Relaxation of Snails before Fixation

Abstract

NUMEROUS narcotizing agents have been used for relaxing snails, and among the more important of these employed recently are menthol and nembutal^1,2,4. Menthol has been reported as giving variable results⁴; some snails become well extended, but others contract when this agent is used. This variation in results is observed especially when larger freshwater snails (shell height 15–25 mm.) such as Lymnaea palustris and Physa gyrina are placed in water to which menthol crystals have been added. On the other hand, smaller lymnseids such as L. humilis (maximum shell height, 12 mm.) relax well with menthol³. Nembutal gives good results with Pomatiopsis lapidaria and P. cincinnatiensis ⁴, but, like menthol, is unsatisfactory for the much larger L. palustris. This snail will contract slowly over a period of 4–5 min. when placed in 10 per cent formaldehyde even after being in rather high concentrations of nembutal (5 ml. stock veterinary nembutal in 150 ml. water at 4° C. for more than 40 hr.). Using this concentration of nembutal at room temperature results in contraction of L. palustris before it is properly narcotized, so that it is unsuitable for fixation. The same result occurs with snails in higher concentrations of nembutal (10 ml. in 150 ml. water) at 4°C.