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Abstract

In th e o rd in ary m eth o d s of te stin g m olluscicides in th e lab o rato ry each group of snails, usually 10, is placed in a glass or plastic Container in to w hich a c e rta in concentration of th e chem ical h a s b een introduced. T he n u m b e r of co n ta in e rs corresponds to th e n u m b er of co n cen tratio n s required in each te s t.Replications of th e te sts are usually n ecessary in o rd er to increase th e n u m b er of snails in each ex p erim en t. In doing th a t, additienal co n tain ers are required.A common a n d im p o rta t e rro r in m ollusciciding lab o rato ry ex p erim en ts resu lts from the tend en cy of th e snails to craw l out of the toxic solutions in to w hich th ey have been im m ersed. As fa r as th e experience of th e a u th o rs cif th e c u rre n t p a p e r is concerned th e re is no p erfect device completely able to p rev en t th e escape of the snails from th e m olluscicide.In th e technique described in th e p resent paper th e e rro r m e n tic n e d above is eliminated an d th e n u m b e r of co n tain ers can be greatly reduced. Description o f th e techniqueA large glass Container is used for each chemical c o n c e n tra tio n . T he volum e of th e C ontainer will depend on th e num ber of sn ails to be tested in each chem ical c o n c e n tratio n . K eeping th e proportion of 100 m l o f th e m olluscicide solution per snails, a -Container holding five liters will receive 50 snails.A fter filling th e containers, (one for each co n ce n tra tio n of th e m olluscicide to be te ste d ), th e snails c an be introduced. G roups of 10 sn ails are placed inside bags of nylon n e t (m esh 1.5 m m diam eter) an d th e n plunged in to th e solutions. F or la rger snails th e groups w ith in each bag can be sm aller. T he n u m b er of bags to be placed in each Container will depend on th e volum e of th e liquid. In th e experim en ts m ade in th is lab o rato ry five bags were used (to talin g 50 snails) for each c o n c e n tratio n of th e chem ical. E ach bag is tied w ith a th re a d w hich bears a n Id en t ificatio n ta g on its free end (Figs. 1 an d ).T h e kind of n e t utilized is lig h t enough to p e rm it th e bags to flo at in th e solution. T he snails are seen inside th e bag com ing u p to th e surface to b re a th ( fig. 3 ).A fter th e exposure period, th e bags are ta k e n o u t of th e molluscicide, opened, an d th e sn ails are w ashed a n d tra n sfe rre d to tfresh w a te r. Bags are used only once.School of Medicine, U niversity of Pernam buco and Centro de P esquisas Aggeu M agalhães, Reci fe, Brazil.