Mounting of Ultrathin Sections with the Aid of an Electrostatic Field

D u r i n g the d e v e l o p m e n t of n e w m e t h o d s for p re p a r i n g u l t r a t h i n sect ions of u n e m b e d d e d t issue for e lec t ron m i c r o s c o p y (1, 2, 3, 5), t h e p r o b l e m c a m e u p of p l a c i n g the sect ions o n t h e gr id. M a n y exp e r i m e n t s s h o w e d t h a t f loa t ing t h e sect ions on w a t e r cou ld resu l t in n u m e r o u s per fora t ions , t ea r ing of ce l lu la r s t ruc tu re , a n d e x t r a c t i o n of wa t e r so luble subs tances . W i t h in tense ly f ixed t issue, e.g. classical d o u b l e f ixa t ion w i t h a l d e h y d e a n d osm i u m te t roxide , these a r te fac ts were re la t ive ly ra re a n d ins igni f icant . H o w e v e r , t h e y b e c a m e ve ry p r o n o u n c e d w i t h m i l d (e.g. 2 per c e n t f o r m a l d e h y d e ) or no f ixat ion. F u r t h e r inves t iga t ions indi c a t e d t h a t the d r y t r a n s p o r t of sect ions on to the gr id cou ld e l i m i n a t e these p rob lems .