MARINE 

 BIOLOGICAL 

 LABORATORY 



LIBRARY 



WOODS HOLE, MASS. 

 W. H. 0. I. 



ON THE CUTTING OF ULTRA-THIN SECTIONS 



BY 



J. RADWAN PRAGLOWSKI 



Preliminary treatment oj pollen or spore material andjilling of 

 gelatine capsules with methacrylate 



Before embedding in methacrylate, the pollen or spore material to be 

 sectioned is successively washed in a centrifuge tube with distilled water 

 (three times), 95 per cent alcohol (tw:ice), and absolute alcohol (three 

 times). The material should remain in the last-mentioned fluid for 24 hours. 

 The alcohol is then decanted and some methacrylate (methyl methacrylate 

 one part, butyl methacrylate seven parts) is poured into the tube. (N. B. 

 Liquid methacrylate contains a stabilizer which impedes polymerization and 

 must be washed away with a two per cent NaOH solution before the meth- 

 acrylate is poured into the tube.) The methacrylate is renewed three times 

 at intervals of two hours and should be shaken, often and thoroughly, in 

 order to prevent the pollen grains from sedimenting. After the last re-filling 

 the fluid is shaken once again and transferred by means of a small suction 

 pipe to gelatine capsules (No. 3 from Parke, Davis & Co., London; see 

 Fig. 254). It is important to add a proper amount of pollen grains ot the 

 methacrylate. If too many grains are added the polymerization of the 

 methacrylate (vide postea) may be rendered more difficult. 



Polymerization in UV light 



I'he liquid methacrylate is polymerized, i.e., transferred into a solid 

 state by exposition to UV radiation; this method is to be preferred to poly- 

 merization induced by heat with the aid of a catalyzer, since the catalyzer 

 may oxidize the sporopollenine. The filled gelatine capsules are covered with 

 lids and fastened in pairs to a length of tape. About ten capsules to every 

 tape are fastened in this way and exposed to the light produced by a 120 

 watt UV lamp. The distance between the lamp and the tape should be about 



