. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . l-ig. 3. Locust primary spermatocyte fixed in 45 "„ isotonic acetic acid and section-stained in lanthanum nitrate. The chro- matin masses in the unstained area on the right of the section appear only as diffuse blobs, while those in the rest of the section (which is stained) show a complicated form of structure. comparison of this type has the great advantage of eliminating the effect of variations in section thicl<- ness, focussing, and photographic processing. Exper- ience has shown, however, that it is
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . l-ig. 3. Locust primary spermatocyte fixed in 45 "„ isotonic acetic acid and section-stained in lanthanum nitrate. The chro- matin masses in the unstained area on the right of the section appear only as diffuse blobs, while those in the rest of the section (which is stained) show a complicated form of structure. comparison of this type has the great advantage of eliminating the effect of variations in section thicl<- ness, focussing, and photographic processing. Exper- ience has shown, however, that it is necessary to clear the methacrylate in the stained areas of section at the same beam intensity as that used in the initial irradiation of the reference areas because the amount of clearing obtained is dependent on the beam inten- sity used. This method of obtaining unstained ref- erence areas is best applied in an electron microscope with a double condenser lens system. With the sec- ond condenser focussed to give beam cross-over in the object plane, one irradiates only a fairly sharp spot about 5 // in diameter, it has been found most convenient to move the section in such a way that this spot follows a zig-zag path across the section. In this way one obtains a reference area in all regions of the section. Staining solutions so far tried have been 2 "« un- buffered osmium tetroxide and saturated phospho- tungstic acid as genera! protein stains, and saturated ferric alum of 2 "„ lanthanum nitrate and of 2 "„ thorium nitrate as stains for chromatin. In each case positive results have been obtained. By way of control a section has been floated on distilled water instead of stain. This method of staining is particularly applicable to tissues fixed other than with osmium tetroxide. Kig. I. Locust testis fixed in 45 "o isotonic acetic acid and section-stained with osmium tetroxide. («) Stained (left) and unstained (right) regions of a section in which tl
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