MATERIALS AND METHODS

Renal tissues from each of the four children with" familial ne-phrosis" were studied with the electron microscope. At least ten glomer-uli from each patient were examined, with the exception of case 2; only three glomeruli from this case were available. The segment of tissue obtained from each child by biopsy was cut into two pieces im-mediately upon removal. One piece was fixed in formalin and was subsequently utilized for light microscopy.'The other piece was immersed in osmic acid and prepared for electron microscopy in the following manner: Blocks of i cmm. were cut from the tissue and fixed in i per cent buffered osmium tetroxide, 21 dehydrated in graded alcohols, infiltrated and embedded in n-butyl methacrylate, 22 and sectioned in a Porter-Blum microtome23 equipped with a glass knife. 24 The sections obtained were emined in an RCA EMU-2 electron microscope, equippedwith a biased gun, intermediate lens, and io-mil condenser aperture. The objective lens had been compensated for astigmatism and contained an aperture measuring 25 to 30 P. Pictures were taken at initial magnifications of 300 to io, ooo and were en-larged photographically as desired. In addition to the ultrathin sections for electron microscopy, sections I thick were cut from tissue fixed in osmium tetroxide and embedded in methacrylate. 25 These were stained with Ehrlich's hematoxylin and studied by light microscopy. It was thus possible to study sections from the same glomerulus by both methods.