Immersion of the intestinal tissue, from rat jejunum, in hypertonic saline produced very rapid changes in all regions of the epithelial cells, but the apical region was apparently unaffected by hypotonic solutions for at least ½ hour. In both cases, blistering of the microvilli was taken as the first sign of degenerative changes which finally resulted in a breakdown to large vesicular particles. Consideration of both normal and modified tissue indicates that the core of the microvillus contains either paired strands or tubular structures. Lateral cross-fibres extended from the core to the microvillus membrane and may be an essential part of the supporting structure of the microvillus. Densitometer traces across the microvillus membrane at various stages of modification indicated that this membrane might include a 75 A unit membrane structure with additional components associated at either surface. Interruptions in the membrane were apparently expanded by the hypotonic solutions and these might possibly be distinguished from preparative artefacts.

As part of a general study of the effects of various ions on the low-angle x-ray diffraction patterns of nerve myelin, specimens were immersed in aqueous media containing ions in the proportions recommended for Ringer's solution but at hypertonic and hypotonic strengths. Observations were made which may have great significance in relation to the role of ions and of water in myelin structure. Materials and MethodsOnly data on the frog sciatic nerve are reported in this paper. Segments of nerve trunk were immersed in ionic media for various lengths of time and then mounted in thin walled glass capillary tubes for examination by x-ray diffraction using high resolution low-angle cameras (1) and Cu K,* radiation. After preliminary experiments, studies were concentrated on specimens which had been immersed in normal (N), hypertonic (10 N), and hypotonlc (N/4) Ringer's solutions, 0.25, 0.9, and 10 per cent saline, and Ringer's solution in which the Ca ++ concentration alone had been increased to 10 1,;. After examination by x-ray diffraction, the specimens were either dried and reexamined later, or immersed in normal Ringer's solution and reexamined after a further 16 to 24 hours. RESULTSThe most interesting low-angle diffraction patterns were those obtained after 20 to 24 hours in 10 ~ and ~/4 Ringer's solutions. Photometer traces of such patterns, together with a trace obtained from nerve immersed in normal strength Ringer's solution, are shown in Fig. 1. The 270 A band from the N/4 specimen can be seen to be clearly resolved in the original diffraction patterns but the photometer fails to resolve it to more than a marked shoulder in the trace.The detailed changes of diffraction pattern resulting from immersion of the nerve specimens in hypertonic and hypotonic solutions will be described separately. Hypertonie Solutions:In the early stage of modification of myelin structure by 10 N Ringer's solution there is an apparent strengthening of the third order x-ray reflection 89

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A low angle X-ray diffraction study of three homologous series of phospholipids has indicated the existence of three thermally related polymorphic forms. The layer spacings of these compounds decrease markedly (usually in well-defined steps) with rise in temperature, and an attempt has been made to account for these changes in some detail in terms of a tilting of the long chain molecules within the layers as a result of modifications of the balance between inter-molecular van der Waals' and ionic forces.

SUMMARY The usual simple methods for the preparation of soft tissues for scanning electron microscopy failed to demonstrate the presence of microvilli on intestinal epithelial cells from rats. Treatment with a mucolytic agent or surface‐section methods also failed. However, the isolation of the brush borders as the first step in the preparatory procedure did allow a study of the microvilli. The width and height of the microvilli differed from those seen by transmission microscopy and it is suggested that these differences are related to both the shadow‐material used and the presence of a mucopolysaccharide on the surface of the membrane. The technique illustrates the possible use of fractionation methods as part of the preparative procedures in scanning electron microscopy.