Nodal spots

A visually striking feature of Laue photographs is the existence of nodal spots (figure 7.7). Around the nodal is a blank area (Jeffery 1958). 

Figure 7.7 A predicted Laue pattern of a pea lectin crystal set with a zone axis parallel to the incident, polychromatic X-ray beam. There is a pronounced blank region in the centre of the film. The spot marked N is one example of a nodal spot.

The nodal spots lie at the intersection of curves of spots. Each curve corresponds to the intersection with the film of a cone, the surface of which contains the incident beam direction. With a flat film the intersections are conic sections. 

Figure 39-17 In situ hybridization (iSH) for the Epstein-Barr virus (EBV). ISH hybridization for EBV shows numerous positive signals (dark-blue spots) for EBV using the EBER-I probe.The tissue sample was obtained from a solid-organ transplant patient who developed widespread nodal and extranoda masses.The positive reaction for EBV In this assay supports a diagnosis of posttransplant lymphoproliferative disease. (See Color Plate 6.)...

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