An X-ray and electron microscope study of tropomyosin.

A technique that we have found convenient in trying to obtain oriented preparations of elongated macromolecules is to make a thin film by drying a pool of sol on a glass plate, and then to stretch narrow ribbons of tie film (Astbury & Dickinson, 1940). The first step tends to leave the molecules lying parallel to the surface of the film but in all azimuths, while the second tends to draw them parallel also to the direction of stretching, so that in the end an X-ray fibre diagram should result. Even without the second step, how- ever, an imperfect fibre diagram may be expected if the specimen is photographed with the X-ray beam parallel to the surface of the film. Further orientation and stretching effects may be produced by squeezing the ifim between small pieces of plate glass clamped together by screw clips.