In a series of previous papers (Duke-Elder, 1929) evidence has been presented that the vitreous body of the eye is an elastic protein gel in a state of high turgescence. About the physical nature of the system and the conditions which determine its stability little is known; and since these questions, in addition to being of theoretical interest from the standpoint of very dilute gels, are also of considerable moment from the practical point of view in the normal and pathological metabolism of the eye, they would seem to merit further consideration. The very small rigidity of the vitreous body, and the case with which its structure is broken down by mechanical stresses, make ordinary methods inapplicable to the study of its elastic properties. The only technique which appeared practicable was that of Freundlich and Seifriz (1923, 1924). These workers made determinations of the elasticities of a number of sols and gels by introducing a small particle of nickel into the system by a micromanipulator and needle, and attracting it by means of a suitable electromagnet; the particle was observed with a microscope, and the reversible displacements measured by means of a micrometer eye-piece. These methods were adopted with the introduction of some modifications rendered necessary in view of the peculiar nature of the vitreous body.