The study of cell life and metabolism in the living human eye has great possibilities, but direct observation of the reactions of cells can be made only with the lower magnifications. Even this has proved a great boon, as accomplished with the aid of the slit-lamp microscope. Much has been learned through studies of histology and pathology. Much more remains to be learned of the complex chemical relations existing in the cells and the humors of the eye by working with living material in vitro.
The crystalline lens seems to be particularly adapted to in vitro experiments, because, of all the tissues of the body, the conditions surrounding it in vivo most closely simulate those which may be produced in vitro. Suspended as it is between the aqueous and vitreous, it is dependent for its nutrition not on the direct circulation of blood but on a process of endosmosis,