Until a few years ago, it was assumed that the life and development of tissues and their constituent cells are bound up with the body as a whole. Body cells had not been "cultivated" in vitro in the way that has become familiar in the growth of micro-organisms of various sorts. The pioneer experiments of Harrison1 showed the possibility of cultivating tissues outside of the body by the demonstration that embryonic tissue of the frog, transplanted into coagulable lymph, will develop normally. Subsequently Carrel and Burrows2 succeeded in cultivating outside of the body adult tissues of mammals. These possibilities have since been demonstrated repeatedly by various investigators in different parts of the world. Not only normal but also malignant tissues have thus been grown in culture.
At first, before the experimental technic was developed to its present stage of perfection, the life of the tissue cultures outside of