Within a very short time we have witnessed the method of research in the problems of malignant growth, which was limited almost entirely to histologic and statistical studies, changed to an experimental method that is fairly comparable with those of bacteriology. The discovery that many spontaneous tumors in the lower animals are capable of successful transplantation from one animal to another of the same species has made it possible to follow out careful cultural methods, in which the chief difficulty is the limited variety of culture media on which the tumors can be made to grow, namely, the bodies of animals of the same species as the host of the original tumor.
The first important experiments of this sort were those of Hanau, later followed by Leo Loeb and M. Herzog in this country, and by Jensen, Borrel and Michaelis abroad. In Ehrlich's laboratory in Frankfort, besides the well-known work