Tissue Growth and Tumor Growth’

Tumors in general and cancers in particular are tissues growing under special conditions. A comparison between the laws determining tumor and tissue growth will deepen our knowledge of the physiology of tumors as well as of tissues. There exist similarities and analogies in the behavior of both, and there are differences either real or due to a gap in our knowledge. The differences will suggest new problems. In this brief r6sum6 no attempt at completeness will be made, and we will have to be content with mentioning some of the salient points. We shall first compare the causes of tumor and tissue growth, then the reactions of the host organism against tumor and tissue growth, and lastly, certain phenomena observed primarily in the tumor cells. We will have to inquire how far the last mentioned phenomena are duplicated in tissue growth. 1. Tissue growth is initiated by external factors affecting a more or less complicated system and leading to chains of reaction which may be identical, or at least similar, even in ‘cases in which the primary causes differ. These primary causes are called “formative stimuli’’ in order to distinguish them from functional stimuli. It is probable that essentially both kinds of stimuli are identical and act in a similar manner. The difference in the result of both kinds of stimulation depends probably on the quantitative differences in strength and time, and on the differences in the systems on which they act. 2. The primary causes initiating tissue growth may be either