4 LOEB— TUMOR GROWTH AND TISSUE GROWTH. [January 17, 



Our bodies consist of cells (that is small parts of protoplasm with 

 nuclear material), of products of cells of different kinds, of decom- 

 position products of cells and of material used for the building up 

 of cells. Here we are concerned with the two former only, namely, 

 with the cells and their direct products. Now growth is based upon 

 an increase in the number or the size of cells in the locality, where 

 growth takes place. The increase in the number of cells can be 

 brought about in two ways : either through the multiplication of pre- 

 existing cells, or through a wandering in of new cells. Cell-growth 

 can take place imder various conditions. If toxic substances — the 

 products of bacteria for instance — or even if inert substances foreign 

 to the body are introduced into the organism, a certain proliferation 

 of the neighboring cells and immigration of cells from the blood- 

 and lymph-vessels take place. After a certain period, such reactions 

 come to a standstill, and scar tissue develops. Such a cell-prolifera- 

 tion we do not call a true tumor ; but we class it among the inflam- 

 matory reactions. 



There are other conditions in which an unusual cell-proliferation 

 takes place in the adult organism ; in cases of wound healing. If, 

 for instance, a wound is made in the skin, the cells of the epidermis 

 proliferate until the wound is closed ; then the additional prolifera- 

 tion ceases. We call this regenerative growth. It lasts only as 

 long as the continuity of the epidermis is interrupted. This is not 

 tumor-growth. 



We now come to a third variety of cell-proliferation, distinct 

 from the two former varieties. If a follicle of the ovary ruptures 

 at the time of menstruation, the follicle cells enlarge, and proliferate 

 much more extensively than would be necessary in order to insure 

 wound-healing. There is formed a nevv' growth, which exists for 

 a limited period and then disappears. A still more striking example 

 of this new formation was found in our laboratory in the course 

 of the past year. If, at a certain period after copulation has taken 

 place, or at the period of heat, the inner surface of the uterus is 

 sufficiently exposed and cuts are made in the wall of the uterus, we 

 find that, instead of the ordinary wound-healing, another process 

 takes place, namely : the development of nodules of new tissue, 

 which resembles closely the maternal part of the placenta — without, 



