310 BIOLOGY AND ITS MAKERS 



matter around a nucleus, and the medical men prior to 1858 

 believed in free cell-formation within a matrix of secreted 

 or excreted substance. This doctrine was held with tenacity 

 especially for pathological growths. Virchow demonstrated, 

 however, that there is a continuity of living substance in all 

 growths — that cells, both in health and in disease, arise only 

 by the growth and division of previously existing living cells; 

 and to express this truth he coined the formula " omnis 

 cellula e cellula." Manifestly it was necessary to establish 

 this law of cell-succession before any idea of germinal con- 

 tinuity could prevail. Virchow' s work in this connection 

 is of undying value. 



When applied to inheritance the idea of the continuity of 

 living substance leads to making a distinction between germ- 

 cells and body-cells. This had been done before the obser- 

 vations of Virchow made their separation of great theoretical 

 value. Richard Owen, in 1849, pointed out certain differ- 

 ences between the body-cells and the germinal elements, 

 but he did not follow up the distinction which he made. 

 Haeckel's General Morphology, published in 1866, forecasts 

 the idea also, and in 1878 Jaeger made use of the phrase 

 ''continuity of the germ protoplasm." Other suggestions 

 and modifications led to the clear expression by Nussbaum, 

 about 1875, that the germinal substance was continued by 

 unbroken generations from the past, and is the particular 

 substance in which all hereditary qualities are included. 

 But the conception finds its fullest expression in the work 

 of Weismann. 



Weismann's explanation of heredity is at first sight 

 relatively simple. In reply to the question, "Why is the 

 offspring like the parent ? " he says, "Because it is composed 

 of some of the same stuff." In other words, there has been 

 unbroken germinal continuity between generations. His idea 

 of germinal continuity, i.e., unbroken continuity, through all 



