70 ORGANISMS OF ONE CELL 



which they belong. Thus epithelial cells of the mouse, under 

 abnormal conditions which we call cancer, may be transplanted 

 from mouse to mouse for years after the normal length of 

 life of the original animal, a fact demonstrating that epi- 

 thelial cells, at least under these abnormal conditions, have 

 a far greater potential of vitality than is represented by 

 the ordinary length of life of the individual. Weakness and 

 death of the individual cells, therefore, must be due to some de- 

 fect in the inter-relations of the many differentiated cells and 

 organs of the body of the metazoon; this defect is cumulative 

 until the organisms are unable to carry on the necessary 

 functions, and die. The same result may be brought about by 

 the local destruction of cells through disease; thus bacteria 

 may destroy the cells of the lungs in pulmonary tuberculosis, 

 a loss resulting in the weakening of other cells in the body, and 

 finally in death through inability to obtain oxygen and gives off 

 C0 2 . 



This gradual weakening of the cells and vital activities in 

 general led Weismann, a famous German biologist, to the con- 

 clusion that old age and natural death are penalties which the 

 higher organisms must pay for their privilege of differentiation, 

 while the unicellular organisms, dependent only upon themselves, 

 have an unlimited capacity of life, i.e., are potentially immortal. 

 These conclusions have been repeatedly challenged on the 

 ground that all protoplasm is subject to the same laws of 

 physiological usury, and numerous experiments beginning 

 with those of Maupas, 1888, have been undertaken to show that 

 protozoa, like metazoa, undergo senescence, and die from old 

 age. It follows from the negation of spontaneous generation, 

 however, that all living things are composed of protoplasm that 

 has been living continuously since life appeared on the earth, and 

 it is obvious that all organisms contain some cells endowed with 

 the potential of physical immortality. These, called the germ 

 cells, hand down the race from generation to generation. The 

 experiments of Maupas and of subsequent investigators have 

 shown that it is only in this sense that protozoa are physically im- 

 mortal. Maupas isolated Oxytricha, Stylonychia, and other 



