172 LEO LOEB. 



INDIVIDUALITY DIFFERENTIAL AND POTENTIAL IMMORTALITY OF 



SOMATIC CELLS. 



The fact that certain tumors can withstand the action of the 

 homoiotoxins has a still wider bearing. We must remember that 

 common transplantable tumors are the direct descendants of ordi- 

 nary tissue cells, such as we normally find in the individuals of 

 the particular species which we use. The tumors may be derived 

 from a variety of normal tissues and in general the transforma- 

 tion from normal cells into tumor cells takes place under the in- 

 fluence of a long continued action of various factors enhancing 

 growth. Tumor cells are therefore merely somatic cells which 

 have gained an increased growth energy and at the same time 

 somehow gained, in some cases, the power to escape the destruc- 

 tive consequences of homoiotoxins. This ability of certain tumors 

 to grow in other individuals of the same species has enabled us to 

 prove through apparently endless propagation of these tumor 

 cells in other individuals that ordinary somatic cells possess the 

 potential immortality in the same sense in which protozoa and 

 germ cells possess immortality. Thus tumor transplantation 

 made possible the establishment of a fact of great biological in- 

 terest which because of the homoiosensitiveness of normal tissues, 

 could not be shown in the latter. 



We wish, however, especially to emphasize the fact that our 

 experiments did not merely prove the immortality of tumor cells, 

 but of the ordinary tissue cells as well, the large majority or all 

 of which can be transformed into tumor cells. At an early stage 

 of our investigations we drew, therefore, on the basis of these 

 experiments, the conclusion that ordinary tissue cells are poten- 

 tially immortal ; notwithstanding the fact that especially under 

 Weismann's influence the opposite view had been generally ac- 



other. I have referred to this distinction in this paper ; I have also empha- 

 sized how unsuitable transplantable tumors are for the analysis of individ- 

 uality differentials. In my previous papers I have discussed the influence of 

 such adventitious factors as sex, age and pregnancy on the individuality dif- 

 ferentials, and showed that within the limits of our experiments such factors 

 do not noticeably influence the individuality reaction ; this applies to guinea 

 pigs above the age of four weeks, as far as the age factor is concerned. We 

 also referred to the apparently abnormal behavior of tissues of the child trans- 

 planted to the mother. The factors that are responsible for this peculiarity 

 need, as I stated above, further investigation. 



