Chapter $ 

 Tumor Growth and Organismal Differentials 



In the preceding chapters the principal facts concerning the significance of 

 organismal differentials for the growth of transplanted tumors have been 

 analyzed. The concept of organismal differentials has contributed in 

 various ways to the understanding of tumor transplantation and of the im- 

 munity against transplanted tumors; and conversely, the analysis of tumor 

 growth has contributed to the understanding of the organismal differentials. 

 It is for these reasons that we have discussed also the various factors which 

 interact with the organismal differentials in tumor growth. In concluding, it 

 will be of interest to trace the development of the various concepts and theories 

 relating to the factors which are of importance in the transplantation of 

 tumors. Some of the most prominent investigators in the field of cancer have 

 contributed to these studies, and while certain of their interpretations have 

 been modified in the course of time, the conclusions they expressed and the 

 experiments they carried out in support of them helped greatly to advance our 

 knowledge of the nature of cancer and of the factors active in transplantation. 



Jensen in his transplantations of mouse carcinoma approached the facts he 

 discovered from the point of view of the bacteriologist and immunologist. 

 It had been found possible to induce immunity against various diseases caused 

 by microorganisms. By using as a vaccine, in a weakened form or in a very 

 small quantity, the microorganisms that caused the disease or certain of their 

 derivatives, or by introducing related organisms less virulent for the host but 

 sufficiently related to the causative agent, an active immunity was produced. 

 These studies gave direction to and supplied the problems for Jensen's work 

 as well as for the following investigations of Ehrlich and Apolant, and also 

 of Bashford, Murray, Haaland, Russell and Cramer. In the beginning it was 

 assumed that cancer cells differ in various ways from ordinary tissue cells 

 and that the laws relating to the transplantation of tumors differ in some 

 essential respects from those governing ordinary tissue cells. Thus Ehrlich 

 applied the same principles in explaining immunity against cancer and im- 

 munity against microorganisms ; he explained both on the basis of his nutri- 

 ceptor and athrepsia concepts. However, Bashford and his associates, Murray, 

 Russell and Cramer, soon recognized important differences between these two 

 types of immunity, and one of the most essential was the fact that a formation 

 of antibodies against the ordinary transplantable tumor could not be demon- 

 strated in the case of tumor immunity; they substituted therefore the term 

 "resistance" for that of "immunity." But even these investigators considered 

 the problem of immunity or induced resistance against tumor growth as the 

 principal problem of tumor growth. 



Although soon some facts were established, which proved certain similari- 

 ties between the behavior of tumors and of normal tissues, still the immunity 



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