CANCER RESEARCH 19 



doubtful whether it ever disappears spontaneously. It is therefore a 

 disease which leads without special interference to the death of the 

 patient, sometimes very soon, sometimes many years after the first 

 symptoms appear, according to the rapidity of the growth of the cancer. 

 The characteristic feature of cancer as a disease may therefore be stated 

 as follows : Cancer consists in an abnormal multiplication of cells at a 

 certain, at first, usually well-defined place of the body. All the deleteri- 

 ous results are primarily produced through this continuous growth 

 which spreads into different parts of the body. This growth as such 

 through the pressure it exerts on neighboring organs or through its 

 infiltration into and destruction of vital parts of the body leads to the 

 death of the affected individual, secondarily toxic influences may be 

 added to the primary results of the growth; but these toxic influences 

 are as far as we know not of a specific character. It is different in the 

 so-called infectious diseases. There the disease consists primarily in an 

 intoxication by products given off by the invading organisms and a pro- 

 liferation of the body cells plays only a subordinate role in the disease 

 process. 



While we can thus, in a rough way, define and differentiate cancer 

 from certain other diseases, we must be well aware of the fact that a 

 complete and satisfactory definition of a process can be given only after 

 the completion of its scientific analysis. Usually, however, definitions 

 are given in the beginning of the study of a certain process; and they 

 have therefore only a provisional value. Certain apparent, often super- 

 ficial features are at first used for characterization. During the 

 progress of scientific investigation new relationships to neighboring 

 fields are discovered, differences which at first appeared to be of a quali- 

 tative are gradually to be found to be merely of a quantitative character. 

 Thus we must prepare for the eventuality that the sharp differentiation 

 between cancer and infectious or toxic diseases may not be upheld 

 through future investigations. In fact already at the present time we 

 know of conditions which seem to be intermediate between the two sets 

 of phenomena and it is probable that we will gradually have to add cer- 

 tain subdivisions defining conditions which have factors in common 

 both with cancer and the so-called infectious diseases. At present it is 

 of comparatively little importance to discuss whether certain inter- 

 mediate phenomena are to be classed as cancer or infectious disease, 

 while it is of the greatest importance to describe and analyze the char- 

 acter of these intermediate phenomena. In a similar manner, it is of 

 relatively slight importance to justify or deny the admissibility of call- 

 ing certain processes in animals and plants cancer — the definition of 

 cancer necessarily being a provisional one — while it is of the greatest 

 importance to discover similarities between certain tumor-like condi- 

 tions in man, animals and plants. 



