4 SCIENCE PROGRESS 



differentiated the disease from infections. Thiersch, Waldeyer, 

 and others finally established the relation of cancer to normal 

 tissues, and its probable origin from them in many cases, in 

 opposition to the humoral theories which found their last expo- 

 nent in the distinguished Virchow. 



Experiments like Langenbeck's were repeated with great 

 perseverance even up to the present decennium ; but, with 

 the development of bacteriology, they were modified in many 

 instances, where the experimenter believed he had discovered 

 the " virus " or other minute parasitic cause of the human 

 tumours. Whereas many observers were unable to induce 

 cancer in animals in those ways, others claimed success. 

 Criticism always effectively disposed of those claims. The 

 tumours produced in animals bore vague, or even only imagi- 

 nary, resemblances to the tissues of the human tumours 

 employed in the experiments. Many were proliferations of 

 the inflamed tissues of the animals themselves, as the result 

 of the experimental inoculations, while others were normal 

 and pathological structures encountered in animals, but not 

 in man, and entirely independent of the experiments. 



All this time descriptive pathology and study at the bed- 

 side were advancing knowledge, leading ultimately to the 

 accumulation of an overwhelming amount of evidence in 

 favour of conclusions in two directions : (i) the cancerous 

 tissues destroyed life mainly, if not solely, by their powers 

 of progressive proliferation and of dissemination in the body : 

 (2) the proliferation arose primarily in a circumscribed area, 

 and proceeded from causes inherent in the growing cells them- 

 selves. It required many years before the early surgical 

 treatment of the disease ousted all other methods, and was 

 acknowledged to be justified absolutely by increasing certainty 

 of the circumscribed origin of cancer. This had been clearly 

 enunciated by Wilks as a result of investigations pursued 

 between 1847 an d 1868, and was stoutly defended by Campbell de 

 Morgan and Charles Moore, against the constitutional views 

 of the disease ably expounded by Paget and his followers. 

 The opposing schools joined issue in a memorable debate 

 before the Pathological Society of London in 1874. The 

 methods of descriptive pathology and of clinical study ulti- 

 mately reached their limitations, for they were inadequate to 

 explain the powers of growth, which they had sufficed to 



