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: (1) 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 and 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 
