io SCIENCE PROGRESS 



origin of cancer, it is unnecessary for growth to continue. 

 (3) The conditions of the origin of cancer were to be sharply 

 distinguished from those of continued growth. (4) The pro- 

 gressive, apparently vegetative, growth was to be explained 

 as inherent in the cancer cells without the assumption of the 

 stimulus of extraneous agents. The amount of growth pre- 

 sented a cell problem of importance in itself and required to 

 be further analysed. (5) The purely cell problems of cancer 

 required to be attacked by the methods of experimental and 

 comparative biology rather than from the narrower standpoint 

 of human pathology. 



Those conclusions would have been illegitimate if drawn 

 only from experiment at that time. They were advanced 

 also on the basis of a comparative study of the disease in the 

 vertebrates down to marine teleostean fishes living in a state 

 of nature, and after careful statistical studies of the national 

 mortality from cancer, and of its occurrence in the patients of 

 London hospitals. The zoological distribution of cancer made 

 it obvious that it developed in man, independently of any direct 

 influence proceeding from civilisation, diet, or other one of many 

 inconstant external factors. Subsequent studies in the same 

 direction, and also into the ethnological distribution of the 

 disease, have but rendered this inference more justified. The 

 disease has been found in all those races of mankind among 

 whom diligent search has been made. Where it was said 

 to be rare it has been found to be common — e.g. in Japan 

 some 25,000 deaths are annually recorded from cancer. Where 

 it was said to be absent it certainly occurs. Of course, no 

 comparison or statement of relative frequency is possible 

 between civilised and aboriginal man, and between tame and 

 wild animals. The fact of prime importance is that the disease 

 is of universal occurrence, pervading all forms of vertebrate 

 life, and everywhere adapting itself to the conditions presented 

 by different species. The disease is universal, but the difficulty 

 of transferring it even to individuals of the same species is 

 unique, and when successful is not to be confounded with 

 the production of cancer ab initio. 



Throughout the entire distribution of the disease two facts 

 stand out prominently : The number of cases recorded is in 

 direct proportion to the care with which it is possible to make 

 examinations, and to the number of adult and aged individuals 



