THE STUDY OF CANCER 5 



define as embodying the essential problem of cancer. So 

 distinguished an observer as Campbell de Morgan confessed 

 that "experiment fails us, and we know nothing of the earliest 

 stages of the disease." The search for a specific cancer cell 

 proved futile, according to Wilks, as early as 1868. Investi- 

 gation of the minute intra-cellular structures provoked much 

 controversy during the last twenty years of the nineteenth 

 century, but remained, as it remains to-day, barren of positive 

 results. Discussion of the infective or non-infective nature of 

 cancer became entirely hypothetical. All attempts to induce 

 cancer in animals by inoculation from the human subject 

 having led to negative results, the method had been practically 

 abandoned. Efforts to elicit experimentally the hypothetical 

 (latent) powers of growth of embryonic tissue in support of 

 Cohnheim's hypothesis, or those of groups of adult cells whose 

 " organic continuity " with the tissues was dissolved, as postu- 

 lated by Ribbert, showed how limited were the powers of 

 growth of embryonic and adult tissue. In the case of embryonic 

 tissues they showed also that the ultimate cessation of growth 

 was accompanied by a differentiation into tissue of adult type. 



The acquisition of new knowledge seemed very remote indeed. 

 In spite of the most discouraging outlook, courageous and serious 

 resort to experiment had become a pressing necessity at the end 

 of the nineteenth century, and, fortunately, the success attending 

 subsequent experiments has conferred a positive value on much 

 of the apparently negative experimentation described above. 



The study of the phenomena called forth by inoculating the 

 tissues of animals into others of the same, and of alien species, 

 showed during the closing years of the last century how distinct 

 — chemically and biologically— the tissues of one species of 

 animal are from those of another, even when nearly allied and 

 elaborating their tissues from identical pabulum. The demon- 

 stration of the difference appears to have re-directed attention 

 to a few earlier experiments on the transmission of tumours 

 from one animal to others of the same species. Statements of 

 the success attending the deliberate inoculation of human beings 

 with portions of their own cancerous tumours were remem- 

 bered. Observations made by Hanau, Jenny, Morau were 

 remembered as indicating the transference of the disease from 

 rats and mice to others of the same species. 



It was by no means clear how those experiments were to be 



