THEORIES AND PROBLEMS OF CANCER 109 



whether or not, when a group of these bacteria has multiplied 

 beyond the limit necessary to the imitation of one cell, the 

 process of cell division (mitosis) is imitated as the image of a 

 second cell is formed, which would be necessary as mitoses 

 are particularly numerous in many cancers. It is difficult to see 

 how evolution or any other process could have brought about 

 a case of mimicry which could only have been observed by 

 the individuals attacked by the organism since the invention 

 of the modern microscope. Mimicry which protects or other- 

 wise benefits the mimic can be understood. Mimicry such as 

 this is inconceivable. Various micro-organisms are frequently 

 found in cancer but these are found also in other diseased con- 

 ditions and they are not always present in cancer. 



Experimental Investigations 



During the past ten years a very large number of experi- 

 ments have been carried out with carcinomata occurring in 

 mice. One reason for this has been that some of these tumours 

 have been found to be transmissible — that is to say, on trans- 

 plantation from one mouse to another they grow in the new 

 hosts in a variable proportion of cases, the proportion of suc- 

 cessful transplantations being dependent upon several different 

 conditions. 



An impression seems to exist that the present activity in 

 this particular branch of experimental work followed immedi- 

 ately upon the discovery that tumours could be transplanted. 

 This is not a correct impression. The activity is due to the 

 fact that public interest in cancer research took a practical turn 

 about ten or twelve years ago and that means were provided 

 for experimental work. 



The first successful attempt to transplant a malignant tumour 

 from one individual to another appears to have been that made 

 by Novinsky, who transferred a cancer occurring in the nose 

 of a dog into two other dogs. 1 He was followed by Wehr 2 

 and by Hanau, 3 the former transplanting a sarcoma occurring in 

 a dog, the latter an epithelioma occurring in a rat. Morau, 4 

 several years later, successfully transplanted a carcinoma in 



1 Centralbl.f. d. Med. Wissensch. Berl. 1876, xiv. 790. 



2 Arch.f. klin. Chir. Berl. 1889, xxxix. 226. 



3 Ibid. 1889, xxxix. 678. 



4 Arch, de Med. Exper. et dAnat. Path. Paris, 1894, vi. 677. 



