1904.] On the Zoological Distribution, etc., of Cancer. 71 



remain of normal appearance, and these gradually increase in number. 

 In the earliest transplantations mitotic division is absent, and it is not 

 till later, when a considerable mass has arisen, that mitoses appear. The 

 earliest mitoses we have been able to observe have been of the somatic 

 type. 



Transplantation is, in fact, identical with the process of metastasis 

 as it occurs in the individual providing the tumour. It is remarkable, 

 however, that the tumour of Jensen's experiments does not produce 

 metastases naturally, and its malignancy is only evidenced by its 

 progressive growth, and the undifferentiated character of the cells. 

 The process is in no sense an infection, the tissues of the new host not 

 participating in the formation of the new parenchyma. In this 

 interpretation we are in agreement with Jensen and differ from 

 Borrel, who conceives the results to be due to the agency of a virus 

 cancdreux. 



The origin of the stroma has not been accurately determined. The 

 power of growth of this tumour is remarkable. In every mouse 

 in which the transplantation succeeds, the new growth may attain a 

 weight equal to that of the animal itself, and over 400 such trans- 

 missions have been effected by Jensen in Copenhagen and the Cancer 

 Research Fund in London. A mass of tumour, 16 lbs. in weight, has 

 thus actually arisen from the original one, and that without participa 

 tion of the cells of the various hosts and without manifest change 

 in structure. This great power of growth is a phenomenon un- 

 paralleled in the mammalia, and indicates the potentialities in cases 

 in which widespread dissemination has occurred before death in a 

 human patient. 



The experimental transmission of carcinoma shows that we must 

 distinguish between the problem of the genesis of a malignant new 

 growth, and that of the conditions which permit of its continued 

 existence. While the conditions leading to the initiation of malignant 

 tumours are relatively infrequent, we have examined upwards of 

 1000 tame mice, and have discovered two with cancer ; once begun, 

 this proliferative activity can, under favourable conditions, persist for 

 a long time unaltered, and can give rise to masses of tissue of great 

 size, having no relation to the restrictions which limit the growth 

 of adult organisms in a large proportion of healthy animals. 



The phenomena of cell division, indicating a similarity to the 

 normal reproductive tissues, may help to explain the nature of this 

 great power of multiplication, but leave the problem of cancer genesis 

 practically untouched. They give, however, important indications of 

 the character of the processes on whose elucidation the solution of the 

 question depends. The wide zoological distribution of malignant new 

 growths — its limits are not yet determined — indicates that the cause 

 of cancer is to be sought in a disturbance of those phenomena of 



