ii2 SCIENCE PROGRESS 



three cells must often be driven further from the bulk, be 

 scattered, in fact, and give rise to smaller tumours which become 

 noticeable later than the main tumour. It is remarkable that 

 practically all these secondary growths have been in the lungs, 

 though secondary growths in the lungs do not occur in the 

 ordinary course of primary carcinoma. These grafts have 

 always, in my experience, been enclosed in a definite capsule. 

 On following the sequence of events trom a few hours after 

 grafting up to fourteen days, at first at intervals of twelve hours 

 and subsequently of twenty-four hours, I found that the in- 

 flammatory reaction in the surrounding tissues of the mouse 

 began almost at once : whilst not a single tumour cell which 

 had been introduced into the animal showed any sign of multi- 

 plication until twenty- four hours after grafting, the inflammatory 

 products had by this time completely surrounded the graft. 

 Long before the cells of the graft had begun to multiply 

 actively, the inflammatory reaction had already cut them off 

 effectually from the surrounding tissues. The inflammation 

 was always in advance of the proliferation of the tumour cells. 

 This accounts for the rarity of metastases. I have but once 

 personally observed one in the many thousands of inoculated 

 mice I have examined except in those infected with emulsions 

 of tumour cells. 



One of the most characteristic features ol primary malignant 

 growths is that when they are well established and have reached 

 a considerable size, their removal by operation is almost in- 

 variably followed by recurrence. Operations are completely suc- 

 cessful only when performed at an early stage. An operation is 

 often desirable in order to prolong life and to avoid unnecessary 

 suffering, when there is practically no chance of a complete cure. 

 With the graftable tumours in mice and rats, however, the case 

 is very different. 1 have just completed a series ot experiments 

 in which I have removed tumours from mice and rats. These 

 were in every instance large and well-established growths, in many 

 cases approaching in size that of the body of the animal from 

 which they were removed. 1 In only eleven cases out of forty- 

 four has the tumour recurred and in these a second operation 



1 In about 8o per cent, of the mice the peritoneum was involved and the 

 operation often included an incision in the peritoneum from the ribs to the pelvis, 

 besides the removal of a considerable portion of it. The two mouse tumours used 

 were of a particularly virulent kind. 



