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Dr. Bashford and Messrs. Murray and Bowen. [May 30, 



maximum percentage of success is there any approach to homogeneity 

 in percentage of success on transplantation. After a time any single tumour 

 cannot be regarded as consisting of cells of equal proliferative power. Just 

 as a composite chart of all the strains propagated indicates their very 

 different behaviour at any one date, so in any single tumour at one part 

 growth is proceeding actively, at another growth is proceeding slowly or 

 actually ceases. The same heterogeneity may be postulated for sporadic 

 tumours. In all probability sporadic tumours owe their apparently con- 

 tinuous growth to the simultaneous presence in different areas of numerous 

 growing centres. These mask the effects of concomitant degeneration, and 

 account for the rarity of spontaneous absorption among sporadic as compared 

 with transplanted tumours. The greater frequency of cessation of growth 

 followed by spontaneous absorption in experimental tumours seems to be due 

 to the greater homogeneity resulting from the limited number of centres of 

 growth represented in any one implantation. 



The spontaneous absorption of the whole of a transplanted tumour is rare. 

 In the living animal it is preceded by cessation of growth. The tumour 

 apparently remains of the same size for a period of one or two weeks. 

 It gradually diminishes in size, and if examined histologically at this stage, 

 the parenchyma is found to be broken up into small masses and often 

 surrounded by a zone of large phagocytes, external to which there is an 

 overgrowth of sclerosing connective tissue. The process is indistinguishable 

 from what is frequently observed in circumscribed areas in large tumours, 

 and from that which we have described with Dr. W. Cramer* as occurring 

 when tumours disappear under the action of radium. In large tumours in 

 which growth, the cessation of growth and the tendency to absorption show 

 themselves side by side, large cysts are often encountered filled with serum 

 slightly stained with blood. The relation of spontaneous absorption to 

 a definite phase in the fluctuations in transplantability is in our experience 

 a very close one. It occurs most frequently when a high percentage of 

 success has been obtained, and coincides with the time when rapidly growing 

 tumours show a great diminution in the percentage of success on trans- 

 plantation. 



This association with a definite phase in the fluctuations has already been 

 indicated for two strains on chart fig. 4. It is additional evidence that the 

 diminished transplantability is due to a real alteration in the parenchyma 

 cells, inability to establish themselves in new animals coinciding with the 

 spontaneous cessation of growth in an animal in which growth had already 



* ' Second Scientific Eeport of Imperial Cancer Research Fund,' Part II, pp. 59 — 60. 



