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



transplanted in each animal varied between O01 and - 02 gramme.* The 

 pieces were selected from the whole tumour, and hence their behaviour 

 furnishes an estimate of the proliferative energy of its component parts. The 

 use of a restricted number of random fragments is rendered necessary, because 

 it is impossible to transplant the whole of every tumour ; the number of 

 animals required of itself limits the investigation. 



The method of experimental propagation by implanting minute cellular 

 grafts leads to a progressive subdivision of the parenchyma, and to the 

 distribution over a large number of animals of the descendants of cells 

 previously associated together in one animal. The experimental tumours 

 consist of a parenchyma arranged in alveoli. The study of the early stages 

 after transplantation shows that, at first, single alveoli constitute separate 

 centres of growth, and we may therefore term them the " parent alveoli " of 

 the tumour. Since the cells of different alveoli do not intermingle, the 

 progeny of the discrete growing centres in the transplanted tissue remain 

 separate, and are further separated from one another as the parent alveoli 

 increase in size and bud off daughter alveoli at the surface. When minute 

 portions of such a tumour containing very numerous daughter alveoli are in 

 turn transplanted it is very improbable that any one fragment will contain 

 cells from each parent alveolus, i.e., progeny of all the primary growing 

 centres in the cellular graft which gave rise to the tumour. On the contrary, 

 such a fragment is likely to contain cells closely related to one another, i.e., 

 from only one of the new growing centres of which the tumour is ultimately 

 composed. Thus, in the course of repeated implantation, the tumours obtained 

 come to represent less and less all the constituent cells of any entire tumour 

 in the preceding transplantations made during the long-continued experimental 

 propagation. In order that they should do so it would be necessary to mix 

 homogeneously all the tumours obtained at each series of implantations. The 

 purposes of our investigation were fulfilled by the method of repeated 

 subdivision and isolation. By this method a repeated analysis of the power 

 of growth of small groups of cells and their descendants can be obtained. 

 The limited number of centres of growth represented in any single graft can 



able size, - 75 to 1'5 grammes weight, are rare before 8 to 10 days. As the object of 

 these experiments was to estimate the power of continued growth as distinct from mere 

 transitory proliferation, some such time limit was necessary. Estimates of the percentage 

 of success and of the frequency of the spontaneous cessation of growth in tumours which 

 had established themselves must exclude transitory proliferation of the cells introduced 

 and inflammatory swellings at the site of inoculation. 



* The weight of the fragments inoculated into each animal has been arrived at by 

 weighing the mass of tumour used for transplantation and dividing by the number of 

 animals used, e.g., 1 gramme of tumour transplanted into 100 mice gives O'Ol gramme per 

 implantation. 



