no SCIENCE PROGRESS 



mice and since then the number of successful transplantations 

 has been enormous. The obvious advantages of using so 

 small and cheap an animal adequately account for its popularity 

 for experimental purposes. Whether malignant growths are 

 really more common among mice than other mammals, as has 

 been suggested, is very doubtful. In the case of no other 

 animal have hundreds of thousands, perhaps millions, been 

 kept for the particular purpose of making observations upon 

 cancer and for breeding experiments. All that has been 

 suggested by the facts is that cancer is nearly as common as 

 it is in human beings and that, therefore, it may also be common 

 in other mammals, though we have no data at present upon 

 which to base a definite statement. 



Some important points with regard to cancer have been 

 established by these experiments. Cancer is transmissible 

 from individual to individual but only through the transference 

 of the living cells of the growth from the individual in which 

 they originate to a suitable position in the body of another 

 individual. The cells of the growth, though they may live and 

 multiply for some time in a closely related animal, 1 are only to 

 be established in an animal of the same variety of the same 

 species and the more nearly the animals are related to each 

 other, that is to say, the nearer their common ancestry, the 

 greater will be the percentage of successful graftings. 2 It is 

 certain that these transplantation tumours grow from the trans- 

 planted cells and not from the cells of the new host. 3 



Successive generations of tumour, that is to say, successive 

 sojourns in fresh individuals as hosts, if the hosts are of the 

 same near ancestry, increases the percentage of successful graft- 

 ing. The rapid passage through successive hosts increases the 

 rapidity of the growth of the tumour. 4 



With regard to the experiments demonstrating this latter 



1 Ehrlich, Arb. a. d. k. Inst. f. exp. Therap. zn Frankfurt a/M., Jena, 1905, i. 

 77; Apolant, Therap. der Gegenwart. Berlin u. Wieti, 1906, xlvii. 145; and 

 many others subsequently. 



2 Jensen, Central./. Bakteriol. u. Parasit, Jena, 1903, xxxiv. 122; Haaland, 

 Berl. klin. Wohnschr. 1907, xliv. 713 ; and many others. 



3 Jensen, op. cil. ; Loeb, Journ. Med. Research, Boston, 1901, vi. 28 ; and 

 very many others. 



4 Ehrlich and Apolant, " Beobachtungen uber maligne Mausetumoren," Berl. 

 klin. Woch. 25, 1905, and ibid. " Experimented Beitrage zur Geschwulstlehre," 6 

 1906. 



