39^ Tumors. 



that some otlier as yet unknown causes underlie the irregular pro- 

 gressive proliferation which these cells manifest (in other words, 

 that the epithelial multiplication is the primary process) ; and search 

 lor some kind of infectious agent is not as yet abandoned. The 

 occasional endemic occurrence of cancer (also observed bv Eggel- 

 ing in hogs in a certain locality) and isolated cases which suggest 

 the transmissibility of certain forms of cancer continue to keep the 

 question of the infectiousness of cancer in discussion. A. Sticker, 

 for example, has called attention to a dog which for a long time 

 liad been in the habit of lying by the bed of a man suffering from 

 cancer of the stomach and ate all sorts of material which the man 

 had vomited, and which became affected by a general carcinomato- 

 sis (lungs, liver, omental sac. but not the alimentary canal). This 

 may have been a mere coincidence, but the possibility of an etio- 

 logical relationship between the two cases cannot be entirelv ig- 

 nored. ( Cf. p. 334. ) Experimental attempts to prove an infectious 

 nature as existing in these growths (inoculation and feeding ex- 

 periments) have hitherto always failed. Trasbot obtained no posi- 

 tive result from hundreds of such attempts : Duplay and Cazin 

 failed in over one hundred and twenty experiments in dogs and rats ; 

 Gratia and Lienaux, Cadiot and Gilbert had no more success in 

 numerous attempts to transmit tliese tumors, employing all sorts 

 of methods of inoculation (from dog to dog, from man to dog). 

 The transplantation of certain forms of cancer in rats and mice has 

 alone succeeded (Hanau. ]\Ioraus. C. O. Jensen) : but the methods 

 employed do not indicate that an infectious agent was operative^ 

 but rather that the cells of the cancer used in the experiment were 

 capable of multiplying if placed in uninjured condition in a new 

 specifically similar soil (i. e., transplanted to the same species of 

 animal as that from which derived), and of continuous develop- 

 ment into an independently growing tumor tissue in their practically 

 parasitic colonization and multiplication, (cf. Definition of tumors 

 P- 325-) [Transplantation of cancers in animals has invariably 

 shown that success is to be expected only when the animal to which 

 the tumor is transplanted is of the same species as that from which 

 it was derived, even varieties of the same species making the result 

 doubtful. In this country Leo Loeb, Gaylord, Herzog and others 

 have carried various cancerous growths or mixed cancers through a 

 number of generations in rats and mice. In these experiments actual 

 portions of the living growth (bits may retain life for some hours 

 -when kept in moderate refrigeration after removal from the origi- 

 nal animal) must be introduced into the experiment animals and 



