PROTOZOA AND THE CANCER PROBLEM 207 



cases indefinitely continued protoplasmic existence is bound up with 

 the phenomena of fertilization and inheritance. The cancer cell, so 

 far as we know, undergoes no process analogous to fertilization. 

 Farmer, Moore, and Walker ('03) have described "hetero typical" 

 mitosis in cancer cells, and claim that, as in germ cells, this is evidence 

 of the preparation for fertilization, but numberless critics have shown 

 that it indicates only the degenerative changes which the majority 

 of the cancer cells that are formed must undergo, since all that are 

 formed cannot find nourishment, or escape the protective reactions 

 of the host organism. Cytologists, also, are constantly demonstrating 

 that heterotypical mitosis is a form which the mitotic figure may 

 assume under almost any abnormal condition ; Haecker ('04) obtained 

 them in embryonic cells treated with ether and other poisons, while 

 Bonnevie ('07) has shown that they are common enough in normally 

 developing cells of different animals and plants. The further obser- 

 vations of the English observers as to a reduced number of chromo- 

 somes in cancer cells are more safely explained upon the lines early 

 laid down by Hansemann ('93), as due to abnormalities brought about 

 by deranged mitotic figures in degenerating cells. 



It is beyond the scope of the present volume to discuss the various 

 theories that have been advanced to explain the source of the stimu- 

 lus to cancer-cell proliferation. Ewing ('08), in an excellent summary 

 of the present status of the cancer problems, broadly divides all theories 

 into two categories, which he designates the parasitic theory and the 

 cell-autonomy theory. The former, held by von Leyden, Behla, 

 Borrel, Gaylord, and a host of others, interprets cancer as due to the 

 action of some foreign living organism stimulating the cell to divide, 

 and so to produce the primary tumor, and by its continued presence 

 maintaining the stimulus to proliferation. The other theory, held by 

 the great majority of pathologists and medical men in some form or 

 other, and taking concrete form in the theories of Cohnheim, Ribbert, 

 Ehrlich, Ewing, and others, interprets cancer as due to the breaking 

 loose of some cell or cells from the regulating control of the organism 

 and starting off on an independent career of lawless development. 



Against the former theory must be charged the fact that no specific 

 parasite has been continuously found in human or animal cancer, 

 nor does the clinical history of the disease furnish anything similar to 

 that of known infectious diseases. Against the latter must be raised 

 the important objection that in no form which the theory assumes is 

 there a satisfactory explanation either of the cause of cancer or of the 

 power of continued proliferation. It is true that normal vital processes 

 are not yet sufficiently known to enable us to predict what might 

 happen under abnormal conditions, and with those who are pessimistic 

 enough to believe that the problems of cancer and of life itself are all 

 one, we may assume that only in time will further knowledge show 



