208 PARASITISM 



how the power of regulation may be lost to these specialized tissue 

 cells, and the power of endless proliferation gained. To say, as 

 Adami ('01) does, that in cancer cells the "habit of growth" has 

 replaced the "habit of work," or to admit with Oertel ('07) that if 

 a gland cell can be induced to excessive secretion we might with equal 

 right expect it to be induced to divide excessively, is simply to say 

 with Hertwig ('04) that the cells of carcinoma have changed from an 

 "organotype" into a "cytotype." Such statements, forming the real 

 substance of many polemical writings on cancer, merely state the 

 problem and are perfectly true, for cancer, or malignant growth of 

 cells, does exist. These truths do not furnish any clue to the cause 

 which underlies the abnormal growth, nor do they in any way explain 

 the apparent power of endless growth which the cancer cell, unlike 

 any other mammalian cell, possesses. The phenomena of normal 

 regeneration cannot be invoked ; a begonia plant or hydra animal may 

 be cut into small pieces and each will grow into a perfect organism, but 

 here in these generalized forms, apparently, the all-important germ 

 plasm is present in all cells, and they are widely different from the 

 highly specialized, physiologically unbalanced, tissue cells of mammals, 

 and are always subject to the coordination and regulation of the organ- 

 ism, as a whole. 



On the other hand, the parasitic theory of cancer in its naked form 

 is altogether too simple an explanation, and the clinical symptoms of 

 the disease diflfer so widely from those of different germ diseases, as to 

 weigh heavily against it. Nevertheless, there is some positive evi- 

 dence, as shown by the frequently localized distribution of cancer, by 

 cancer a deux, by the facts of cancer immunity (Gaylord, Clowes, and 

 Baeslack, Ehrlich, "athreptic" immunity), by cage infection (Gaylord, 

 Borrel, Lignieres, etc.), and by the " infectivity" of cancer cells, as 

 contrasted with cells of benign or embryonic tumors, of vegetable 

 galls, or with normal transplanted tissue cells. 



While there is little doubt that the morbid symptoms of cancer are 

 due to the autonomous activity of these malignant growths, the problem 

 is deeper than mere descriptions of the symptoms caused by the onrush 

 of the anarchistic cells, and is resolved into the biological inquiry as to 

 what was the initial cause of the loss of organic regulation and what 

 underlies the secret of their inexhaustible division energy. The advo- 

 cates of the cell-autonomy theory have no satisfactory explanation for 

 the first, but throw the burden of proof upon the biologist and look for 

 enlightenment to the school of experimental embryology and zoology. 

 Nor are their explanations of the continued power of proliferation 

 more successful, for they call upon the mysteries of fertilization, find- 

 ing, with Klebs ('89), Farmer, Moore, and Walker ('03), that epi- 

 thelial cells conjugate with leukocytes, or with Recklinghausen ('96), 

 that they are "fertilized" by fibroblasts, or with Waldeyer ('87), that 



