PROTOZOA AND THE CANCER PROBLEM 209 



vitality is renewed by parthenogenesis, and they fail for the most part 

 to see that their supposed applications of this biological phenomenon 

 are far more improbable than the parasitic theory which they deride. 



^lany advocates of the theory of cell autonomy go so far into the 

 other camp as to believe that the cancer cell is itself a parasite. This 

 parasitism is shown by the fact that when placed in a suitable medium 

 it reproduces cells similar to itself and continues to multiply in this 

 way, without showing signs of differentiation into organs, a phenom- 

 enon which has given rise to the term " infectivity" of cancer cells, and 

 it certainly is an attribute which parasites possess. Bashford, Murray, 

 and Bowen ('06), confirmed later by Hertwig and Poll ('07), made the 

 observation, based upon statistical data, that the growth energy in 

 these cancer cells in mice undergoes rhythmical variations in vigor and 

 depression. Calkins ('08) found similar rhythms, based upon the 

 records of the New York State Cancer Laboratory, but showed that 

 the rhythmical variations were not in the growth energy of the cancer 

 cells, but in the infectivity of these cells, the growth energy and infec- 

 tivity showing no relationship after the tumor is established in trans- 

 plantation. 



The advocates of the parasite theory believe that the cancer cell 

 became a parasite in the above sense, not from any derangement of 

 metabolic processes, nor from any vague, hypothetical, inherent 

 tendency to cellular anarchy, but because of the susceptibility to the 

 poisonous stimulus of some parasite. In this they are supported by 

 the facts of gall formation in plants, where a known poison, secreted 

 by insects, stimulates the latent division energy of the plant cells, and 

 a tumor is produced. The counter argument, so often made, that such 

 abnormal growths are nothing like cancer, is certainly true; the 

 analogy, however, is not with the form which the growth assumes, but 

 with the cell which is stimulated to divide by the activity of a parasite. 

 Among other things, the gall differs from the cancer cell in having 

 no infectivity, the stimulus not being continuous. 



Another analogy is drawn from the great tumor-like growths in 

 certain vegetables (crucifera*), due to the presence in the root cells 

 of a protozoon parasite, Plasmodiophora hrassicae. These growths, 

 known as club root, hanburies, fingers and toes, etc., are highly 

 infectious and are frequently a serious menace to market gardens. 

 The organism causing the tumors penetrates the root hairs of the 

 caiii)age or other allied vegetal)les, in the form of a minute ameboid 

 flagellate (Woroiiin, 1S7S, Prowazck, V30'). Two or more may 

 enter the same cell, where, immersed in the fluid cytoplasm, they lose 

 their flagella and grow into larger ameboid organisms (Fig. 62, j). 148). 

 Later, these ameboid cells fuse, forming, as in all myxomycetes, a 

 syncytium or plasmodium. The infected cells are caused to divide 

 by the presence of the parasite, the infcctivl cells thus carrying the 

 14 



