362 V. THE NATURE OF EVOLUTION 



The structure of a cancer cell or of a cell present at a pre- 

 cancerous stage is sometimes transmitted by virus-like protoplasm 

 particles which are often called cancer viruses. The change of a 

 somatic cell to a cancer must be associated with a change of the gene, 

 and accordingly, if a change of a gene is to be called mutation, it 

 may be said that cancer is raised by a mutation. 



The primitive nature of cancer cell has been well established. 

 For example, glycolysis peculiar to embryonic tissues is remai"kable in 

 cancer cells. The capacity of embryonic tissues to incorporate amino 

 acids is much stronger than that of the ordinary ones, and being 

 similar to that of cancer cells (35) (36). Again, it has been shown 

 that in the conversion of normal hepatic cells to cancer there is 

 almost total loss of certain highly specialized functions, including 

 synthesis of fermentable carbohydrate from pyruvic acid and forma- 

 tion of acetoacetic acid from caprylic acid (37). The pattern of en- 

 zymes of foetal rat liver is said to be more closely related to that of 

 malignant rat hepatoma than that of normal rat liver (38). As al- 

 ready pointed out, primitive structure is so unstable that it may easily 

 be affected by viurses as evidenced by the fact that chick embryos 

 are commonly used as the most suitable tissues for virus cultivation. 

 It is note-worthy that cancer cells also allow viruses, such as those of 

 poliomyelitis (39), St. Louis encephalitis (40), and influenza (41), to pro- 

 pagate in them. 



Greenstein (42) has stressed the fact that all cancerous tissues 

 show a strong resemblance to one another in their chemical pattern, 

 and that the more autonomous they are, the more do they deviate 

 from the chemical pattern of their tissues of origin, and the closer do 

 they approach an apparently functionally undifferentiated type of 

 tissue. 



A series of hormones appear to be required in succession for the 

 development of a germ cell to an adult organism as already mentioned. 

 This must also be the case with the production of cancer cells as well 

 as of germ cells, as the production of these cells is only the reversible 

 reaction of the former, the ontogeny. Sexual hormones may be re- 

 quired at the finishing stage for the completion of the change. Sub- 

 stances commonly termed carcinogenic may be regarded as a type of 

 hormones or hormone-like substances to initiate the change. Many 

 carcinogenic substances are known to exhibit an inducing action like 

 that of the organizer (43), suggesting that they are related to the 

 primitive hormones produced by the organizer. 



Rous and Kidd (44) stated that when carcinogenics are applied to 

 the skin of man, the rabbit, or the mouse, they nearly always elicit 

 benign growth some while before cancer appears, and the latter 



