In the extraordinary capacity for growth possessed by tumor cells, they resemble vegetable rather than animal cells.

There is no limit to the growth of a tumor save by the death of the individual who bears it, thus cutting off the supply of nutrition.

The cells of tumors peculiar to man show a narrow range of adaptation.

They will grow only in the body of the individual to whom the tumor belongs, and die when grafted on another individual.

In the case of tumors which arise in animals, pieces of the tumor when grafted on another animal of the same species will grow, and in this way the growth capacity of the tumor cells has been estimated.