The great fundamental difference between cancer and any infection lies in the fact that, in an infection, the inflammations and poisonings and local swellings are due solely and invariably to the presence and multiplication of the invading germs, which may be recovered in millions from every organ and region affected, while swellings or new masses produced are merely the outpouring of the body-cells in an attempt to attack and overwhelm these invaders. In cancer, on the contrary, the destroying organism is a group of perverted body-cells. The invasion of other parts of the body is carried out by transference of their bastard and abortive offspring. Most significant of all, the new growths and swellings that are formed in other parts of the body are composed, not of the outpourings of the local tissues, but of _the descendants of these pirate cells_. This is one of the most singular and incredible things about the cancer process: that a cancer starting, say, in the pancreas, and spreading to the brain, will there pile up a mass--not of brain-cells, or even of connective tissue-cells--but of gland-cells, resembling crudely the organ in which it was born. So far will this resemblance go that a secondary cancer of the pancreas found in the lung will yield on analysis large amounts of trypsin, the digestive ferment of the pancreas. Similarly a cancer of the rectum, invading the liver, will there pile up in the midst of the liver-tissue abortive attempts at building up glands of intestinal mucous membrane. This fundamental and vital difference between the two processes is further illustrated by this fact: While an ordinary infection may be transferred from one individual to another, not merely of the same species, but of half a dozen different species, with perfect certainty, and for any number of successive generations, no case of cancer has ever yet been known to be transferred from one human being to another. In other words, the cancer-cell appears utterly unable to live in any other body except the one in which it originated.