WORLD OF SCIENCE

Te Awamutu Courier, Volume 60, Issue 4235, 24 January 1940, Page 4

WORLD OF SCIENCE

VIRUSES AND CANCER.

(By Dr

E. Weston Hurst.)

When cells of the body die or are destroyed by injury, other cells multiply to take their place. Not infrequently cells multiply without apparent reason, forming a tumor or neoplasm. If the increase of cells is relatively moderate and is confined locally, a benign tumor results; if proliferation is unlimited and bits of tumor are dislodged and carried to distant parts of the body, a malignant neoplasm, known popularly as cancer, is the outcome.

In animals it is often possible to transfer a malignant' neoplasm to a fresh host of the same species by grafting a fragment of the tumor into a suitable part of the body. From time to time various parasitic theories of the causation of cancer have arisen, attributing the growth to the action of protozoa, bacteria, and so on, but none has withstood careful investigation. The modern variant of the parasitic theory, postulating the action of a filterable virus, is based on sounder reasoning, and, although only five years old, seems more likely to Apart from their intense interest to the biologist, the observations on which it is based must convince the layman that definite progress has been made in understanding this much-feared malady, which has presented so difficult a problem of medical research. In domestic fowls a number of malignant tumors occur, and many of these have been traced to the action of filterable viruses. Although these tumors are not infectious in the popular sense of the term, the viruses from them when injected into other fowls produce fresh tumors, and by this means they can be propagated indefinitely; in such experiments no actual tumor cells are introduced into, the new host.

From 1910, when the first of these tumors was discovered, until 1934, the scientific world was divided as to the significance of these observations. A few doubted that the condition set up by the virus was really a tumor,

a few that the tumor-producing agent was really a virus. Many, agreeing that the condition was a tumor and the causative agent a virus, maintained that it was impossible to apply this knowledge to the problems of human disease, especially as no animal or human tumor had been shown to be caused by a virus. The last objection has now “been removed. Most viruses cause necrosis or death of the cells of the body susceptible to their action, hence the blisters or pocks constituting the rash of smallpox or chicken-pox and the loss of muscular power in infantile paralysis. If, however, the lesions of many virus diseases are studied carefully with the microscope in their earliest stages, it is seen that before the affected cells die they are induced to multiply considerably. Such increase is only transient, and at first sight bears no resemblance to the unlimited multiplication of cells in cancer.

In 1932 there was isolated from a certain “tumor” occurring in wild American rabbits a virus which produced within a few days a large tumor-like mass in the fibrous tissues; the increase of cells was not maintained, however, and invariably the “tumor” gradually disappeared. Microscopically, the affected cells multiplied in a manner much more like that in neoplasms than in ordinary virus diseases, but the process was not wholly similar to that in the fibromata (benign neoplasms of fibrous tissue) in man. In 1933, again from wild American rabbits, another virus whs isolated; this caused great proliferation of the epidermal cells of the skin, exactly as in human and animal warts (or papillomata) which are frequently benign neoplasms of a variety of species. Unlike the “fibromata” mentioned above, the warts grew over a period of many months and showed no tendency to disappear. From them, however old they might be, the virus could be isolated and made to infect fresh animals with the production of more tumors. The warts could be reproduced in a fresh host either by using preparations free from tumor cells, showing the presence of a virus, or by grafting pieces of tumor by the method commonly used for mammalian tumors in which no /virus can be detected. For convenience in the laboratory, the American scientists now infected ordinary domestic rabbits by cell-free preparations failed, though actual fragments of tumor tissue grew readily in fresh animals; that is to say that is to say that in the warts or cancers of domestic rabbits no direct evidence of the presence of a virus could be obtained, a state of affairs on all fours with that in mammelian cancers in general. But if the blood of rabbits to which the warts had been thus transplanted were examined, antibodies to the virus were readily detected, showing that the virus was actually present in the fragments though not demonstrable by the usual methods. Thirdly, if a fragment of wart were transplanted from the skin to a site such as the muscles where it had a better blood supply, it often became cancerous at once. Fourthly, if the skin of a rabbit were irritated for several weeks by applications of tar, and then injected into the blood stream, the irritated areas immediately developed cancer. Other evidence of a more complicated nature suggested that the virus responsible for the malignant tumors of fowls consists of two components firmly welded together, one the virus proper which may be common to a number of tumours, the other a constituent of the cells stimulated to malignant growth. The latter is the factor responsible for the choice of cells which are induced to multiply without restraint.

The strength of the modern theory of the causation of cancer lies in the fact that it takes into account the important predisposing effect of injury, long-continued chemical or mechanical irritation, etc., factors which have long been known to be connected with the development of malignant tumors. The actual excitant of cancer is believed to be a virus. We believe that one or more (but only a small number of) cancer viruses exist, and may infect a given kind of cell either spontaneously or more usually as the result of mechanical or chemical irritation. The virus enters into very intimate union with some exceptional cases such as that of the warts of wild American rabbits or the malignant tumors in fowls, the virus is no longer demonstrable. The affected cells are caused to multiply indefinitely, and since the cellular component of the virus-cell complex determines that only a particular kind of cell shall undergo this change in behaviour, cancer appears as a disease in which one cellular element of the body multiplies out of all proportion to the needs of the organism.