Living Radiators

BY PItOFESSOIt JULIAN HUXLEY.

N 1923, Gurvich, a Russian biologist, announced a peculiar discovery. If you took an onion-root (still attached to the parent onion, Men entendu) and pointed it at the side of another root, it exerted a stimulating effect on the target, so that the cells on the side nearer the first root began to multiply faster than those on the side away from it. The root had to be proPerlY aimed if the influence emanating from it was to hit the target : it acted like a biological pistol.

.These experiments were first of all received with considerable scepticism, which was not diminished by the fact that Gurvich originally saw in them proof of the existence of a " vital force," raying from tissue to tissue. A year later, he abandoned this attitude, having discovered that the discharge of his biological pistols would pass through quartz but not through glass—a fact which immediately suggested that the influence was ultra-violet light. Unfortunately, however, although photographic plates are very sensitive to ultra-violet light, the root-tips quite failed to have any effect upon them ; and so the scepticism continued. Nothing daunted, Gurvich and his pupils continued with their experiments. They found that besides plant-roots, other things, such as muscles or tadpoles' brains, would exert this effect ; other things too, such as cultures of yeast or bacteria, would act as detectors of the effect, multiplying more rapidly when hit by the mysterious rays. Papers poured out from Gurvieh's institute, and after some five years the accumulation was enough to be summarized in a book. The, rays were christened mitogenetic rays, from their power of provoking cell-division, which is technically known as mitosis. But scepticism continued ; other workers failed to obtain the same results, and criticized Gurvieh's methods..

Then the tide began to turn. Independent workers, first in Germany and then in America, confirmed the most important results. They found that- the rays did exist, that they did have this stimulative effect upon cell- division, that they could be reflected and refracted as they ought to be if they were light-rays, that they did belong to the ultra-violet series. But a good deal of mystery still remained. Ultra-violet light produced by ordinary physical means did not always produce the stimulating biological effect ; when it did, the effect was not so strong ; and the biological rays obstinately refused to be recorded on a photographic plate or by any other physical method.

The problem, however, has at last been solved. Various details remain to be worked out, but the main principles seem clear. It was solved by a fruitful eolla hit ation between biology and physics—biology in the person of Gurvich and his collaborators, physics in that of Joffe, the distinguished director of the Institute of Pure and Applied Physics at Leningrad.

The first part of the residuum of mystery, as to why the mitogenetic rays did not affect a photographic plate, was resolved by physical methods. An ingenious in- strument was devised which, by electrical means, could detect infinitesimal quantities of light rays or ultra- violet rays falling upon it. With its aid it was shown that the biological influence emanating from the root-tip or muscle or what not did indeed consist of ultra-violet light, but in quantities far below the power of any photographic plate to- detect. To darken a plate, the biological rays would have to be about a million times stronger than they actually are.

The exact nature of the rays and their position in the spectrum could also be discovered. Their wave-length ranges between 2,000 to 2,300 Angstrom units : ita other words, while the visible spectrum covers a whole octave of light, the mitogenetic rays are restricted to a narrow band, only about a seventh of an octave in extent.

These two discoveries led to the clearing up of the other part of the mystery—why ordinary ultra-violet rays from the sun or an artificial source secured not to have the same effect on living tissues as did the mito- genetic rays. This turned out to be partly an effect of the. quality of the rays, partly of their intensity. The range covered by the mitogenetic rays constitutes only a small portion of the range of ultra-violet rays. But outside this narrow band, radiations of. other wave- lengths may have no effect or may even inhibit cell- division instead of stimulating it. In the second place, the stimulative effect of the rays, even of the right wave-length, is greatest at very low intensities. After that, it begins to decline, is already well below its maximum at the intensity which will just affect a photo- graphic plate, and of still lower efficacy when radiation of any ordinary strength is used.

These latter results were made poisible by a most ingenious combination of physical and biological methods. Instead of using as a biological 'detector apiece of onion Mot which you must first cut into thin slices and then examine under the microscope to count the number of dividing cells on near and far sides, Joffii used a standard culture of bacteria in standard bouillon. If a beam of light is passed through such a culture, a certain amount of it is scattered to right and left by the minute bodies of the bacteria ; and the amount so scattered is directly proportional to the number of bacteria present, and this, of course, depends on hinv much they have been stimulated to grow and divide. Accordingly, as measure of the biological effect of ultra-violet rays, .7offe took the amount of light scattered by the bacteria at right angles to the main beam—of which an accurate and rapid measure can easily be taken.

Another very recent discovery of Gurvich is that cells during a certain period of their growth can take up the minute packets of ultra-violet radiation given off by onion roots and so forth, and can then discharge the same type of radiation again, but in larger quantities, thus acting as relays. In this way the original effect can spread considerably beyond the target actually hit by the rays.

Many tissues have this property of emitting these mitogenetic or weak ultra-violet rays ; but they possess it in very varying degrees. Ordinary muscle has it strongly, but nitwit more is given from muscle which is actively, contracting than from resting muscle. Even different regions of a single beating heart emit different amounts- of the- rays. It seems that the rays are given off only by a thin surface layer of living substance ; no animal with a tough skin emits them, for they are kept in by the skin layer.

• The- rays cams -be used to do sonic very queer things. Those from a fish's heart, if directed against unfertilised sea-urchin's eggs, cause them to take the first step

towards parthenogenetic, " fatherless" development. .Those from bacteria will make dormant niosquitO eggs hatch out prematurely into wigglers, and will cause' highly abnormal development in the little larvae of sea-nrehins.

Many workers have found that single-celled 'Organisms will multiply faster when there are several 'together in a drop of fluid than when they arc kept isolated, even in the most favourable conditions. It is prObable that this has to do with the rays with which they-lsomlird each other ; and the Mule mutual stimulatioif amid co- ' operative acceleration of development probably OCcu IN also in the early stages of the development of thelttfflized egg when it is rapidly dividing into many cells.

Finally Joff6 and his collaborators have shown that just the same sort and intensity of Ultra-violet radiation is given off by many chemical processes taking place in inorganic matter outside the living body. Thus their emission by onion roots or yeast cells or vertebrate muscles is not in any way a specifically vital property, but is due to the fact that chemical processes of the same nature are a necessary part of the chemistry of life—a by-product of • material existence. Once there, such properties can be turned to biological account, as has happened with the electrical organs of fish, which turn to specific biological use the universal property of matter to show slight electrical changes when it changes chemic- ally. And though Gurvich's mitogenetic rays are prob.- ably in many cases quite useless to the organiSin by which they are being emitted, it is 'probable- that in other cases they are being employed to accelerate

ccll- division where needed, and to co-ordinate develcitinient.

Here is at least a new field of biological'kiMieledge. In the past decade the subject has passed from improbable mystery to accurate scientific respectability ; it • now remains to push forward and discover just what use organisms have made -of this hitherto unsuspected property of their natures.