This is a piece of knowledge of the utmost importance to mankind, for we know that malarial disease in tropical countries—which, after all, in the future will be the most important parts of the world, seeing that they can produce more food than temperate countries and can therefore support a larger population—causes more deaths and more disposition to death by inducing cachectic states predisposing to other affections than all the other parasites affecting mankind put together. We know now in what way this parasite is acquired. Depend upon it, in time, in virtue of this knowledge, we will get enormous power over the disease and sooner or later we will be able to prevent the infection of man by the parasite. It is only a question of study and the application of the knowledge already acquired, only a question of money and perseverance and a little ingenuity, and these results will come. It may not be in ten years or twenty years, but sooner or later the energies of a considerable portion of scientific mankind now being expended in endeavoring to devise means for preventing the infection of men with the malarial germ by the mosquito will bear valuable fruit.
You can readily understand that it is of great importance to be able to recognize the special species of mosquito which convey malaria. The effective species as regards human malaria belong to the genus anopheles; species of the genus culex are effective in the case of sparrow malaria. Fortunately, these two genera are easily recognized even by the amateur zoölogist. If you find a mosquito clinging to the wall or other surface you can tell which genus it belongs to by its posture. If the body is stuck out nearly at right angles to the surface on which the insect is resting, it is an anopheles. If the body is almost parallel to the surface, it is a culex. There is another test which is easily applied if you have a pocket lens; in culex the two organs known as palpi are rudimentary and very short; whereas in anopheles those organs are almost as long as the proboscis. It should be remembered that the male mosquito is not a blood-sucker and therefore is not dangerous. It is the female anopheles which transmits the disease. The mosquito larvæ inhabit stagnant or slow-running water. If a mosquito larva be found with its head downwards, the body hanging at right angles to the surface of the water, it is a culex; if the body lies parallel to the surface of the water, it is an anopheles. There are other points of difference with which I need not now trouble you; those referred to suffice for diagnosis between the innocuous and the dangerous mosquitoes.
The facts regarding the malaria parasite which I have described are of great importance for many reasons. First, because they help us to understand the pathology and etiology of malaria. Secondly, they help us in diagnosis. Thirdly, our knowledge of the parasite is invaluable in directing treatment. Lastly, a knowledge of the life-history of the malarial parasite is of extreme value for the prevention of malarial disease, for could we by mechanical or other arrangements prevent the mosquito attacking the human body, we could prevent the malarial parasites from entering the human body; or if we could abolish the mosquito by drainage or other means from a country, then we might be sure that we would abolish the malaria of that country also.
Attempts are being made to solve these practical problems. At the present moment such attempts are being actively made in Rome by Professor Celli and elsewhere by others. I have no doubt that in the course of a few years we shall get some very valuable results in this direction and that, thanks to this new-born knowledge about the malarial parasites, better times are rapidly approaching for malarial countries.
NEW SOURCES OF LIGHT AND OF RÖNTGEN RAYS.
By HENRY CARRINGTON BOLTON, Ph. D.
Among the general laws of physical science, none seems more firmly established than that of the conservation and correlation of energy; according to this the various forms of energy that constitute the domain of experimental physics, heat, light, electricity, magnetism and chemical action, have reciprocal dependence and “can not originate otherwise than by devolution from some preëxisting force,” or rather energy. That motion is convertible into heat, heat into light and both the former into electricity are phenomena familiar to every one who uses incandescent bulbs or rides in a trolley, and we do not usually recognize any production of light unaccompanied by heat. True, the little fire-fly is possessed of a mysterious power that enables it to emit light without enough heat to affect Langley’s most sensitive bolometer, but the eminent Secretary of the Smithsonian has to admit that the “cheapest form of light” is produced by “processes of nature of which we know nothing.” This little understood property called phosphorescence is shared by many living organisms, both animal and vegetable, as well as by substances of the mineral kingdom; to the former belong coelenterates, mollusks, crustacea, fishes and insects, and decaying wood, certain mushrooms, etc.; to the latter the Bologna stone, so-called, and the commercial article called ‘Balmain’s paint.’
In the case of the mineral substances, barium or calcium sulfids and the like, the light-giving power is not an innate property, but is set in operation by exposure to the energy of sunlight, the light of burning magnesium or to some other source of actinism; moreover, the power thus acquired by insolation is a fugitive one, the substances exercising it after three or four hours become ‘dead’ and lose their activity. Excepting then these living beings and these phosphorescent bodies, light as commonly known to us is always correlated with heat; within the last four years, however, discoveries have been made in France that seem to modify the position taken by philosophers and to necessitate new views concerning the manifestations of that energy with which the universe is endowed. A group of French savants have found mineral substances that apparently give out light perpetually without any exciting cause, realizing the dream of the alchemists—a perpetual lamp consuming no oil. These substances also emit rays having the penetrating properties of X-rays, other rays affecting a photographic plate, and fourthly, rays causing air to become a conductor of electricity. The history of these discoveries can be briefly given.
Röntgen’s discovery of the rays that pass through metals and solids opaque to light was made in 1895, and in the following year, Becquerel, a distinguished French academician, discovered that salts of the metal uranium (substances that had long been used in coloring china and glass) emit invisible radiations capable of discharging electrified bodies and of producing skiagraphic images on sensitive plates; he found that potassio-uranic sulfate emits rays that pass through black paper and give photographic impressions in the same way as Röntgen rays. This property is not limited to the brilliantly fluorescent uranic salts, but is shared by the non-fluorescent uranous salts, and is exhibited by compounds whether phosphorescent or not, whether crystalline, melted or in solution, as well as by the metal itself. The permanence of this activity is amazing, substances kept in a double leaden box more than three years continuing to exert the power.