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.