Artificial India Rubber.--A recent issue of the Kew Gardens Bulletin contains an interesting article on Dr. Tilden's artificial production of India rubber. India rubber, or caoutchouc, is chemically a hydrocarbon, but its molecular constitution is unknown. When decomposed by heat it is broken up into simpler hydrocarbons, among which is a substance called isoprene, a volatile liquid boiling at about 36° C. Its molecular formula is C_{5}H_{8}. Dr. Tilden obtained this same substance (isoprene) from oil of turpentine and other terpenes by the action of moderate heat, and then by treating the isoprene with strong acids succeeded, by means of a very slow reaction, in converting a small portion of it into a tough elastic solid, which seems to be identical in properties with true India rubber. This artificial rubber, like the natural, seems to consist of two substances, one of which is more soluble in benzene and carbon bisulphide than the other. It unites with sulphur in the same way as ordinary rubber, forming a tough, elastic compound. In a recent letter Professor Tilden says: "As you may imagine, I have tried everything I can think of as likely to promote this change, but without success. The polymerization proceeds _very_ slowly, occupying, according to my experience, several years, and all attempts to hurry it result in the production not of rubber, but of 'colophene,' a thick, sticky oil quite useless for all purposes to which rubber is applied." Dangers of High Altitudes for Elderly People.--"The public, and sometimes the inexperienced physician--inexperienced not in general therapeutics but in the physiological effects of altitude on a weak heart," says Dr. Findlater Zangger in the Lancet, "make light of a danger they can not understand. But if an altitude of from four thousand to five thousand feet above the sea level puts a certain amount of strain on a normal heart and by a rise of the blood-pressure indirectly also on the small peripheral arteries, must not this action be multiplied in the case of a heart suffering from even an early stage of myocarditis or in the case of arteries with thickened or even calcified walls? It is especially the rapidity of the change from one altitude to another, with differences of from three thousand to four thousand feet, which must be considered. There is a call made on the contractibility of the small arteries on the one hand, and on the amount of muscular force of the heart on the other hand, and if the structures in question can not respond to this call, rupture of an artery or dilatation of the heart may ensue. In the case of a normal condition of the circulatory organs little harm is done beyond some transient discomfort, such as dizziness, buzzing in the ears, palpitation, general _malaise_, and this often only in the case of people totally unaccustomed to high altitudes. For such it is desirable to take the high altitude by degrees in two or three stages,