Such, then, has been the history of the bubonic plague. No other epidemic disease can be traced authentically as far back as the ‘Black Death.’ The characteristic symptoms, the rapid death, the excessive mortality are all features which have been noted through more than twenty centuries. The plague bacillus discovered in 1894 by Yersin, judged by its effect, is neither more nor less virulent than its early progenitors. It has often died out in a given locality or country, it has even been forced back to its original ancestral home, but still the same type, the same species has perpetuated itself unchanged. If the plague on its present world-wide journey does not cause such terrible outbreaks as it has in the past, it will be not because the germ has been altered by time, but because man has changed in so far as he has slowly learned and profited by the lessons of previous epidemics. GASOLINE AUTOMOBILES. BY WILLIAM BAXTER, JR. To understand the operation of a gasoline vehicle it is necessary to be somewhat familiar with the principle on which gasoline motors act. Briefly stated, it is as follows: The gasoline is converted into a vapor, and in this state is mixed with a sufficient amount of air to cause it to ignite when heated to a proper temperature. This mixture of air and vapor is admitted into a cylinder in which a piston moves freely, this part being substantially the same as in a steam engine. By means of an electric spark or a hot tube, the mixture is ignited, burning so violently as to expand the products of the combustion with such rapidity as virtually to become an explosion. The force of this explosion pushes the piston to the further end of the cylinder, and by means of a connecting rod and a crank this movement imparts a rotary motion to a shaft. [Illustration: FIG. 1. GASOLINE MOTOR.]