Persons may sometimes withdraw the piston or plunger from the barrel, and on account of its peculiar construction be unable to return it again. Therefore, please observe that it is composed of two round pieces of leather, which are turned in opposite directions over the metallic plates--_the upper one turning up, the lower one turning down_. With the leathers thus arranged, it is to be introduced sideways into the barrel, and the portion of the lower leather which remains outside of the barrel gradually and carefully pressed in with the thumb nail. ☞ But in so doing be very careful not to cut or injure the leather. N. B.--Silver Plated Syringes, suitable for using nitrate of silver, furnished to order at short notice. (See _Nitrate of Silver Injections_.) Peculiarities of the Improved Portable Syringe. The peculiarity of this instrument, which renders it superior to others heretofore used, consists in the mode of constructing the valves and valve chambers. Many of the celebrated instruments with which the market has been heretofore supplied have been constructed with cylindrical valve chambers, having a flat seat for the valve to rest upon, through which is an orifice for the passage of the fluid. The valve itself consists of a circular piece of India-rubber, the diameter of which is somewhat less than that of the chamber, in order to allow the fluid to flow by it when the valve is raised. There are several serious objections to these valves. The India-rubber in a short time enlarges when in use so as entirely to obstruct the passage of the fluid, especially when a warm injection is used, which quickly softens and moistens the rubber. The valve, too, in such cases, if made so small and light as to avoid this evil, is liable to double or fold up, and is drawn through the orifice in the valve neck into the barrel of the instrument, and thereby entirely stops its working. In the instrument now offered to the public, these objections are entirely obviated by using for a valve a small mineral ball, which rests upon a concave seat, to which it is nicely adjusted. The ball, being of a material which does not absorb water, never becomes enlarged by use; and it is obvious that it can never be drawn through the orifice into the body of the instrument. It is also a self-adjusting valve, the friction of the ball on its seat having a constant tendency to make them fit together more accurately. The mineral balls are acknowledged to be much more durable than the India-rubber disks; and as an instrument is serviceable only while all its parts are fit for use, it is apparent that the new instrument will last much longer than those which have been constructed in the manner described. Care and Preservation of the Instrument.