th, hard-wood body without finger-holes,
weighted in the centre with lead disks and capped with polished brass
disks, with a steel ring on the outside. Its weight must be 4-1/2 lb.,
its outside diameter 8 in. and its thickness at the centre 2 in. It must
be thrown from a 7-ft. circle, which may not be overstepped in throwing,
and the throw is measured from the spot where the discus first strikes
the ground to the point in the circumference of the circle on a line
between the centre and the point of striking.

DISINFECTANTS, substances employed to neutralize the action of
pathogenic organisms, and prevent the spread of contagious or infectious
disease. The efficiency of any disinfectant is due to its power of
destroying, or of rendering inert, specific poisons or disease germs.
Therefore antiseptic substances generally are to this extent
disinfectants. So also the deodorizers, which act by oxidizing or
otherwise changing the chemical constitution of volatile substances
disseminated in the air, or which prevent noxious exhalations from
organic substances, are in virtue of these properties effective
disinfectants in certain diseases. A knowledge of the value of
disinfectants, and the use of some of the most valuable agents, can be
traced to very remote times; and much of the Levitical law of cleansing,
as well as the origin of numerous heathen ceremonial practices, are
clearly based on a perception of the value of disinfection. The means of
disinfection, and the substances employed, are very numerous, as are the
classes and conditions of disease and contagion they are designed to
meet. Nature, in the oxidizing influence of freely circulating
atmospheric air, in the purifying effect of water, and in the powerful
deodorizing properties of common earth, has provided the most potent
ever-present and acting disinfecting media. Of the artificial
disinfectants employed or available three classes may be
recognized:--1st, volatile or vaporizable substances, which attack
impurities in the air; 2nd, chemical agents, for acting on the diseased
body or on the infectious discharges therefrom; and 3rd, the physical
agencies of heat and cold. In some of these cases the destruction of the
contagium is effected by the formation of new chemical compounds, by
oxidation, deoxidation or other reaction, and in others the conditions
favourable to life are removed or life is destroyed by high temperature.
Among the first class, aerial or gas