WATER.

129

Hydros-

ence of a galvanic battery, it is decomposed into two gases—namely, one volume of oxygen, and two volumes of hydrogen. These

gases, in the proportions just men-tioned, may be made to recombine, andform water, by heat, electricity, or spongyplatinum.

leq.Steam=9

Eq. or At. Eq. Wt. Per Cent. Berz.&Dulong. Vol. Sp. Gr,

Hydrogen .

. 1 .

. 1 .

. . 11-11 . .

. . 11-1

Hydrogen gas . .

,i ...

. . 0-0694

Oxygen . .

. 1 .

. 8 .

. . 88'88 . .

. . 88-9

Oxygen gas . . .

. 0-5 . .

. . 0-6555

Water . . .

. 1 .

.. 9 .

. ioo-o’o . .

. 100-0

Aqueous vapour .

. 1 . . .

. . 0-6249

Physiological effects. —Water is a vital stimidus ; that is, it is oneof the external conditions essential for the manifestation of life. It con-stitutes four-fifths of the weight of the tissues, and is the source of theirphysical properties, extensibility and flexibility. Considered in a diete-tical point of view, it serves at least three important purposes in theanimal economy : namely, it repairs the loss of the aqueous part of theblood, caused by the action of the secreting and exhaling organs;secondly, it is a solvent of various alimentary substances, and, therefore,assists the stomach in the act of digestion, though, if taken in very largequantities, it may have an opposite effect, by diluting the gastric juice ;thirdly, it is probably a nutritive agent, that is, it assists in the formationof the solid parts of the body.

In a medicinal point of view, the physiological effects of water aremuch modified by its temperature.

(a.) Effects of tepid water .—Water moderately warm, and whichneither cools nor heats the body, acts locally as an emollient, softeningand relaxing the various tissues to which it is applied. When swallowedit allays thirst, becomes absorbed, mixes with, and thereby attenuates, theblood, and promotes exhalation and secretion, especially of the wateryfluids. Administered in large quantities it excites vomiting. The con-tinued excessive use of water has an enfeebling effect on the system, bothby the relaxing influence on the alimentary canal and by the excessivesecretion which it gives rise to.

Injected into the veins in moderate quantities, tepid water has noinjurious effects ; it quickens the pulse and respiration, and increasessecretion and exhalation. Large quantities cause difficulty of breathingand an apoplectic condition. Thrown with force into the carotid arteryit kills by its mechanical effect on the brain. I have already (p. 23)made some observations on the action of water on the sanguineousglobules out of the body.

(, b .) Effects of ice, snow, and ice-cold water. —The temperature of theseagents is not higher than 32° F. When brought in contact with a livingpart, they produce two series of effects—the first of which may be deno-minated direct, primary, or immediate; while the second may be termedindirect, secondary, or mediate, since they are developed by the vitalactions, after the cold agent has ceased to act.

a. Of the primary effects. —When ice is applied to the body, itabstracts heat, causes pain, reduces the volume of the part, and diminishes

K