

USES OF WATER. 21 



And in those creatures which at one period of the year are in full activity, 

 but at another lie dormant or hibernate, as they begin to respire more 

 slowly their temperature begins to decline, and when they have sunk into 

 their winter's sleep their breathing is scarcely perceptible, and their 

 warmth scarcely above that of the surrounding air. 



In what has been thus far said we have been considering those oper- 

 ations of the system which tend to the production of heat, causes of cooi- 

 and the maintenance of the whole mass of the body at a tern- ing of the body. 

 perature above that of the surrounding air. But it is obvious that pro- 

 vision must be made to prevent any undue rise, so that between those 

 causes of elevation and these of depression a due equilibrium may be main- 

 tained. If a very large quantity of combustible matter, under the form of 

 food, and about an equal weight of oxygen, are necessary for obtaining a 

 proper heat, we should also recollect that nearly three quarters of a ton of 

 water are consumed each year. The duty which this water 



J J Uses of water. 



discharges we may next consider. 



That duty is twofold. 1st. The removal of solid material in a state 

 of solution ; and, 2d. The production of cold by evaporation. It is the 

 cooling agency which is of most interest to us in our present inquiry, but 

 a few remarks as regards the removal of solid matter may not here be 

 misplaced. 



1st. Water, then, exerts its solvent power for the removal of all those 

 substances which, arising incessantly in the animal system, can its solvent 

 not assume either the vaporous or gaseous state. In this con- P wer - 

 dition are the different saline bodies, such as the sulphates which are com- 

 ing from the destruction of the muscular tissues, as voluntary and invol- 

 untary motions are performed ; or the phosphates which are produced by 

 the destruction of cerebral and nervous 'matter. In the same condition 

 starid nearly all the nitrogenized results of the destruction of the soft 

 parts, and which are to a great extent to be removed as urea. Water dis- 

 solving with more or less facility these various bodies permits their escape 

 from the system by the secreting action of the kidneys, which, strain- 

 ing or filtering them from the blood, dismiss them to the bladder, from 

 which they are periodically removed. 



The skin is no inefficient auxiliary to the kidneys in effecting this re- 

 moval of water charged with soluble matters. All over its surface are 

 scattered in profusion the ducts of the perspiratory glands, which consist 

 of a convoluted tubing abundantly supplied with blood-vessels. The final 

 mode of action of these glands depends on extraneous circumstances. 

 Most commonly the fluid is carried away under the form of a vapor or in- 

 sensible perspiration, but when the secretion goes on more rapidly, or the 

 dew-point of the surrounding air is high, it then accumulates as drops of 

 sweat. The amount of water thus removed, even by insensible perspira- 



