SEC. 6. THE NATURE AND AMOUNT OF PERSPIRATION. 



438. The quantity of matter which leaves the human body 

 by way of the skin is very considerable. Thus it has been estimated 

 that while '5 gram passes away through the lungs per minute, as 

 much as *8 gram passes through the skin. The amount, however, 

 varies extremely; it has been calculated, from data gained by 

 enclosing the arm in a caoutchouc bag, that the total amount of 

 perspiration from the whole body in 24 hours might range from 

 2 to 20 kilos ; but such a mode of calculation is obviously open to 

 many sources of error. 



Of the whole amount thus discharged, part passes away at 

 once as watery vapour mixed with volatile matters, while part may 

 remain for a time as a fluid on the skin ; the former is frequently 

 spoken of as insensible, the latter as sensible perspiration or sweat. 

 The proportion of the insensible to the sensible perspiration will 

 depend on the rapidity of the secretion in reference to the dryness, 

 temperature and amount of movement of the surrounding atmo- 

 sphere. Thus, supposing the rate of secretion to remain constant, 

 the drier and hotter the air, and the more rapidly the strata of air 

 in contact with the body are renewed, the greater is the amount of 

 sensible perspiration which is by evaporation converted into the 

 insensible condition; and conversely when the air is cool, moist, and 

 stagnant, a large amount of the total perspiration may remain on 

 the skin as sensible sweat. Since, as the name implies, we are 

 ourselves aware of the sensible perspiration only, it may and 

 frequently does happen that we seem to ourselves to be perspiring 

 largely, when in reality it is not so much the total perspiration 

 which is being increased as the relative proportion of the sensible 

 perspiration. The rate of secretion may, however, be so much 

 increased, that no amount of dryness, or heat, or movement of the 

 atmosphere, is sufficient to carry out the necessary evaporation, and 

 thus the sensible perspiration may become abundant in a hot, dry 

 air. And practically this is the usual occurrence, since certainly 

 a high temperature conduces, as we shall point out presently, to an 



