THE NATURE AND AMOUNT OF PERSPIRATION. 431 



Since there are in man no goblet cells in the vesical epithelium (in the frog 

 they are present) or mucous glands in the walls of the bladder, this mucus 

 must be supplied by an abnormal metabolism of the ordinary epithelial 

 cells. 



THE NATURE AND AMOUNT OF PERSPIRATION. 



366. The quantity of matter which leaves the human body by way 

 of the skin is very considerable. Thus, it has been estimated that while 

 0.5 gramme passes away through the lungs per minute, as much as 0.8 

 gramme passes through the skin. The amount, however, varies extremely ; 

 it has been calculated, from data gained by enclosing the arm in a caout- 

 chouc bag, that the total amount of perspiration from the whole body in 

 twenty-four 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 vapor 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 insen- 

 sible to the sensible perspiration will depend on the rapidity of the secre- 

 tion in reference to the dryness, temperature, and amount of movement of 

 the surrounding atmosphere. Thus, supposing the rate of secretion to 

 remain constant, the drier and hotter the air, and 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 perspira- 

 tion only, it may, and frequently does, happen that we seem to ourselves to 

 be perspiring freely, when, in reality, it is not so much the total perspira- 

 tion which is being increased as the relative proportion of the sensible per- 

 spiration. 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 increase of the secretion, and it is possible that mere 

 dryness of the air has a similar effect. 



The amount of perspiration given off is affected not only by the condition 

 of the atmosphere, but also by the circumstances of the body. Thus it is 

 influenced by the nature and quantity of food eaten, by the amount of fluid 

 drunk, by the character of exercise taken, by the relative activity of the 

 other excreting organs, more particularly of the kidney, by mental condi- 

 tions, and the like. Variations may also be induced by drugs and by dis- 

 eased conditions. How these various influences produce their effects we shall 

 study immediately. 



The fluid perspiration, or sweat, when collected, is found to be a clear, 

 colorless fluid of a distinctly salt taste, with a strong and distinctive odor, 

 varying according to the part of the body from which it is taken. Besides 

 accidental epidermic scales, it contains no structural elements. 



Sweat, as a whole, is furnished partly by the sweat-glands and partly by 

 the sebaceous glands, for, as we shall see, the small amount which simply 

 transudes through the epidermis, apart from the glands, may be neglected. 

 Now, the secretions from these two kinds of glands differ widely in nature, 

 and the characters of the sweat, as a whole, will vary according to the rela- 



