288 PHYSIOLOGY. 



sily on each other. \Fat is also a secretion^ which is thrown 

 out in a fluid state, from the cellular tissue, into little cells'! 

 and it is mostly found immediately under the skin, between 

 that and the flesh. Its use seems to be, to lubricate the so. 

 lids and facilitate their movements ; to form a cushion around 

 the body, and protect it from external injuries as well as the 

 extremes of heat and cold. 



8. During sickness, when we take little or no food into 

 the stomach, Hife is supported by the absorption of the fat, 

 which is taken up by little vessels and again poured into the 

 blood^ to nourish the body ; also in animals which lie in 

 their burrows, in a half torpid state during the winter, their 

 nourishment is derived from the same source. 



Q.fMarrow which fills all the cavities of the long bones, 

 is very much like fat, and this also is a secretion from a thin, 

 delicate membrane, that lines the cavities of the bones^ 

 These are the principal internal exhalations, or secretions. 



10. The external secretions are two in number ; (/the first 

 and most important from the skin is called, when insensible, 

 perspiration ; and when it is visible, is called sweat ; the se- 

 cond is from the lungs, and can be seen in the form of a va- 

 pour in a frosty morning? The fluid which escapes from the 

 skin, is chiefly water, containing a little acid and some salts, 

 with a small quantity of animal matter. 



11. The skin is covered with an innumerable number of 

 pores, so small indeed, as to be invisible to the naked eye, 

 through which the insensible perspiration is constantly pour- 

 ing,amounting in weight to more than one half of all the 

 food and drink taken into the stomach, and much exceeding 

 that lost by all the other excretions^ 



12. From a vast number of experiments performed by dif- 

 ferent persons, it appears that the largest amount of insensi- 

 ble perspiration amounts to five pounds in twenty. four hours, 

 and the smallest to thirty-two ounces. Now, when we con. 

 sider that the skin, serves as one of the chief outlets, by 

 which the old and useless particles are got rid of, out of the 



