188 FIRESIDE SCIENCE. 



perspiration is propelled around the tube several 

 times before it is ejected. Now, we are talking 

 about small things ; but so long as we confine our 

 descriptions to a single duct, we utterly fail to real- 

 ize their minuteness. Let us look at them collec- 

 tively. On every square inch' of the palm of your 

 hand, reader, there are at least 3,500 of these per- 

 spiratory ducts. Each one of them being one 

 quarter of an inch long, we readily see that every 

 square inch of skin surface on this part of the body 

 has 73 feet of tubing, through which moisture and 

 effete matter are constantly passing, night and day. 

 The ducts, however, are shorter elsewhere ; and it 

 will be fair to estimate 60 feet as the average 

 length of the ducts for each square inch of the 

 body. This estimate (reckoning 2,500 square inches 

 of surface for a person of ordinary size) gives for 

 these ducts an aggregate length of 28 miles. 



The amount of liquid matter which passes 

 through these microscopical tubes in twenty-four 

 hours, in an adult person of sound health, is about 

 sixteen fluid ounces, or one pint. One ounce of 

 the sixteen is solid matter, made up of organic and 

 inorganic substances which, if allowed to remain in 

 the system for a brief space of time, would cause 

 death. The rest is water. Beside the water and 

 solid matter, a large amount of carbonic acid, a 

 gaseous body, passes through the tubes ; so we can- 



