BAD AIR AND BAD HEALTH. 817 



meable walls of these minute vessels, batliing and feeding the 

 whole surrounding tissue. Thus, as somebody has said, the whole 

 of the new and living body is in solution in this wonderful food- 

 stream of the blood, which, by a very subtle mechanism of nerves, 

 distributes its good gifts in proportion to the needs of each sepa- 

 rate part. But the blood is not simply a food-stream, it is also a 

 sewage-stream, and it is as such that we are specially interested 

 in it. Where no growth or storing of flesh material of any kind 

 is taking place in the system, it is evident that that part of the 

 daily food which is turned into tissue measures not only the daily 

 construction that is taking place within us, but also the daily de- 

 struction or waste. In fact we — if we may so speak of the parti- 

 cles of which we are composed — are forever living and dying 

 within ourselves — making a new self, and getting rid of an old 

 self ; and just as the new living body is in solution in the blood, 

 so also is the old dead body, that has done its work and has to be 

 got rid of. Now, of this dead body a large part has to escape 

 through our lungs and through our skin. 



About this process of waste very little is known. "We know, 

 while certain temporary forms of waste are found in muscle, such 

 as kreatin (Gr. Tcreas, flesh), which, whether again made use of 

 or not (M. Foster, page 154), is supposed to be eventually changed 

 in some complex manner into urea in the liver (M. Foster, page 

 755), and an acid called sarcolactic (Gr. sarx, flesh ; gala, milk), 

 which is also supposed to be decomposed in the liver into car- 

 bonic acid and water (M. Foster, page 836), that all our dead tis- 

 sue is, with a certain slight but most important exception, got rid 

 of safely at last, as urea, carbonic acid, and water.* These are 

 the final forms which the waste that passes from the tissue into 

 the blood takes — the urea being separated from the blood and got 

 rid of by the kidneys, the carbonic acid both by the skin and the 

 lungs, and the water by all three channels of separation. f 



But we said that urea, carbonic acid, and water did not ac- 

 count for quite all the waste tissue ; and among the part not so 

 accounted for are the very hurtful poisons which escape from 

 lungs and skin. What are these poisons ? Have they a connec- 

 tion with or a resemblance to the poisons which, as we know, ex- 

 ist at all times within the system on a large scale. Dead or waste 

 tissue probably passes through many forms before it reaches the 

 safe final forms of carbonic acid and water, and we must conclude 



* We are not taking into account certain other substances discharged from the skin 

 in small quantities. 



\ " The natural waste of the body appears in two simple forms of carbonic acid — the 

 gaseous form having the chemical formula C0,0, while that which is got rid of in solution 

 is urea, that is, C0,(NH2)', in which the second atom of oxygen in the carbonic acid is re- 

 placed by a nitrogenous body termed amidogen." — (L. P.) 

 VOL. XL. — 55 



