104 THE HUMAN SOD 7. 



der to keep us alive, oxygen is really a food as much as any 

 of the other substances which we take into our bodies 

 from outside, in order to keep them alive and at work. 

 Suffocation, as death from deficient air supply is named, is 

 really death from oxygen-starvation. 



What is suffocation? 



APPENDIX TO CHAPTER VIII. 



The liberation of energy by oxidation, or burning, at a low tem- 

 perature and in the presence of moisture, is such a fundamental fact 

 in physiology, and its essential agreement with ordinary combustion 

 so difficult to grasp by most pupils, who naturally associate burning 

 with a high temperature and luminosity, that it is worth while to il- 

 lustrate these facts by a few simple experiments. 



1. Buy a coil of magnesium wire, which can be obtained at small 

 cost. Rub it clean with fine emery paper : cut it in two, apply a 

 lighted match to one half and show how it is rapidly consumed with 

 the evolution of light and heat, leaving behind only a white powder, 

 magnesia, which is oxidized magnesium. Put the other half away in 

 a bottle with a few drops of water. After a day or two its surface 

 will be covered by a layer of magnesia; if this be scraped off another 

 will succeed it ; and so on. This experiment shows that oxidation 

 may occur rapidly at a high temperature in a short time, or slowly 

 at a low temperature in a long time, but the ultimate product, in each 

 case, is the same. 



2. In relation to a subsequent paragraph (p. 112) the magnesia ob- 

 tained by burning the wire in the air, may be kept, and attempts 

 made to ignite it: this will serve to show the uselessness of oxidized 

 substances to the body, as sources of energy : they cannot be any 

 more oxidized, and the best thing to do is to get rid of them. 



8. Get a bundle of iron wire : rub it bright with emery or sand 

 paper. Place some in a warm dry bottle by the stove or fireplace. 

 Put the rest in a bottle containing a little water. Next day the first 

 specimen will be found bright, and the second covered with rust. This 

 shows that oxidation may sometimes occur better in the presence of 

 water than in its absence ; and serves as a text for pointing out how 

 oxidations occur in the moist tissues of the body. 



