CHEMISTRY OF THE HUMAN BODY. 57 



tuent part of albumen, fibrin, gelatine, and mucus. Oxygen 

 is derived partly from the air we breathe, and partly from 

 our food and drinks. It is given off in all the secretions 

 and excretions. The air contained in the swimming bladder 

 of fishes, is pure oxygen. 



4. ^Hydrogen exists in all the fluids and most of the solids, 

 constituting as it does one element of water. In venous 

 blood, it exists in a larger proportion than in arterial blood, 

 which contains more oxygen. In the bile, it is very abund- 

 ant, and in fat and oil, is one of the essential elements. It 

 is this gas which often causes so much distress in a weak 

 state of the stomach. Hydrogen is introduced into the 

 system by means of food and drinks, and is discharged in 

 the same manner as oxygen^ 



5. {Carbon abounds in the vegetable as well as animal 

 kingdom. In oil, fat, albumen, gelatine, fibrin, and mucus, 

 it always forms a part. In bile, and in venous blood, it 

 exists largely. If we burn a piece of animal substance, 

 what is left is found to be chiefly carbon. We obtain it 

 from our food, and give it off by breathing and the secretions. 

 It is carbon that makes venous blood darker than arterial, 

 and the change from purple to bright crimson which takes 

 place in the lungs, id supposed to be owing chiefly to the 

 fact, that the excess of carbon contained in venous blood is 

 discharged by respirationj 



Q.^Azote exists in large quantities in all animal matter. 

 It also exists to some extent in a few vegetables, but it is an 

 essential element in animal substances. It is more abund- 

 ant in fibrin, of which the muscular flesh is chiefly formed, 

 than in any other portions of the body, though it is found 

 in the brain and nerves. The peculiar smell of burning 

 animal matter is owing to azote. When animal substances 

 putrefy, it combines with hydrogen, and forms ammonia or 

 hartshorn^ 



7. Azote is chiefly taken into the system by means of 

 animal food. It is also taken into the blood by respiration, 



