12 THE HUMAN BODY. 



mediate stages between the proteids which enter the body and 

 the urea and uric acid which leave it. 



In the bile or gall, two crystallizable nitrogen-containing 

 bodies, glycocholic and taurocholic acid, are found combined 

 with soda. 



Nitrogenous Coloring Matters. These form an artificial 

 group whose constitution and origin are ill known. Among 

 the most important are the following: 



Hcematin, derived from the red corpuscles of the blood in 

 which a residue of it is combined with a proteid residue to 

 form haemoglobin. 



Bilirubin and liliverdin, which exist in the bile; the 

 former predominating in the bile of man and of carnivorous 

 . animals and giving it a reddish-yellow color, while biliverdin 

 predominates in the bile of Herbivora, which is green. 



Non-Nitrogenous Organic Compounds. These may be 

 conveniently grouped as hydrocarbons or fatty bodies; carbo- 

 hydrates or amyloids / and certain non-azotized acids. 



Pats. The /ate all contain carbon, hydrogen and oxygen, 

 the oxygen being present in small proportion as compared 

 with the hydrogen. TTlT1 fifl , fqfg npf> ip- *'" ^^ ^oriy in large 

 qnantities 1 vig^ palmatin (C^H^O,.'). stearin (C B ,H 1I0 6 ), 

 fl,i)rl nlp ; ip_^r^ H |u ( }j. The two fanner when pure are solid 

 at the temperature of the Body, but in it are mixed with 

 olein (which is liquid) in such proportions as to be kept fluid. 

 The total quantity of fat in the Body is subject to great vari- 

 ations, but its average quantity in a man weighing 75 kilo- 

 grams (165 pounds) is about 2.75 kilograms (6 pounds). 



Each of these fats when heated with a caustic alkali, in 

 the presence of water, breaks up into a fatty acid (stearic, 

 palmitic or oleic as the case may be), and glycerin. The 

 fatty acid unites with the alkali present to form a soap. 



Carbohydrates. These also contain carbon, hydrogen 

 and oxygen, but there is one atom of oxygen present for 

 every two of hydrogen in the molecule of each of them. 

 Chemically they are related to starch. The more important 

 of them found in the Body are the following: 



Glycogen (G^H^OJ, found in large quantities in the liver, 

 where it seems to be a reserve of material answering to the 

 starch stored up by many plants. It exists in smaller quanti- 

 ties in the muscles. 



Glucose, or grape-sugar (C 6 H ]2 6 ), which exists in the 



