1 8 HUMAN PHYSIOLOGY 



fluids. In the coagulation of blood it is supposed to aid in 

 the formation of fibrin-ferment. 



10. Magnesium carbonate and magnesium phosphate 

 are present in the bones and often accompany the calcium 

 salts, but in smaller quantities. Only in the muscles and in 

 the thymus does the magnesium phosphate exceed the 

 corresponding calcium salt. 



11. In smaller quantities and without any known physiological 

 importance are the following: Potassium carbonate, the secondary 

 sodium phosphate, sodium sulphate, potassium sulphate, magnesium 

 sulphate, calcium fluoride (in bones and enamel of teeth). 



2. THE ORGANIC ENERGY-YIELDING COMPOUNDS OF 



THE BODY 



A physiological principle according to which the following 

 substances maybe grouped is not yet known, as our knowl- 

 edge of the role of each one in metabolism is still too 

 limited. We may classify them from a chemical standpoint 

 as follows : 



i. Carbohydrates; 2. Fats; 3. Proteids. 



i. The carbohydrates derive their name from the fact 

 that, besides carbon, they contain hydrogen and oxygen in 

 the same proportion as water. This characteristic has no 

 reference to the chemical constitution of the substances. 



The carbohydrates are aldehydes or ketones of hexatomic 

 alcohols or anhydrid unions of two or more molecules of 

 such aldehydes and ketones. Their number of carbon 

 atoms is six or a multiple of six. 



Heating changes all carbohydrates to caramel having a 

 characteristic odor ; they are all stained red by thymol and 

 concentrated sulphuric acid. 



They are classified as : 



Monosaccharides. . . C,H 10 O 



o \.2t o ' 



Disaccharides C 12 H 29 O n ; 



Polysaccharides C,.H 10 O 5 . 



The monosaccharides and disaccharides are also called 

 sugars; they have a more or less sweet taste, the disac- 



