10 THE HUMAN BODY 



ditions of the elements contained in these compounds during their 

 sojourn inside the Body we know very little about; more especially 

 their state of combination during that part of their stay when they 

 do not exist dissolved in the bodily liquids, but form part of a more 

 or less compact living tissue. 



For present purposes the chemical compounds existing in or de- 

 rived from the Body may be classified as organic and inorganic, 

 and the former be subdivided into those which contain nitrogen 

 and those which do not. 



Inorganic Constituents. Of the simpler substances entering 

 into the structure of the Body the following are the most im- 

 portant : 



Water; in all the tissues in greater or less proportion and forming about 

 two-thirds of the weight of the whole Body. A man weighing 75 kilos (165 Ibs.), 

 if completely dried would therefore lose about 50 kilos (110 Ibs.) from the 

 evaporation of water. Of the constituents of the Body the enamel of the 

 teeth contains least water (about 2 per cent), and the saliva most (about 99.5 

 per cent) ; between these extremes are all intermediate steps bones contain- 

 ing about 22 per cent, muscles 75, blood 79. 



Common salt Sodium chlorid '(NaCl); found in all the tissues and 

 liquids, and in many cases playing an important part in keeping other sub- 

 stances in solution in water. 



Potassium chlorid (KC1); in the blood, muscles, nerves and most liquids. 



Calcium phosphate [CasCPO^l; in the bones and teeth in large quantity. 

 In less proportion in all the other tissues. 



Besides the above, ammonium chlorid, sodium and potassium phosphates, 

 magnesium phosphate, sodium sulphate, potassium sulphate, and calcium 

 fluoride have been obtained from the Body. 



Uncombined hydrochloric acid (HC1) is found in the gastric juice. 



Nitrogenous Organic Compounds. These fall into several main 

 groups : proteins * subdivided into simple proteins, conjugated pro- 

 teins, and derived proteins nitrogenous extractives, and pigments. 

 The interesting substances known as enzyms probably form like- 

 wise a group under this head. 



Simple Proteins. Under this head are grouped those proteins 

 whose molecules contain only protein material; in contradistinc- 



* The classification of proteins here given is that recommended by the joint 

 committee on protein nomenclature of the American Physiological Society 

 and the American Society of Biological Chemists, 1907. 



