CHEMISTRY OP THE BODY. 9 



Elements Composing the Body. Of the elements known 

 to chemists only sixteen have been found to take part in 

 the formation of the human Body. These are carbon, hy- 

 drogen, nitrogen, oxygen, sulphur, phosphorus, chlorine, 

 fluorine, silicon, sodium, potassium, lithium, calcium, 

 magnesium, iron, and manganese. Copper and lead have 

 sometimes been found in small quantities but are probably 

 accidental and occasional. 



TJncombined Elements. Only a very small number of 

 the above elements exist in the bodyuncombined. Oxygen 

 is found in small quantity dissolved in the blood; but even 

 there most of it is in a state of loose chemical combination. 

 It is also found in the cavities of the lungs and alimentary 

 canal, being derived from the inspired air or swallowed 

 with food and saliva; but while contained in these spaces 

 it can hardly be said to form a part of the Body. Nitro- 

 gen also exists uncombined in the lungs and alimentary 

 canal, and in small quantity in solution in the blood. Free 

 hydrogen has also been found in the alimentary canal, be- 

 ing there evolved by the fermentation of certain foods. 



Chemical Compounds. The number of these which 

 "may be obtained from the Body is very great; but with re- 

 gard to very many of them we do not know that the form 

 in which we extract them is really that in which the ele- 

 ments they contain were united while in the living Body; 

 ;since the methods of chemical analysis* are such as always 

 break down the more complex forms of living matter and 

 leave us only its debris for examination. AYe know in 

 fact, tolerably accurately, what compounds enter the Body 

 iis food and what finally leave it as waste; but the inter- 

 mediate conditions of the elements contained in these com- 

 pounds during their sojourn iriside the Body we know very 

 little about; more especially their state of combination dur- 

 ing that part of their stay when they do not exist dissolved 

 in the bodily liquids, but form part of a solid living 

 tissue. 



For present purposes the chemical compounds existing 

 in or derived from the Body may be classified as organic 



