CHAPTER XXV 



THE CHEMICAL COMPOSITION OF THE BODY 



THE body is built up of a large number of chemical elements, which 

 are in most instances united together into compounds. 



The elements found in the body are carbon, nitrogen, hydrogen, 

 oxygen, sulphur, phosphorus, fluorine, chlorine, iodine, silicon, sodium, 

 potassium, calcium, magnesium, lithium, iron, and occasionally traces 

 of manganese, copper, and lead. 



Of these very few occur in the free state. Oxygen (to a small 

 extent) and nitrogen are found dissolved in the blood ; hydrogen is 

 formed by putrefaction in the alimentary canal. With some few 

 exceptions such as these, the elements enumerated above are found 

 combined with one another to form what are called compounds. 



The compounds, or, as they are generally termed in physiology, 

 the proximate principles, found in the body are divided into 



(1) Mineral or inorganic compounds. 



(2) Organic compounds, or compounds of carbon. 



The inorganic compounds present are water, various acids (such 

 as hydrochloric acid in the gastric juice), ammonia (as in the urine), 

 and numerous salts, such as calcium phosphate in bone, sodium chloride 

 in blood and urine, and many others. 



The organic compounds are more numerous ; they may be sub- 

 divided into 



CProteids e.g. albumin, myosin, casein. 

 XT ., J Albuminoids e.g. gelatin, elastin. 



1 ' ^ Simpler nitrogenous bodies e.g. lecithin, 



\ creatine. 



(Fats e.g. butter, fats of adipose tissue. 

 VT ., I Carbohydrates e.g. sugar, starch. 



Non-nitrogenous , Simple y orffanic b o d i es -e.g. cholesterin, lactic 



I. acids. 



The subdivision of organic proximate principles into proteids, fats, 

 and carbohydrates forms the starting-point of chemical physiology. 



Carbohydrates. 



The Carbohydrates are found chiefly in vegetable tissues, and 

 many of them form important foods, Some carbohydrates are, how- 



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