THE CHEMICAL COMPOSITION OF THE BODY. [CH. xxv. 



gases. A 100 c.c. measuring-tube graduated in tenths of a cubic centimetre 

 between 75 and 100 ; a filling bulb (A) and two gas pipettes are connected 

 up as in the diagram (fig. 335). 



It is first charged with acidulated water up to the zero mark by raising 

 the filling bulb, tap i being open. It is then filled with 100 c.c. of expired 

 air. the filling bulb biiing lowered till the fluid in the tube has fallen to the 

 100 mark. Tap i is now closed. The amount of carbonic acid in the expired 

 air is next ascertained ; tap 2 is opened, and the air is expelled into the gas 

 pipette containing strong caustic potash solution by raising the filling bulb 

 until the fluid has risen to the zero mark of the measuring tube. Tap 2 is 

 closed, and the air left in the gas pipette for a few minutes, during which the 

 carbonic acid is absorbed by the potash. Tap 2 is then opened and the air 

 drawn back into the measuring tube by lowering the filling bulb. The 

 volume of air (jDiinus the carbonic acid) is read, the filling bulb being 

 adjusted so that its contents are at the same level as the fluid in the 

 measuring tube. The amount of oxygen is next ascertained in a precisely 

 similar manner by sending the air into the other gas pipette, which contains 

 sticks of phosphorus in water, and measuring the loss of volume (due to 

 absorption of oxygen) in the air when drawn back into the tube. 



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 physio- 

 logy, 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 

 subdivided into 



