12 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



energy ; and finally the simple products of oxidation or chemical 

 breakdown are carried to the organs of excretion (lung, skin, kidney, 

 &c.), where they are discharged from the body. 



A candle consists principally of carbon and hydrogen ; when it is 

 burnt the products are carbonic acid gas and water ; the former may 

 be detected by means of lime water, the latter, by holding a dry 

 beaker upside down for a few moments over the burning candle, when 

 the moisture will condense on the cold glass. 



The body is more complex than a candle, but so far as its carbon 

 and hydrogen are concerned the main products of combustion are 

 the same. The carbon dioxide is discharged by the expired air, as 

 may be proved by blowing it into lime water. The water finds an 

 outlet by several channels, lungs, skin, and kidneys. The presence of 

 nitrogen in the body is perhaps the most striking chemical distinction 

 between it and a candle, and here again the process of metabolism 

 runs a course analogous in some degree to our experiments in vitro. 

 Here again the most important and abundant substance which 

 contains the waste nitrogen is the simple material ammonia, but 

 ammonia is only discharged as such to a very small extent in health. 

 It unites with carbon and oxygen to form the body called urea 

 (CON 2 H 4 ), which finds its way out of the body via the urine. The 

 urine also contains the sulphates, due to the oxidation of the sulphur 

 of the proteins, and the phosphates due to the similar oxidation of 

 the phosphorus of such substances as lecithin and nuclein. Some 

 of the salts of the urine, however, in particular the chlorides, come 

 directly from the food. This we shall discuss at the proper place 

 when we come to the study of the urine. 



