122 LIFE IN THE SEA [CH. 



the carbon and hydrogen which they contain leave 

 the body in the form of carbonic acid and water, 

 mainly from the lungs and kidneys. The proteid is 

 also oxidised or decomposed and most of its carbon 

 and hydrogen also leave the body in the form of 

 carbonic acid and water, but the nitrogen part of the 

 molecule is not completely degraded. Carbonic acid 

 and water are compounds which are fully oxidised 

 and can no longer be used to yield energy but the 

 product of the nitrogenous metabolism is either urea, 

 or uric acid, or some other analogous substance which 

 is not fully oxidised and can still supply energy. 

 With the exception of these nitrogen compounds the 

 clock has run down. 



When an animal or plant dies the substance of its 

 body becomes degraded so that the ultimate products 

 of decomposition are water, carbonic acid, nitric acid, 

 sulphuretted hydrogen and a few other substances. 

 This resolution of the organic body is effected by the 

 agency of a number of species of bacteria. The 

 proteids are attacked by the putrefactive micro- 

 organisms which first of all reduce them to the form 

 of amino-acids just as in the case of digestion. The 

 fats and carbohydrates are attacked by the fermenta- 

 tive micro-organisms which reduce them ultimately 

 to the form of carbonic acid and water. Some of the 

 microbes of fermentation and putrefaction act with 

 the assistance of oxygen (aerobic bacteria), while 



