354 PHYSIOLOGICAL CHEMISTRY. 



dioxide, water, ammonia, sulphates, phosphates, etc. This de- 

 composition of a dead body is generally a simultaneous fermen- 

 tation or putrefaction, aided by decay or slow combustion. 



There are numerous intermediate products formed, which 

 differ according to the nature of the decomposing substance, or 

 according to the conditions (degree of temperature, amount of 

 moisture and air present, etc.) under which the decomposition 

 takes place. 



During the decomposition of dead vegetable matter (especi- 

 ally of moist wood) the intermediate products are frequently 

 called humus, which substance (or better mixture of substances) 

 forms the chief part of the organic matter in the soil. 



During the decomposition of dead animals, the sulphur is 

 first eliminated as hydrosulphuric acid, and a number of other 

 intermediate products have been shown to be formed ; among 

 them certain organic bases often called ptomaines or cadaveric 

 alkaloids, substances which have poisonous properties. The de- 

 composition of organic matter maj T be prevented under condi- 

 tions which have been mentioned heretofore in connection with 

 putrefaction. 



QUESTIONS. 



491. What is the difference between vegetable and animal life in a 

 chemical point of view ? 



492. Mention the chief substances serving as plant food. 



493. Explain the formation of organic substances in the plant. 



494. What elements enter into the animal system as necessary con- 

 stituents? 



495. The members of which three groups of organic substances are 

 chiefly used as food by animals? 



496. Which substances are generally termed "nutritive," and which 

 "heat-giving?" 



497. Explain the chemical change which food suffers during digestion. 



498. Mention the four principal fluids which are secreted by various 

 organs of the animal body, in order to facilitate or cause digestion. 



499. What are the waste products of animal life, and through which 

 channels are they eliminated? 



500. What is the final result of the decomposition of dead plants or 

 animals ? 



