ANIMAL FLUIDS AND TISSUES. 649 



There is also excretion through the intestinal tract. 



Chemical changes after death. After the death of either a 

 plant or an animal, a chemical decomposition commences which finally 

 results in the formation of those inorganic compounds from which 

 the plant originally derived its food, viz., carbon dioxide, water, 

 ammonia, sulphates, phosphates, etc. This decomposition of a dead 

 body is generally a simultaneous fermentation 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 (especially 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 hydrogen sulphide, and a number of other intermediate 

 products have been shown to be formed ; among them certain organic 

 bases called ptomaines or cadaveric alkaloids, substances which have 

 been spoken of in Chapter 52. The decomposition of organic matter 

 may be prevented under conditions which have been mentioned here- 

 tofore in connection with putrefaction. 



55. ANIMAL FLUIDS AND TISSUES. 



Constituents of the animal body. The animal body consists 

 mainly of three kinds of matter, viz., water, organic, and inorganic 

 matter. It contains of water about 70 per cent., of organic matter 

 25 per cent., and of inorganic matter about 5 per cent. The water 

 may be determined by drying a weighed quantity in an air-bath at a 

 temperature of 100 to 105 C. (212-221 F.); the organic matter 

 is estimated by burning the dried substance, and the inorganic matter 



QUESTIONS. What is the difference between vegetable and animal life from 

 a chemical point of view ? Mention the chief substances serving as plant food. 

 Explain the formation of organic substances in the plant. What elements 

 enter into the animal system as necessary constituents? The members of which 

 three groups of organic substances are chiefly used as food by animals? Give 

 a full explanation of respiration. Explain the term calorie, and state the use 

 made of it in valuation of food. Which points should be considered in the 

 selection of a diet? What are the waste products of animal life, and through 

 which channels are they eliminated? What is the final result of the decom- 

 position of dead plants or animals ? 



