PART III 



THE ANIMAL 



CHAPTER XVII 



THE CHEMISTRY OF ANIMAL PHYSIOLOGY 



The highest and most complex products of the farm are 

 animals (Fig. 74). Directly or indirectly animals are de- 

 pendent on plants for their sustenance. There are, of 

 course, many obvious differences between plants and animals, 

 but they are both living things that reproduce themselves. 

 They are composed largely of carbon compounds; that is, 

 they are organic in nature. For the proper elaboration of 

 these compounds, a few elements are necessary. But, 

 whereas plants absorb soluble inorganic compounds and 

 from them build up their tissue, animals must have organic 

 food material previously elaborated by plants. This material 

 is taken into the animal and made soluble before being 

 absorbed and rebuilt into animal tissue. 



224. Essential Elements for Animals.— For animals there 

 are needed in compound form the following fifteen elements : 

 Carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, 

 sulphur, calcium, iron, magnesium, sodium, chlorine, iodine, 

 silicon, and fluorine. It is to be noted that the last five 

 elements, while essential for animals, are not essential for 

 plants. 



225. Composition of the Animal. — Like the plant, the 

 animal is composed largely of water, but not to so great an 

 extent. The average amount of water in farm animals is 

 not far from 50 per cent. In man it is about 70 per cent. 

 Of the drv matter of steers 60 per cent, is carbon, 14 per 



