396 CHEMISTEY. 



559. How they Differ. Animal and vegetable chemistry 

 differ in several important particulars. The former is much 

 more complex and mysterious than- the latter. Certain 

 substances, as starch and sugar, found in such abundance 

 in some vegetables, are not present in animals in their 

 normal state. When taken into the animal they are 

 changed into fat and other substances. Then there is 

 not only difference but opposition between the chemical 

 action of leaves and that of lungs, carbon being given 

 out by lungs and taken in by leaves, and oxygen being 

 given out by leaves and taken in by lungs, as stated in 

 128. Besides all this, the plant lives upon unorganized 

 materials, while the animal lives upon organized materials 

 built up by the plant. 



560. The Blood. This universal building material of 

 the animal contains all the constituents needed for the 

 construction and repair of every part. There is fibrin, 

 out of which chiefly the various textures of the body are 

 formed. This is the firm part of the coagulum or clot 

 that separates when blood is left standing, there being in- 

 corporated with it the coloring matter of the blood. The 

 clot swims in a watery fluid called serum, which contains 

 albumen in solution. Besides these there is a variety of 

 materials in small amounts in the blood. There is iron, 

 which is contained in the matter which gives the blood its 

 red color. Then there are mineral materials for the manu- 

 facture of bones, teeth, etc., and various other substances. 

 Water constitutes about four fifths of the blood. Without 

 this the materials which we have mentioned could not be 

 carried to all parts of the body. In this they are sent to 

 their destination through innumerable tubes by the heart, 

 the great central pump of the circulation. 



561. How the Blood is Made. The blood is made mostly 

 from our food. We say mostly, because that important sub- 



