54 PRINCIPLES OF ANIMAL BIOLOGY 



from the flesh of their prey and young mammals get vitamines from the 

 milk with which they are nourished. 



Further Characteristics of Carbohydrates, Fats, and Proteins. — An 

 examination of the chemical formulas for carbohydrates stated in the 

 paragraph on photosynthesis shows, as indicated also in part in the pre- 

 ceding chapter, that carbohydrates are composed of carbon, oxygen and 

 hydrogen; and the hydrogen and oxygen are generally in the ratio of 2 to 1, 

 as in water. Sugars as they occur in fruits and vegetables and in manu- 

 factured form, and starches as they occur in flour and in some fleshy 

 roots, stems and fruits are good examples of carbohydrates. Carbo- 

 hydrates burn (oxidize) readily with the release of considerable heat, and 

 the liberation of carbon dioxide and water. 



Fats are composed of carbon, hydrogen, and oxygen but as indicated 

 above the ratio of oxygen to hydrogen is very low and the proportion of 

 carbon is high. The character of a fat is determined by the fatty acid 

 or acids entering into the composition. Fats are greasy and they leave 

 a grease-spot on paper which does not evaporate. Good examples of 

 fats are butter, lard and tallow derived from animal sources, and oils, 

 such as olive, castor and cocoanut oils derived from plants. Fats com- 

 bine readily with oxygen when burned and yield much more heat than do 

 the carbohydrates. Thus a gram of starch yields about 4.19 large 

 calories, while a gram of fat yields about 9.3 large calories. The products 

 of the combustion of fats are carbon dioxide and water. 



Proteins are always composed of carbon, oxygen, hydrogen, and 

 nitrogen, and sometimes one or more other elements as phosphorus, 

 iron, magnesium, sulphur, etc. The protein molecule is very complex. 

 For this reason the analysis of proteins is very difficult and there may be 

 considerable disagreement as to the empirical formula of the same protein. 

 Two formulas for hemoglobin, a protein derived from the blood cor- 

 puscles, are C7i2Hii3oN2i40245FeS2, and C6ooH96oNi540i79FeS2. Needless 

 to say that the structural formulas cannot be given. Proteins co- 

 agulate upon heating or upon the addition of acids, alcohol or salts to 

 form a firm clot which often is not soluble in water. The coagulum 

 produced by neutral salts is soluble. Proteins have a large molecular 

 weight, slow diff usibility, and high resistance to the passage of an electric 

 current. Proteins burn with the release of considerable heat, and in- 

 complete burning is accompanied by the production of a characteristic 

 odor. The products of combustion are carbon dioxide, water, and certain 

 nitrogenous compounds. White of egg, lean meat, and gluten derived 

 from wheat are good examples of proteins. Seeds of leguminous plants 

 and nuts are rich in proteins. 



Digestion. — Living matter, be it plant or animal, cannot make use of 

 foods until these foods have been rendered soluble and diffu.sil)le through 

 protoplasm. In the plant cell starch, before it can be utilized in building 



