22 PKINCIPLES OF VETEH1NARY SCIENCE 



Pigments of the body are nitrogenous in nature. They are 

 found in the body and milk fats, the skin, hair, horn, eye, and 

 pathologically in the melanotic tumors so common in white and 

 gray horses. Chemically the natural yellow pigments of the 

 animal body are similar to and derived from the yellow vegetable 

 pigments found accompanying chlorophyl in all green plants. 



Nitrogenous fats are represented by lecithin, a complex com- 

 pound containing a relatively large amount of phosphorus. 



Amino-acids are the simple nitrogenous bodies, derived from 

 the proteins of digested foods, that are found in the circulating 

 blood and tissue fluids. They are available for use by the animal 

 to build up its protoplasm. 



Urea and uric acid belong to a group of nitrogenous waste 

 compounds found in the excreta of the body. 



(2) The non-nitrogenous substances are fats and various 

 carbohydrates. It is evident that no nitrogen is present in their 

 molecules. 



Fats contain the elements carbon, hydrogen, and oxygen. The 

 latter is present in very small percentage. Neither hydrogen nor 

 oxygen is present in the proportion to form water. The princi- 

 pal animal fats are stearin, palmitin, and olein. They are derived 

 from both animal and vegetable fats consumed as food. Chemi- 

 cally, fats are esters of glycerol and the fatty acids. 



Carbohydrates contain the same elements as fats but in simpler 

 combinations. They occur chiefly as monosaccharids, disac- 

 charids, and polysaccharids. A member of the first group found 

 in the animal body is dextrose. Lactose, or milk sugar as it is 

 commonly called, is a constituent of milk and belongs to the 

 group of disaccharids. The more highly organized polysac- 

 charids of the body are represented by glycogen, or animal starch. 

 It is found in the liver, muscles, and other tissues and occurs in 

 large quantities in all fetal tissues. Carbohydrates are used by 

 the body to furnish energy. 



THE CELLS OF THE ANIMAL BODY 



In a well planned system of education the simplest subjects 

 are taken up first to prepare the student for the more complex 

 that are to follow. This plan will be followed in our study of 

 the structure of the animal body, and will start with the smallest 

 structural unit of life — the cell. 



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