22 THE HOBSE IN HEALTH AND DISEASE 



of heat. A fat animal, therefore, needs less food than a lean one to 

 niaintain itself. 



Carbohydrates occur chiefly as monosaccharids, disaccharids, 

 and polysaccharids. Milk-sugar or lactose is a constituent of 

 milk and belongs to the group of disaccharids. The more highly 

 organized polysaccharids are represented by glycogen, or animal 

 starch. It is found in the liver, muscles, and other tissues of the 

 body and occurs in large quantities in all fetal tissues. 



The animal body contains about 56 per cent, water, 21 per cent, 

 fat, 18 per cent, protein, and 5 per cent. .ash. From these figures 

 it will be seen that water is present in the largest percentage of any 

 of the constituents of the body. An analysis of the composition of 

 the body of the horse is not available. The Rothamsted Station 

 has determined the percentage composition of the whole bodies of 

 the pig, calf, ox, and sheep both in fat and half-fat conditions. 

 On the strength of this work it may be concluded that the young 

 growing horse requires a plentiful supply of protein and ash to 

 make the most economical gain, while a mature horse can be main- 

 tained on a ration containing relatively smaller amounts of these 

 substances. 



THE CELLS OF THE ANIMAL BODY 



The body is composed of countless millions of microscopic 

 elements called cells. The cell is the smallest unit of life. Cells 

 are grouped together to form, first, the tissues, which in turn form 

 the various organs of the body. To understand the numerous 

 functions of the intact body the cellular structure must be studied. 

 This can only be done satisfactorily with the aid of a microscope, 

 so is beyond the scope of this book. 



By way of introduction to the study of histology, it may be 

 stated that all typical animal cells have certain characteristics 

 (Fig. 1). Each possesses a cell body or protoplasm, a cell nucleus 

 or germ center, and a nucleolus. Most of them also have a cell 

 wall to confine the essential parts just mentioned. 



Protoplasm is the material basis of the cell and the life processes. 

 It is a transparent, viscid substance to the sight and touch. On 

 close examination it is found to be a complex mass of organic 

 material held together by a very delicate mesh work of fibers. In 

 plants and animals protoplasm is essentially the same. 



Three well-known physical forces operate in living protoplasm. 



