ANIMAL STRUCTURE AND FUNCTION. IJ 



They are constantly in action, and even when the body is at rest there 

 is a very slight perspiration from them, though not sufficient to be visible. 

 The hairs are produced from the hair bulbs, which also are deep in the skin, 

 and they make their exit at such an acute angle with the surface that the 

 coat lies flat and smooth. The coat is shed twice yearly, m spring and 

 autumn, and replaced by a finer or thicker growth suitable to the season, 

 while throughout the year there is a constant slight shedding of old and 

 growth of new hair. Each hair has a muscle, which when in action 

 can pull it into an upright position, and on each side of each hair is 

 attached a small oil gland, the produce of which is exuded at the base of 

 the hair and greases it. The scurf skin (epidermis) acts the part of a 

 protective layer to the too sensitive structures underneath ; the sweat 

 helps to regulate the body temperature and get rid of some of the waste 

 products caused by exertion ; the coat provides warmth, and the oil glands, 

 by greasing the hairs, give them polish and render the whole surface water- 

 proof. The skin generally is very elastic, varies in thickness according to 

 the amount of protection required by the part covered, and, when handled, 

 should feel " loose " and freely movable over the structures beneath. 

 Over the sides of the body it is capable of considerable muscular movement 

 which enables the animal to twitch it violently for the removal of flies. 

 In health the coat should lie flat, feel quite smooth and carry a nice gloss ; 

 want of condition, exposure, privation, neglect, or ill-health may cause it 

 to " stare," that is, stand on end ; look " dull," or feel " harsh '' ; and under 

 similar circumstances the whole skin may lose its usual mobility, and feel 

 as if glued^to the ribs, a condition known as "hidebound." 



The rouHne of the body. — Having taken a survey of the body com- xhe 

 ponents and their functions, we can now assemble the whole and vie\vthe routine of 

 result of their working as one machine. The routine work of the body is the body, 

 comparable to that of an engine which by the combustion of coal (food) 

 produces heat (work) and ashes (waste). 



The complex substances eaten as food are broken up by the digestion 

 into simpler materials which can be absorbed by the intestines, and this 

 nourishment finds its way, via the liver and lymphatics, into the blood. 

 By this channel it is carried to the capillary circulation of every organ ; 

 here it slips into the muscles and is converted into " energy," " work." 

 Both these operations, viz., the conversion of food into nourishment, and 

 the using of this to do work, are productive of heat. The heat produced 

 is regulated so that it remains practically constant (the temperature), 

 and in this regulation, the skin (sweating) and the lungs (breathing), 

 assisted by the bowels and kidneys, take the leading parts. With such 

 changes constantly occurring, there must of necessity be considerable 

 (b 10948) B 



