2io Human Physiology. 



the blood will be cut off, and the limb will grow weak and cold. 

 But nature has provided against such accidents. Arteries run 

 into each other. The branches above the ligature will enlarge, 

 and in a few days the blood will flow freely in new channels 

 enlarged by the influences of the nervous power, in obedience 

 to the law of demand and supply. We shall see in our next 

 chapter how far the circulation of the blood is from being a 

 mere mechanical operation. It is, on the contrary, everywhere 

 presided over by a masterly skill a wonderful intelligence. 



CHAPTER VI. 



SECRETIONS AND EXCRETIONS. 



Action of the Lungs Ventilation The Liver The Spleen The Kidneys 

 Effects of Animal Food The Intestinal Glands Action of Cathar- 

 tics The Skin Pores Sweat Glands Chill How to Strengthen 

 the Skin. 



IN our view of the blood and its circulation, we have glanced 

 at some of the organs in which certain matters are separated 

 from it, or made out of the materials which it furnishes. Bone, 

 muscle, nerve, cartilage, tendon, membrane, skin, cuticle, hair, 

 nails, scales, feathers, &c., are formed from the blood, and may 

 all, therefore, be termed secretions. Matters cast out of the 

 body as useless or hurtful, are also separated from the blood, 

 for its purification, and these are termed excretions. Life is 

 carried on by these two processes. The body is built up by 

 secretion, and it is purified from its waste, diseased, and dis- 

 easing its really poisonous matters, by excretion. If one stop, 

 the growth or nutrition of the body ceases, and it wastes away, 

 as in consumption; if the other is hindered, the body quickly 



