THE EEASON WHY. 



217 



" Hast thou not known, hast thou not heard, that the everlasting God, the 



Lord, the Creator of the ends of the earth, fainteth not, neither is weary ? 



there is no searching of his understanding." ISAIAH XL. 



illustration of the softness, moisture, and delicate colour of the 

 mucous membrane is afforded by turning up and examining the 

 under surface of the upper eye -lid. 



914. Why do delicate persons look pale and languid ? 



Because, generally from the want of exercise and fresh air, their 

 blood is deficient of the healthy proportion ofred corpuscles. 



915. Why does exercise and fresh air impart to healthy 

 persons a red and fresh appearance ? 



Because the redness of the blood is due to the amount of oxygen 

 which it contains, and air and exercise oxygenise the blood, and 

 diffuse it throughout the system. 



916. How is the Hood propelled through the arteries? 



By the very powerful contraction (and alternate dilation) of the 

 thick muscles of the heart, assisted also by the muscular cords of the 

 blood-vessels themselves, and in many instances by the compression of 

 the muscles in which the arteries lie embedded. 



917. Why are the capillary arteries capable of receiving 

 the great quantity of Hood sent out -through the larger 

 vessels ? 



Because the capillary vessels are so numerous, that though they 

 are infinitely smaller, they are capable of receiving in their minute 

 tubes the whole of the quantity of blood transmitted to them through 

 the larger vessels. 



918. Why, when we sit with our legs crossed, do we set 

 the foot that is raised move at regular intervals ? 



Because the pressure upoo the muscles of the leg retards the 

 progress of the blood until it forces itself through, tlie compressed 

 vessels, and thereby imparts a pulsation which moves the leg and 

 foot. 



919. Why are capillary llood-vessels found in every part 

 of the system ? 



Because it is through ttese small vessels alone that the substances 

 of the body are renewed and changed. Even the larger blood- 

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