SCIENCE OF COMMON THINGS. 237 



Why no heat In the hair. Two kinds of blood, venous and arterial. 



ning all over the body ; they are called capillary from 

 the Latin word capillaris, " like a hair." 



1537* Do these capillary vessels run all over the human body f 



Yes. Whenever Hood flows from a wound, some 

 vein or vessel must be divided ; and as you can bring 

 blood from any part of the body by a very slight 

 wound, these little vessels must run through every part 

 of the human frame. 



1588 How do hydrogen gas and carbon get into these very small 

 vessels ? 



The food we eat is converted into blood, and blood 

 contains both hydrogen and carbon. 



1580 Does this combustion, and the consequent production of animal 

 heat, take place in every part of the body ? 



In the animal body, heat is produced only in those 

 parts to which arterial Hood, and with it the oxygen 

 absorbed in respiration, is conveyed. 



1590 Why is there no heat developed in hair, wool, andfeaffiers f 



Because they receive no arterial Hood, and therefore 

 in them no heat is developed. 



1591 What two kinds of blood are tliere in the animal body ? 



Arterial Hood and venous Hood. 



159 S What is the difference between the two? 



The arterial blood going from the lungs conveys the 

 oxygen which it has absorbed in the lungs to the capil- 

 lary vessels. In these the combustion takes place, and 

 the color of the blood changes from a bright to a dark 

 red color. 



1593 What becomes of the blood after it has given up its oxygen to the 

 hydrogen and carbon in the capillary vessels f 



It enters the veins, carrying with it the products of 

 combustion. The venous blood passes to the lungs, 

 throws off the products of combustion, absorbs more 

 oxygen, becomes converted into arterial blood, with 

 a renewal of color, and is again returned into the 

 system. 



1594 What becomes of the carbonic acid gas formed in the human 

 blood ? 



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