IN POPULAR CHEMISTRY. 63 



There is an absence of oxygen, so essential to every vital 

 operation, and also an accumulation of carbonic acid in the 

 system. 



0. Wiiy do we breathe so slowly when ive sleep ? 



The circulation is less rapid, and various functions of the 

 body are less active. There is hence less need for rapid oxi- 

 dation. 



10. Hoiv does a cold-blooded animal differ from a 

 warm-blooded one ? 



In the imperfection with which the blood is oxygenated. 

 The lungs are often of small capacity, and loose texture, and 

 are sometimes wanting entirely. In reptiles a portion of the 

 blood is not sent to the heart, and hence in the vessels there is 

 a mixture of arterial and venous blood. The breathing is there- 

 fore slow, the motions are languid, and there is little heat. 



11. Why does not the body burn otit like a candle ? 



Because it is renewed by the processes of assimilation and 

 nutrition as rapidly as it is destroyed by the waste of oxida- 

 tion. Whenever the former are in excess we gain flesh ; when 

 the latter, we grow poor. 



12. Do all parts of the body change alike? 



The rate of change varies with the amount of oxidation, 

 and that depends on the use of the organ. The right arm of 

 the blacksmith must be transformed much more rapidly than 

 the left. 



13. WJiat objects would escape combustion if the air 

 were undiluted O ? 



Burnt bodies, i.e., those which are already combined with 

 oxygen. 



14. Why is it difficult to obtain O from the air ? 



Because, although free from combination, it is intimately 

 mixed with N. 



15. What ^veight of O can be obtained from 1O (/rams 

 ofHgO? 



