EFFICIENT RESPIRATION. 177 



Is a condition incompatible with a quick supply of 

 blood, or a high degree of respiration ; for if these 

 were conjoined, they would only give rise to an 

 amount of bodily activity at variance with the ab- 

 sorbed and inactive state of the mind. The nature 

 of the exciting passions, again, is to impel us vigor- 

 ously to action ; but action cannot be sustained with- 

 out a full supply of highly oxygenated blood, and hence 

 a very manifest reason for the quick respiration and 

 accelerated circulation which attend mental excite- 

 ment. Great depression of mind thus leads naturally 

 to imperfect respiration, a more sluggish flow of 

 blood, and the various diseases of diminished vi- 

 tality ; while great excitement induces full respira- 

 tion, quickened circulation, and the various diseases 

 of exalted vitality. These principles show the para- 

 mount importance, in the treatment of disease, of 

 carefully regulating the mental state of the patient, 

 according to the object we have in view. 



A fourth essential condition of healthy respira- 

 tion remains to be noticed, viz. a regular supply of 

 vure fresh air, without which the requisite changes 

 in the constitution of the blood, as it passes through 

 the lungs, cannot be effected. To enable the reader 

 to appreciate this condition, we must premise some 

 remarks on the nature of the changes alluded to. 



Atmospheric air consists of nearly 79 per cent. 

 of nitrogen or azotic gas, 21 per cent, of oxygen, 

 and not quite 1 per cent, of carbonic acid or fixed 

 air : and such is its constitution when taken into 

 the lungs in the act of breathing. When it is ex- 

 pelled from them, however, its composition is found 

 to be greatly altered. The quantity of nitrogen re- 

 mains nearly the same, but 8 or 8 per cent, of the 

 oxygen or vital air has disappeared, and been re- 

 placed by an equal amount of carbonic acid. In addi- 

 tion to these changes, the expired air is loaded with 

 moisture. Simultaneously with these occurrences, 

 the blood collected from the veins, which entere4 



