AND ANIMAL LIFE. 15 



not occasioned by any condition of the heart or 

 circulation, as is generally supposed, but arises 

 from the diminution of the ordinary and station- 

 ary quantity of air belonging to the chest, and it 

 ceases as soon as the repeated inspirations have 

 re-established the order of nature. 



XXII. I now propose to show in what way 

 " animal heat is not in the direct ratio to the quan- 

 tity of oxygen inhaled, but in the inverse ratio to 

 the quantity of blood exposed to this principle " 



As the blood is not immediately acted upon 

 by the fresh air which is received, it follows that 

 the alterations are to be referred to that already 

 existing in the pulmonary cells ; and, moreover, 

 it is natural to suppose, if we diminish the quan- 

 tity of blood, that the chemical changes will be 

 more complete, because the air will have a less 

 portion to oxygenate. 



In the words of HALLEE, " the effects of ex- 

 piration are, a compressure of the blood-vessels 

 in the lungs, a reduction of the bronchia into 

 more acute angles, a pressure of the reticular 

 small vessels by the weight and contact of the 

 adjacent larger vessels, and an expulsion of the 

 corrupted blood from the lungs, by which means 

 part of the blood hesitating in the capillary ar- 

 teries is urged forward through the veins to the 

 left side of the heart, while, at the same time, 

 that part of the blood is resisted which flows in 

 by the artery from the right ventricle. Expira- 



