OF INVESTIGATION. 541 



phere by respiration ; what the blood receives 

 and what it loses, while passing through the 

 lungs, and during its circulation through the sys- 

 temic capillaries ; above all, what enables it to 

 excite the heart, and maintain the activity of all 

 the vital functions. This should be the ultimate 

 aim of our researches. For if all diseases are 

 owing to some deviation from the natural state of 

 organized bodies, it is clearly impossible to com- 

 prehend the right method of their treatment, 

 without knowing the conditions of healthy action. 



Let us then agree with Aristotle, that, " if 

 there be any description of knowledge more high 

 and excellent than another, it is that of the ani- 

 mating principle." But if the cause of animal 

 life be obtained from the atmosphere by breath- 

 ing, as taught by Moses, and sanctioned by the 

 universal common sense of mankind, it must be a 

 bonafide constituent of the atmosphere, therefore 

 a portion of nature, and not a hyperphysical 

 essence, as supposed by some modern theorists ; 

 who have confounded the physical cause of 

 animal motion with sensation, volition, and 

 thought, which are operations of the nervous 

 system, and not material entities ; for they cannot 

 be added to, and subtracted from bodies, like 

 caloric, electricity, and other forms of matter. 



It also follows, that if the atmosphere be com- 

 posed of oxygen, nitrogen, aqueous vapour, and 

 carbonic acid, united with some still more refined 



