PRIESTLEY'S DISCOVERY OF OXYGEN GAS. 387 



You can scarcely form an estimate of the immense consequences 

 that followed this discovery. It was found not alone to aftect chemis- 

 try, properly speaking, it threw a flood of light on every allied science. 

 The chemistry of that day was overthrown. Without any exaggera- 

 tion, I characterize it as the capital discovery of the last age, rivaling 

 in its importance and in its results the great discovery of the preceding 

 century, universal gravitation, by Newton. Extended by the chem- 

 ists of England, France, and Germany, it has utterly exploded meta- 

 physical physiology, which, taking its origin in the dark ages, has 

 been the great barrier to the progress of rational medicine. Whoever 

 will take pains to study with attention the works devoted to the 

 exposition of that ancient system, must be struck with the impenetra- 

 ble obscurity in which it is enveloped. You turn over page after page, 

 and the more you read the more you become confused. It is a con- 

 stant putting of words for things, of phrases for facts. Even in the 

 hands of the most powerful writers, metaphysical physiology is essen- 

 tially unintelligible ; but not so with that other physiology which has 

 arisen in our times, all its statements are clear, precise, distinct ; it re- 

 lies on the exact sciences, such as chemistry and natural philosophy, 

 because it is itself exact. The progress of all the departments of 

 human knowledge is often the same. Two thousand years ago the pa- 

 gans peopled Olympus with many gods ; and so in the infancy of medi- 

 cine the corporeal frame was peopled with many intangible forms — a 

 soul, a mind, a vital power, an instinct, a nervous agent, an aura, and 

 animal spirits without end. But a better knowledge of these things 

 is fast teaching us the eternal truth that, as there is but one God in the 

 heavens, so there is but one spirit in man ; a presiding agent that su- 

 pervises and directs all; that all the acts of life are brought about by 

 the inhalation of atmospheric air ; and that every living animal owes 

 its so-called vital properties to the action of air within its system; 

 that there thus arise oxidations and other alterations in the economy, so 

 that not a movement takes place, nor a thought occurs, without contem- 

 poraneous structural changes. The introduction of air by breathing 

 is, I say, the fundamental fact in physiology ; nay, more, it is the fun- 

 damental event in the action of the brain. I rest my opinions not on 

 scientific facts, though they are numerous and irresistible, but I go at 

 once to an authority far beyond all chemists and metaphysicians. In 

 vain the physiologist asks me to deny the combustive influence of air 

 in the body, and afiects a fictitious fear of the tendencies of such a 

 doctrine. Shall I not believe the positive declaration of him who is 

 the artificer of these beautiful contrivances ? — shall we accuse the 

 Almighty of materialism when he tells us that "he breathed into his 

 nostrils the breath of life, and man became a living soul ? " 



The circumstances that first direct the mind of a philosopher to 

 discoveries destined to exert an influence over the whole human race 

 cannot fail to be full of interest. So it is in the present case. It hap- 



