PRELIMINARY DISCOURSE. 



PHYSIOLOGY* is the science of life. The term life is applied to an ag- 

 gregate of phenomena, which manifest themselves in succession, for a 

 limited time, in organized bodies. Combustion is likewise only a combina- 

 tion of phenomena; oxygen unites with the substance which is burning, 

 caloric is disengaged from it; affinity is the cause of these chemical phe- 

 nomena, as attraction is the cause of the phenomena of Astronomy, and 

 in the same manner as the sensibility and contractility of living and or- 

 ganized bodies are the primary causes of all the phenomena which such 

 bodies exhibit phenomena, which in their union and aggregate succes- 

 sion constitute life. 



The false notions which have been entertained on the subject of life, and 

 the vague definitions which have been given of it, are to be accounted for, 

 by considering that physiologists, instead of regarding life as a simplere- 

 sult have mistaken it for the properties of life. These last are causes; 

 the first is merely an effect, more or less complex : and, as the spring of 

 a watch, or rather the elasticity of that spring, determines by the mere 

 action of the wheels, the motion of the hands, and all the phenomena of 

 which the machine is capable; so the vital properties acting by the or- 

 gans produce alithose effects, which in their combination constitute life.t 

 These effects are more or less numerous, according to the number of the 

 organs; they become more rapid too in their succession, and life more ac- 

 tive, with the increase of energy in the vital properties ; precisely as the 

 motions of a watch become more complicated, stronger or quicker, ac- 

 cording to the greater tension of the spring, or the increased number of 

 the wheels. Sensibility and contractility, are to be ranked amorg primary 

 causes, of whose existence and laws we acquire a knowledp^froni obser- 

 vation, but whose essence eludesour investigation^, and^'dl probably re- 

 main for ever beyond its reach. 



I. OF NATURAL BEINGS. 



The vast domain of nature is divided between two classes of beings. 

 Inorganic beings, possessing merely the common properties of matter; 

 organic and living beings, obeyingparticular laws, though subjected to the 

 general laws which regulate the universe. Each of these two grand di- 

 visions is naturally divided into t\no classes; we meet with inorganic bo- 

 dies under the form of elementary substances', simple and not capable of 



* Anatomy is the science of organization, 

 -f See Appendix, Note A. 



* It would be wrong to infer, from our ignorance of the nature of the vital proper- 

 ties, that physiology is'an uncertain Science. Its certainty in that point of view, 5^ equal 

 to that of other parts of natural philosophy. The chemist, who explains all his com- 

 binations by referring them to the principle of affinity, and the astronomer, who finds in 

 attraction the cauee that rules the universe, are absolutely ignorant of the uature of 

 those properties. Authors Note. 



B 





