534 THEORY OF RESPIRATION. 



that of the same parallels west of that great chain, 

 it is because the climate of the Western coast of 

 America is greatly modified and improved by its 

 vicinity to the Pacific ocean. Owing to the 

 unequal distribution of land and sea, mountains, 

 hills, plains, and valleys, there is an endless di- 

 versity of climate, with a corresponding variety 

 of organized beings. 



Theory of Respiration, as connected with 

 Animal temperature. 



NOTHING could afford a more striking proof that 

 " no genuine physiological principle has ever yet 

 been discovered," than the numerous contra- 

 dictory hypotheses now prevailing in regard to 

 the source of animal temperature ; some main- 

 taining with Black, Crawford, Lavoisier, Ellis, 

 and Dalton, that it is evolved in the lungs 

 during respiration, by a chemical process, as in 

 ordinary combustion ; others with Bichat, that 

 " it is a product of all the vital functions." (Life 

 and Death, p. 278.) Within the last twenty 

 years, many have embraced the theory of Sir 

 Benjamin Brodie, who inferred from his own 

 experiments, that animal heat is in some way 

 generated by nervous influence, because me- 

 chanical injuries of the brain and spinal marrow 

 were followed by a reduction of temperature. 



