396 FOUNDATIONS OF BIOLOGY 



its part to play in putting the various constituents of the food 

 into such a form that they can pass to the various cells of 

 the body where they are actually used. 



On the side of respiration, a closer approach was made 

 toward a true understanding of the process. In France 

 LAVOISIER (1743-1794) made it clear that the chemical 

 changes taking place in respiration involve essentially a 

 process of combustion, and it only remained for later work 

 to show that this takes place in the tissues rather than in 

 the lungs. 



Enough perhaps has been said to indicate the trend of 

 physiology away from the maze of Galenic "spirits" in 

 which science lost itself, toward the modern viewpoint of 

 science which assumes as its working hypothesis that life phe- 

 nomena are an expression of a complex interaction of physico- 

 chemical laws which do not differ fundamentally from the 

 so-called laws operating in the inorganic world, and that the 

 economy of the organism is in accord with the law of the 

 conservation of energy probably the most far-reaching 

 generalization attained by science during the past century. 



Most of the firm foundation on which the physiology of 

 animals rests to-day has been built up by the work on Verte- 

 brates. But since the middle of the nineteenth century, 

 when the versatile MULLER (1801-1858) of Germany empha- 

 sized the value of studying the physiology of higher and lower 

 animals alike, there has been an ever-increasing tendency 

 to focus evidence, in so far as possible, from all forms of life 

 on general problems of function. This has culminated in the 

 science of COMPARATIVE PHYSIOLOGY. 



The less obvious structural and functional differentiation 

 of plants retarded progress in plant physiology as it did in 

 plant anatomy. Probably of most historical and certainly 

 of most general interest is the development of our knowledge 



