DEVELOPMENT OF BIOLOGY 463 



In 1779, Priestley (1733-1804) of England, the discoverer of 

 oxygen, showed that this gas under certain conditions is liberated 

 by plants. This fact was seized upon by a native of Holland, 

 Ingenhousz (1730-1799), who demonstrated that carbon dioxide 

 from the air is reduced to its component elements in the leaf during 

 exposure to sunlight. The plant retains the carbon and returns 

 the oxygen — this process of carbon-getting being quite distinct 

 from that of respiration in which carbon dioxide is eliminated. It 

 remained then for de Saussure (1767-1845) in Geneva to show 

 that, in addition to the fixation of carbon, the elements of water 

 are also employed, while from the soil various salts, including com- 

 binations of nitrogen, are obtained. But it was nearly the middle 

 of the last century before the influence and work of Lierig (1803- 

 1873) at Giessen led to a clear realization of the fundamental part 

 played by the chlorophyll of the green leaf in making certain chem- 

 ical elements available to animals. The establishment of the cos- 

 mical function of green plants — the link they supply in the cir- 

 culation of the elements in nature — is an epoch in biological 

 progress. (Figs. 15, 16.) 



Enough perhaps has been said to indicate the trend of physi- 

 ology 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 phenomena 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. 



However, it is important to emphasize that vitalism — the 

 conception that life phenomena are, in part at least, the resultant 

 of manifestations of matter and energy which transcend and differ 

 intrinsically in kind from those displayed in the inorganic world: 

 a denial, as it were, in the organism of the full sufficiency of known 

 fundamental laws of matter and energy — has arisen many times 

 in the development of biological thought. This has been either as a 

 reaction against premature conclusions of the rapidly growing 

 science, or from an overwhelming appreciation of the staggering 

 complexity of life phenomena. (Page 24.) 



Vitalism attained perhaps its most concrete formulation as a 

 doctrine during the early part of the eighteenth century, in opposi- 



