68 THE FOUNDATIONS OF SCIENCE 



Paracelsus (c. 1490-1541) and Stahl (1660-1735) 

 carried into modern times the old ideas of a distinct 

 vital principle, in opposition to the equally old theory 

 that the mechanism at work in the inorganic world 

 was sufficient completely to explain the phenomena 

 of life. Till comparatively recent times, the vitalist 

 thought that the characteristic organic compounds 

 could be produced by life alone, and were beyond 

 the resources of chemical laboratories. 



But in 1828 Wohler (1800-1882) succeeded in 

 preparing artificially the typically organic compound 

 urea, and thereby threw doubt on the prevalent 

 vitalistic hypothesis. Other preparations followed, 

 till in 1887 Fischer and Tafel produced sugar from 

 its elements. 



Simultaneously many physical processes have been 

 found operative in living tissues. In particular the 

 phenomena of solution have thrown light on many 

 of the physiological problems of living cells ; osmotic 

 pressure and the motion of electric ions are the means 

 by which many of the operations of living tissues are 

 carried on. 



In this way much new insight has been obtained 

 on the mechanism, both physical and chemical, by 

 means of which the functions of life are maintained. 

 Nevertheless, the gap between the inorganic world 

 and the world of life shows no signs of being bridged. 

 We are still unable to produce the simplest living 

 cell from dead matter. All known organisms are 



