28 POPULAR SCIENCE MONTHLY. 



it never become integral parts of the machinery. But with the living 

 engine all this is different. The parts of which it is made take up the 

 nutriment or fuel and assimilate it, thus building up new living sub- 

 stance to replace that which is destroyed in the wear and tear associated 

 with activity. This condition of unstable chemical equilibrium is 

 usually designated metabolism, and metabolism is the great and essen- 

 tial attribute of a living as compared with a non-living thing. 



It seems childish at the present day, and before such an audience as 

 this, to point out how essential it is to know the chemical structure as 

 well as the anatomical structure of the component parts of the body. But 

 the early anatomists to whom I have alluded had no conception of the 

 connection of the two sciences. Speaking of Vesalius, Sir Michael 

 Foster says: "The great anatomist would no doubt have made use of 

 his bitterest sarcasms had some one assured him that the fantastic school 

 which was busy with occult secrets and had hopes of turning dross into 

 gold would one day join hands in the investigation of the problems of 

 life with the exact and clear anatomy so dear to him." Nor did 

 Harvey, any more than Vesalius, pay heed to chemical learning. The 

 scientific men of his time ignored and despised the beginning of that 

 chemical knowledge which in later years was to become one of the foun- 

 dations of physiology and the mainstay of the art of medicine. 



The earliest to recognize this important connection was one whose 

 name is usually associated more with charlatanry than with truth, 

 namely, Paracelsus ; and fifty years after the death of that remarkable 

 and curious personality his doctrines were extended and developed by 

 van Helmont. In spite, however, of van Helmont's remarkable insight 

 into the processes of digestion and fermentation, his work was marred 

 by the mysticism of the day which called in the aid of supernatural 

 agencies to explain what could not otherwise be fully comprehended 



In the two hundred and fifty years that have intervened between the 

 death of van Helmont and the present day alchemy became a more and 

 more exact science, and changed its name to chemistry, and a few 

 striking names stand out of men who were able to take the new facts 

 of chemistry and apply them to physiological uses. Of these one may 

 mention Mayow, Lower, Boerhaave, Reaumur, Borelli, Spallanzani, and 

 Lavoisier. Mulder and Holland and Liebig in Germany bring us 

 almost to the present time, and I think they may be said to share the 

 honor of being regarded as the father of modern chemical physiology. 

 This branch of science was first placed on a firm basis by Wohler when 

 he showed that organic compounds can be built out of their elements in 

 the laboratory, and his first successful experiments in connection with 

 the comparatively simple substance urea have been followed by num- 

 berless others, which have made organic chemistry the vast subject it is 

 to-day. 



