PREFACE. 



BY the application to chemistry of the methods which had for centuries been 

 followed by philosophers in ascertaining the causes of natural phenomena in 

 physics by the observation of weight and measure LAVOISIER laid the founda- 

 tion of a new science, which, having been cultivated by a host of distinguished 

 men, has, in a singularly short period, reached a high degree of perfection. 



It was the investigation and determination of all the conditions which are essen- 

 tial to an observation or an experiment, and the discovery of the true principles of 

 scientific research, that protected chemists from error, and conducted them, by a 

 way equally simple and secure, to discoveries which have shed a brilliant light on 

 those natural phenomena which were previously the most obscure and incompre- 

 hensible. 



The most useful applications to the arts, to industry, and to all branches of 

 knowledge related to chemistry, sprung from the laws thus established ; and this 

 influence was not delayed till chemistry had attained its highest perfection, but 

 came into action with each new observation. 



All existing experience and observation in other departments of science reacted, 

 in like manner, on the improvement and development of chemistry; so that 

 chemistry received from metallurgy and from other industrial arts as much benefit 

 as she had conferred on them. While they simultaneously increased in wealth, 

 they mutually contributed to the development of each other. 



After mineral chemistry had gradually attained its present state of development, 

 the labours of chemists took a new direction. From the study of the constituent 

 parts of vegetables and animals, new and altered views have arisen; and the 

 present work is an attempt to apply these views to physiology and pathology. 



In earlier times the attempt has been made, and often with great success, to 

 apply to the objects of the medical art the views derived from an acquaintance with 

 chemical observations. Indeed, the great physicians, who lived towards the end 

 of the seventeenth century, were the founders of chemistry, and in those days the 

 only philosophers acquainted with it. The phlogistic system was the dawn of a 

 new day ; it was the victory of philosophy over the rudest empiricism. 



With all its discoveries, modern chemistry has performed but slender services to 

 physiology and pathology ; and we cannot be deceived as to the cause of this 

 failure, if we reflect that it was found impossible to trace any sort of relation be- 

 tween the observations made in inorganic chemistry, the knowledge of the charac- 

 ters of the elementary bodies and of such of their compounds as could be formed 

 in the laboratory, on the one hand, and the living body, with the characters of its 

 constituents, on the other. 



Physiology took no share in the advancement of chemistry, because for a long 

 period she received from the latter science no assistance in her own development. 

 This state of matters has been entirely changed within five and twenty years. But 

 during this period physiology has also acquired new ways and methods of investi- 

 gation within her own province ; and it is only the exhaustion of these sources oi 



A2 5 



