Vlll PREFACE. 



of the body ; and the limited acquaintance of physiologists with the methods of 

 research employed in chemistry will continue to be the chief impediment to the 

 progress of physiology, as well as a reproach which that science cannot escape, 



Before the time of Lavoisier, Scheele, and Priestley, chemistry was not more 

 closely related to physics than she is now to physiology. At the present day 

 chemistry is so fused, as it were, into physics, that it would be a difficult matter 

 to draw the line between them distinctly. The connection between chemistry and 

 physiology is the same, and in another half century it will be found impossible to 

 separate them. 



Our questions and our experiments intersect in numberless curved lines the 

 straight line that leads to truth. It is the p6ints of intersection that indicate to us 

 the true direction ; but, owing to the imperfection of the human intellect, these 

 curve lines must be pursued. Observers in chemistry and physics have the eye 

 ever fixed on the object which they seek to attain. One may succeed, for a space, 

 in following the direct line; but all are prepared for circuitous paths. Never 

 doubting of the ultimate success of their efforts, provided they exhibit constancy 

 and perseverance, their eagerness and courage are only exalied by difficulties. 



Detached observations, without connection, are points scattered over the plain, 

 which do* not allow us to choose a decided path. For centuries chemistry pre- 

 sented nothing but these points, and sufficient means were available to fill up the 

 intervals between them. But permanent discoveries and real progress were only 

 made when chemists ceased to make use of fancy to connect them. 

 / My object in the present work has been to direct attention to the points of inlex- 

 section of chemistry with physiology, and to point out those parts in which the 

 sciences become, as it were, mixed up together. It contains a collection of 

 problems, such as chemistry at present requires to be resolved ; and a number of 

 conclusions drawn according to the rules of that science from such observations 

 as have been made. 



These questions and problems will be resolved : and we cannot doubt that we 

 shall have in that case a new physiology and a rational pathology. Our sounding 

 line, indeed, is not long enough to measure the depths of the sea, but is not on 

 that account less valuable to us : if it assist us, in the mean time, to avoid rocks 

 and shoals, its use is sufficiently obvious. In the hands of the physiologist, organic 

 chemistry must become an intellectual instrument, by means of which he will be 

 enabled to trace the causes of phenomena invisible to the bodily sight ; and if 

 among the results which I have developed or indicated in this work, one alone 

 shall admit of a useful application, I shall consider the object for which it was 

 written as fully attained. The path which has led to it will open up other paths j 

 and this I consider as the most important cbject to be gained. 



JUSTUS LIEB G. 



Giessen, April, 1852. 



