PREFACE. Xix 



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 mea- 

 sure 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 suf- 

 ficiently 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 ; and this I consider as the most important 

 object to be gained. 



JUSTUS LIEBIG. 

 Gi ESSEN, April, 1842. 



