TO 



THE BRITISH ASSOCIATION 



... - -~- -?*. 



FOR 



THE ADVANCEMENT OF SCIENCE. 



AT the meeting of the British Association in Glasgow, in 1840, 1 had the honour 

 to present the first part of a report on the then present state of Organic Chemistry, 

 in which I endeavoured to -develope the doctrines of this science in their bearing 

 on Agriculture and Physiology. 



It affords me now much gratification to be able to communicate to the meeting 

 of the Association for the present year the second part of my labours ; in which I 

 have attempted to trace the application of Organic Chemistry to Animal Physiology 

 and Pathology. 



In the present work an extensive series of phenomena have been treated in 

 their chemical relations ; and although it would be presumptuous to consider the 

 |uestions here raised as being definitely resolved, yet those who are familiar with v 

 chemistry will perceive that the only method which can lead to their final resolu- 

 tion, namely, the quantitative method, has been employed. ^ 



The formulae and equations in the second part, therefore, although they are not 

 to be viewed as ascertained truths, and as furnishing a complete, or the only ex- 

 planation of the vital processes there treated of, are yet true in this sense : that 

 being deduced from facts by logical induction, they must stand as long as no new. 

 facts shall be opposed to them. 



When the chemist shows, for example, that the elements of the bile, added to 

 those of the urate of ammonia, correspond exactly to those of blood, he presents 

 to us a fact which is independent of all hypothesis. It remains for the physiolo- 

 gist to determine, by experiment, whether the conclusions drawn by the chemist 

 from such a fact be accurate or erroneous. And whether this question be answered 

 in the affirmative or in the negative, the fact remains, and will some day find its 

 true explanation. 



I have now to perform the agreeable duty of expressing my sense of the services 

 rendered to me in the preparation of the English edition by my friend, Dr. Gregory. 

 The distinguished station he occupies as a chemist ; the regular education which 

 he has received in the various branches of medicine ; and his intimate acquaintance 

 with the German language all these, taken together, are the best securities that 

 the translation is such as to convey the exact sense of the original ; securities, 

 such as are not often united in the same individual. 



It is my intention to follow this second part with a third, the completion of 

 which, however, cannot be looked for before the lapse of two years. This third 

 part will contain an investigation of the food of man and animals, the analysis of 

 all articles of diet, and the study of the changes which the raw food undergoes in 

 its preparation ; as, for example, in fermentation (bread,) baking, roasting, boiling, 

 &,c. Already, it is true, many analyses have been made for the proposed work ; 

 but the number of objects of investigation is exceedingly large, and in order to 

 determine with accuracy the absolute value of seed, or of flour, or of a species of 

 fodder, 8tc., as food, the ultimate analysis alone is not sufficient; there are required 

 comparative investigations, which present very great difficulties. 



DR. JUSTUS LIEBIG. 

 Giessen* 3d June. 1852. 



(3) 



