16 METHODOLOGICAL INTRODUCTION. 



gradual metamorphosis, and its transition through different stages 

 of oxidation, and into bodies containing a larger quantity of oxygen. 

 He believed that he could most readily attain this object by the 

 comparative analytical method ; and hence he and his school 

 entered upon a series of experiments on the numerous products of 

 decomposition of fatty matters, and more especially on their pro- 

 ducts of oxidation ; and although we may still be far removed 

 from the object in view, these enquiries have enriched us with 

 many valuable results. A similar instance is afforded by the 

 gelatigenous tissues of the animal body; for although our histo- 

 logical and statistico-chemical investigations leave not the slightest 

 doubt that the gelatin is formed from the albuminous matters, the 

 process of this metamorphosis is still wholly unexplained ; and 

 before we shall be justified in forming an opinion regarding this 

 metamorphosis, and expressing it by a chemical equation, it is 

 indispensably necessary that we should investigate the metamor- 

 phoses experienced by albuminous bodies during their gradual 

 oxidation. We are indebted for these views to the admirable in- 

 vestigations prosecuted under Liebig's direction, by Schlieper 

 and Guckelberger, on the products of oxidation of albuminous 

 bodies and of gelatin. 



As we learn more thoroughly to investigate the processes of 

 putrefaction and decomposition, and that of the dry distillation of 

 individual animal substances, and therefore the better to understand 

 their regressive metamorphoses, we may hope by this know- 

 ledge to arrive at a deduction, based on some probability, re- 

 garding their progressive metamorphoses. Among these probable 

 deductions we may place Dessaigne's discovery of the decomposi- 

 tion of hippuric acid into glycine and benzoic acid, Liebig's in- 

 vestigation of creatin, and his pupils' analyses of glycine (glyco- 

 coll), which although they do not yet afford us any perfect eluci- 

 dation of the metamorphoses of animal matter, nevertheless yield 

 many sure points of support for future enquiries on the vital pro- 

 cesses. 



A third method, which although frequently employed, has 

 hitherto, from the imperfect state of our knowledge, yielded few re- 

 liable results, is the physiologico-exper intent aL By this term 

 we would designate that class of enquiries, in which obser- 

 vations are made in the living organism on the result of cer- 

 tain conditions on the progress of a physiologico-chemical pro- 

 cess, and on the different stages of that process. We are aware 

 that we shall never succeed in artificially reproducing all the 



