14 METHODOLOGICAL INTRODUCTION. 



satisfactorily investigated question, there are still several directions 

 to be pursued before we can reach the proper object of our enquiries. 

 It is here most essential that we should be well acquainted with the 

 paths to be followed, for in our search after truth we are compelled 

 to call to our aid hypotheses which might easily lead us into the 

 domain of pure fiction. 



As long as zoo-chemistry and the theory of the juices continue 

 to occupy their present subordinate position, the only method by 

 which the foundation necessary to an exact investigation can be 

 obtained, is that which we may term the statistical. Liebig, 

 Boussingault, and Valentin have indeed, with a more correct view 

 of what was required, attempted to compare the final effects of the 

 whole with the material substrata supplied to the organism. We 

 cannot, it is true, arrive at any conclusion regarding the working of 

 the process itself by a mere juxtaposition and quantitative comparison 

 of the ingesta and excreta of the animal organism, any more than 

 we can judge of the causes and course of diseases by the number 

 of fatal cases recorded : but such experiments furnish us with 

 certain general results which serve as guides to further investiga- 

 tions. Some of the most important questions, whose solution was 

 specially necessary, were unanswerable by any other method. 

 Thus, for instance, it was ascertained, by an accurate investigation 

 of the food, and its comparison with the constituents of the excreta 

 and of the nutrient fluids, that in the ordinary food of animals, 

 albuminous substances occur in sufficient quantity to compensate 

 for the nitrogenous matters lost in the process of nutrition and in the 

 metamorphosis of tissue ; while it was thus at the same time shown, 

 that the animal organism does not necessarily possess the property 

 of generating albuminous matter from other substances containing 

 nitrogen. The question whether the animal organism possessed 

 the property of generating fat was answered in a similar manner ; 

 and it is well known that by means of such statistical observations, 

 (comparing the fat contained in the food with that secreted in the 

 cellular tissue and mixed with the excrements) the contest carried 

 on between Liebig on the one side, and Dumas and Boussingault 

 on the other, regarding the formation of fat, was finally decided 

 in favour of the former. 



This statistical method preserves us from setting up unten- 

 able hypotheses, and prosecuting useless experiments. How long 

 were the minds of natural philosophers haunted with the illusion 

 that animal bodies possessed the power of generating mineral 

 elements, as lime, iron, sulphur, &c., from other elements, or even 



