4 METHODOLOGICAL INTRODUCTION. 



tary analysis of its solid residue and of the composition of the 

 individual constituents of the excretions, there is an utter absence of 

 all scientific groundwork ; for, independently of the fact that the 

 elementary analysis of so compound a matter as the blood is 

 incapable of yielding any reliable results, and cannot, therefore, 

 justify the adoption of any special chemical formula, it is assuredly 

 most illogical to attempt to compare the composition of the blood 

 collectively, with that of the separate excrementitious matters. 

 In such deductions, expressed by chemical formulae, the addition 

 of atoms of oxygen, and the subtraction of those of water, carbonic 

 acid, and ammonia are wholly arbitrary: for chemical analyses 

 do not afford the slightest grounds for the majority of these 

 equations. When, on the other hand, we have seen uric acid 

 decomposed by different oxidising agents into urea and other 

 bodies, and when, further, we find the quantity of uric acid in- 

 creased in the urine in those cases where a diminished quantity 

 of oxygen is proved to be contained in the blood, we are justified 

 in concluding that also in the animal organism a portion, at least, 

 of the urea found in the urine must have been produced by the 

 oxidation of the uric acid. In the formula which expresses this 

 deduction, we have an hypothesis, but a well-grounded one, 

 which, although requiring further confirmation, is yet wholly 

 different from the frequently condemned, but rarely avoided, abuse 

 of chemical symbols. Chemical equations having no other 

 foundation than the presumed infallibility of empirical formulae, 

 must, however, cause us to deviate from the path of physical 

 enquiry, and involve us in a chaos of the most untenable delusions. 

 Thus, for instance, a chemical equation might lead us to conclude 

 that glycine (glycocoll) was the source of urea and lactic acid in 

 the metamorphosis of the animal tissues ; for we might con- 

 clude that 2 equivalents of hydrate of glycine were decomposed 

 into the above-named substances according to the formula, 

 C 8 H 10 N 2 O 8 =C 2 H 4 N 2 O 2 + C 6 H 5 O 5 . H O. All experiments 

 hitherto instituted with glycine are, nevertheless, opposed to such 

 a disintegration. If, then, we would deduce urea and lactic acid from 

 glycine, which has not been proved to exist in the blood, we 

 should be neglecting the most comprehensive rule of logic, 

 according to which one hypothesis cannot be supported by 

 another. It has, however, unfortunately been too much the 

 practice in recent times to employ far more complicated equations 

 as supports for such purely subjective modes of contemplation, by 

 which a semblance of the most exact method of investigation has 



