280 INDUCTION. 



Between the remote cause, the presence of yeast, and the consequent 

 fermentation of the sugar, there has been interpolated a proximate 

 cause, the chemical action between the particles of the yeast and the 

 elements of air and water. The special law is thus resolved into two 

 others, more general than itself: the first, that yeast is decomposed by 

 the presence of air and water; the second, that matter undergoing 

 chemical action has a tendency to produce similar chemical action in 

 other matter in contact with it. But while the investigation thus aptly 

 exhibits the second mode of the resolution of a complex law, it no less 

 happily exemplifies the third ; the subsumption of special laws under 

 a more general law, by gathering them up into ozie more comprehen- 

 sive expression which includes them all. For the curious fact of the 

 contagious nature of chemical action was only raised into a law of all 

 chemical action by these very investigations ; just as the Newtohian 

 attraction was only recognized as a law of all matter when it was 

 found to explain the phenomena of teiTestrial gravity. Previously to 

 Liebig's investigations, the property in question had only been observed 

 in a few special cases of chemical action; but when his deductive 

 reasonings had established that innumerable effects produced upon 

 weak compounds, by substances none of whose known peculiarities 

 would account for their having such a power, might be explained by 

 considering the supposed special property to exist in all those cases, 

 these numerous generalizations on separate substances were brought 

 together into one law of chemical action in general : the peculiarities 

 of the various substances being, in fact, . elimina,ted, just as the New- 

 tonian deduction eliminated from the instances of terrestrial gravity 

 the circumstance of proximity to the earth. 



§ 2. Another of Liebig's speculations, which, if it should ultimately 

 be found to agi'ee with all the facts of the extremely complicated 

 phenomenon to which it relates, will constitute one of the finest, 

 examples of the Deductive Method upon record, is his theory of respi- 

 ration. 



The facts of respiration, or in other words the special laws which 

 Liebig has attempted to explain from, and resolve into, more general 

 ones, are, that the blood in passing through the lungs absorbs oxygen 

 and gives out carbonic acid gas, changing thei'eby its color from a 

 blackish purple to a brilliant red. The absorption and exhalation are 

 evidently chemical phenomena ; and the carbon of the ca,rbonic acid 

 must have been derived fi-om the body, that is, must have been ab- 

 sorbed by the blood from the substances with which it came into 

 contact in its passage through the organism.. Required to find the 

 intermediate links, the precise nature of the two chemical actions which 

 take place ; first, the absorption of the carbon or of the carbonie acid 

 by the blood, in its circulation through the body ; next, the excretion 

 of the carbon, or the exchange of the carbonic acid for oxygen, in its 

 passage through the lungs. 



Dr. Liebig believes himself to have found the solution of tliis vexata 

 qucestio in a class of chemical actions in which scarcely any less acute 

 and accurate inquirer would have thought of looking for it. 



Blood is composed of two parts, the serum and the globules. The 

 serum absorbs and holds in solution carbonic acid in great quantity, 

 but has no tendency either to part with it or to absorb oxygen. The 



