282 INDUCTION. 



the cause which sustains the temperature of the body. But into this 

 portion' of the speculation we need not enter.* 



This example displays the second mode of resolving complex laws, 

 by tlie interpolation of intermediate links in the chain of causation ; 

 and some of the steps of the deduction exhibit cases of the first mode, 

 that which mfers the joint effect of two or more causes from their 

 separate effects ; but to trace out in detail these exemplifications may 

 be left to the intelligence of the reader. The third mode is not em- 

 ployed in this example, since the simpler laws into which those of 

 respiration are resolved (the laws of the chemical action of the oxides 

 of iron) were already known laws, and did not acquire any additional 

 generality fi'om their employment in the present case. 



§ 3. The property which salt possesses of presei'\'ing animal sub* 

 stances from putrefaction is resolved by Liebig into two more general 

 laws, the strong attraction of salt for water, and the necessity of the 

 presence of "water as a condition of putrefaction. The intermediate 

 phenomenon which is intei-polated between the remote cause and the 

 effect, can here be not merely inferred but seen ; for it is a familiar 

 fact, that flesh upon which salt has been thrown is speedily found 

 swimming in brine. 



The second of the two factors (as they may be termed) into which 

 the preceding law has been resolved, the necessity of water to putre- 

 faction, itself affords an additional example of the Resolution of Laws. 

 The law itself is proved by the Method of Difference, since flesh com- 

 pletely dried and kept in a dry atmosphere does not putrefy, as we 

 see . in the case of dried pro%-isions, and human bodies in very dry 

 climates. A deductive explanation of this same law results fi"om 

 Liebig's speculations. The putrefaction of animal and other azotiz;ed 

 bodies is a chemical process, by which they are gi'adually dissipated in 

 a gaseous form, chiefly in that of carbonic acid and ammonia ; now to 

 convert the carbon of the animal substance into carbonic acid requires 

 oxygen, and to convert the azote into ammonia requires hydrogen, 

 which are the elements of water. The extreme rapidity of the putre- 

 faction of azotized substances, compai'ed with the gradual decay of 

 non-azotized bodies (such as wood and the like) by the action of 

 oxygen alone, is explained -by Liebig from the general law that 

 •substances are much more easily decomposed by the action of two 

 different affinities upon two of their elements, than by the action of 

 only one. 



The purgative effect of salt with alkaline bases, when administered 

 in concentrated solutioris, is explained by Liebig from the two follow- 

 ing principles : Animal tissues (such as the stomach) do not absorb 

 concentrated solutions of alkaline salts ; and such solutions do dissolve 

 the solids contained in the intestines. The simpler, laws into which 

 the complex law is here resolved, are the second of the two foregoing 



* As corroborating the opinion of Liebig that the protoxide of iron in the venous blood 

 is only partially carbonated, the fact has been suggested that the system shows, graet readi- 

 ness to absorb an extra quantity of carbonic acid, as furnished in etrervescing drinks. In 

 snch cases the acid must combine with something, and that something is probably the free 

 protoxide. It would be worth asc^taining whether the protoxide itself or its carbonate 

 Jias the greater facility in absorbing oxygen and turning itself into hydrated peroxide in 

 the lungs. If the carbonate, Ihen the beneficial effect, on the animal economy, of drinks 

 which give an artificial supply of carbonic acid to the system, would be, to that extent 

 deductively demonstrated. 



