EXAMPLES OF THE FOUR METHODS. 483 



is known to combine with the acid, and form a com- 

 pound, which, being insoluble, cannot act at all on 

 animal tissues. So, again, sugar is a well-known 

 antidote to poisoning by salts of copper ; and sugar 

 reduces those salts either into metallic copper, or into 

 the red suboxide, neither of which enters into com- 

 bination with animal matter. The disease called 

 painter's colic, so common in manufactories of white 

 lead, is unknown where the workmen are accustomed 

 to take, as a preservative, sulphuric-acid-lemonade (a 

 solution of sugar rendered acid by sulphuric acid). 

 Now diluted sulphuric acid has the property of decom- 

 posing all compounds of lead with organic matter, and 

 (of course) of preventing them from being formed. 



There is another class of instances, of the nature 

 required by the Method of Difference, which seem at 

 first sight to conflict with the theory. Soluble salts 

 of silver, such for instance as the nitrate, have the 

 same stiffening antiseptic effect on decomposing 

 animal substances as corrosive sublimate and the 

 most deadly metallic poisons ; and when applied to 

 the external parts of the body, the nitrate is a power- 

 ful caustic, depriving those parts of all active vitality, 

 and causing them to be thrown off by the neighbour- 

 ing living structures, in the form of an eschar. The 

 nitrate and the other salts of silver ought, then, it 

 would seem, if the theory be correct, to be poisonous ; 

 yet they may be administered internally with perfect 

 impunity. From this apparent exception arises the 

 strongest confirmation which this theory of Liebig 

 has yet received. Nitrate of silver, in spite of its 

 chemical properties, does not poison when introduced 

 into the stomach; but in the stomach, as in all 

 animal liquids, there is common salt ; and in the 

 stomach there is also free muriatic acid. These sub- 



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