THE 



METAMORPHOSIS OF TISSUES. 



1, THE absolute identity of composition in the 

 chief constituents of blood and the nitrogenised 

 compounds in vegetable food would, some years ago, 

 have furnished a plausible reason for denying the 

 accuracy of the chemical analyses leading to such a 

 result. At that period, experiment had not as yet 

 demonstrated the existence of numerous compounds, 

 both containing nitrogen and devoid of that element, 

 which, with the greatest diversity in external charac- 

 ters, yet possess the very same composition in 100 

 parts ; nay, many of which even contain the same 

 absolute amount of equivalents of each element. 

 Such examples are now very frequent, and are 

 known by the names of isomeric and polymeric 

 compounds. 



2. Cyanuric acid, for example, is a nitrogenised 

 compound which crystallizes in beautiful transparent 

 octahedrons, easily soluble in water and in acids, 

 and very permanent. Cyamelide is a second body r 

 absolutely insoluble in water and acids, white 

 and opaque like porcelain or magnesia. Hydrated 

 cyanic acid is a third compound, which is a liquid, 

 more volatile than pure acetic acid, which blisters 



