THE 



METAMORPHOSIS OF TISSUES. 



1. THE absolute identity of composition in the chief 

 constituents of blood and the nitrogenized 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 ni- 

 trogen and devoid of that element, which, with the 

 greatest diversity in external characters, yet possess the 

 very same composition in 100 parts ; nay, many of 

 which even contain the same absolute amount of equiv- 

 alents 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 nitrogenized 

 compound, which crystallizes in beautiful transparent 

 octahedrons, easily soluble in water and in acids, and 

 very permanent. Cyamelide is a second body, abso- 

 lutely 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 the skin, and cannot be 



