452 MODERN CHEMISTRY. 



originate in vegetable growth. Upon this fact was founded 

 the inference that, by the processes of vegetation, inorganic 

 materials are converted into organic compounds ; which, 

 serving again as food to animal life, create a new class of 

 organic products fulfilling higher purposes in the economy of 

 the world. This view, plausible in itself, has merged in the 

 later discoveries of Liebig, Mulder and others, which prove 

 that not merely the saccharine and oleaginous principles of 

 animals and vegetables are almost identical' in chemical 

 composition, but that even the three great principles of 

 animal tissues albumen, fibrin, and casein have their 

 exact counterparts in certain of the principal products of 

 vegetable life ; the proportions of carbon, oxygen, nitrogen, 

 and hydrogen being precisely the same in each. This dis- 

 covery, startling by its unexpectedness, was followed by 

 attempts at yet larger generalisation, as in Mulder's doctrine 

 of Proleine ; but these have not succeeded in attaining the 

 proof which science requires, -and go no further than to show 

 the difficulty of interpreting the realities of nature by our 

 artificial systems. 



Connected closely with this topic, and better established as 

 a principle, is the important doctrine of Compound Radicals, 

 already mentioned as one of those great general views which 

 especially mark the present a3ra in science. Liebig has even 

 described Organic Chemistry as the c Chemistry of Compound 

 Radicals,' and in this definition there is much of truth. The 

 term expresses a class of compound bodies, possessing a 

 certain unity and stability of composition, through which 

 they fulfill every part of simple bases; uniting as such, 

 not only with elementary bodies, but with each other ; and 

 generating large classes of secondary products, which have 

 all relation to the compound radical thus assumed as a base. 

 Some of the compounds thus characterised have been ob- 

 tained in a separate state as Cyanogen, for example, in 



