PROTEINS OK ALBUMINOUS SUBSTANCES 431 



This array of symbols, formidable as it appears, is evidently 

 only that of an amino-acid of which the amino group is at one 

 end of a long chain, while the carboxyl group is at the other. 



Adopting the usual hypothesis as to the configuration of the 

 carbon, and probably the nitrogen atom, the formula in space 

 would be represented by a spiral. 



The early days of organic chemistry were associated almost 

 exclusively with the study of medicine and biology. This was 

 natural owing to the readiness with which definite crystalline 

 principles were obtainable by easy processes from plants and 

 from animal matters. Nearly all the operations undertaken 

 down to the beginning of last century had some practical utili- 

 tarian object, such as the production of dyes or tanning materials, 

 the processes of fermentation, the distillation of spirits, the 

 examination and preparation of drugs. It was only in the hands 

 of a few of the older chemists that organic matters were examined 

 with the primary object of ascertaining something as to their 

 nature. When, however, such a man as the Swedish Scheele 

 (1742-1786) entered the field discoveries were made so rapidly 

 that it appears almost surprising that his example was not 

 followed more freely by others. There were, however, two great 

 difficulties in the way, the one was the lack of methods by 

 which the composition of such compounds could be accurately 

 determined, the other was the absence of the fundamental ideas 

 which would enable the results of such analysis to be interpreted. 

 The latter was provided in due time by the application of Dalton's 

 Atomic Theory (1808), but it was much later before the methods 

 of organic analysis were devised and perfected by Liebig. 



But even before the advent of the Atomic Theory many 

 definite substances had been extracted from natural sources. 

 Citric, tartaric, malic, lactic acids were known, urea and uric 

 acid, asparagine, morphine from opium, and glycerine by 

 saponification of fats, beside hydrocyanic acid and many other 

 carbon compounds. These, however, were isolated examples of 

 naturally occurring principles, and their relations to one another 

 or to the animal or vegetable sources from which they were 

 extracted or to any system of things had yet to be discovered. 

 One of the first important steps was taken when in 1828, Wohler 

 found that the inorganic salt ammonium cyanate by mere 

 evaporation of its aqueous solution was transformed into urea 

 by a rearrangement of its elements without loss or gain of any 



