2 THE SIMPLER NATURAL BASES 



general biological importance. Thus the basic nature of morphine was 

 recognised as long ago as 1806, and in 1820 quite half a dozen of the 

 most important vegetable alkaloids were known, but our knowledge of 

 animal bases is of a much later date. Pettenkofer prepared creatinine 

 from urine in 1844 and Strecker first obtained choline from pig's bile 

 in 1849, but for a long time hardly any other animal bases were known, 

 and betaine, which is now known to occur in many plants and some 

 animals, was not discovered until 1863. The more volatile amines, 

 trimethylamine and amylamine, were obtained as putrefaction pro- 

 ducts in 1855 and 1857 respectively, and about the year 1866 it 

 became generally recognised that bases are formed in putrefaction, but 

 for a long time these bases were regarded as similar to the vegetable 

 alkaloids, and their isolation was attempted by similar methods. For 

 this there were two reasons. In the first place the poisonous properties 

 of putrid material were considered analogous to those of plant alkaloids, 

 and secondly the medico-legal examination of corpses in murder trials 

 revealed the presence of bases (called ptomaines by Selmi) which gave 

 reactions like those of coniine, nicotine, atropine, etc. In no single 

 instance did these early investigations result in the preparation of a 

 pure substance, so that they do not concern us further. 



The chemistry of putrefaction bases may be said to begin in 1876 

 when Nencki correctly analysed a base C 8 H n N, obtained from putrid 

 gelatin ; he afterwards identified it as phenylethylamine. It seems 

 highly probable that this amine, perhaps mixed with diamines, was 

 the " animal coniine " of earlier investigators. 



The next great advance was due to Brieger who, breaking away 

 from the methods used for plant alkaloids, and relying chiefly on 

 mercuric chloride, platinic chloride and similar reagents, discovered 

 putrescine, cadaverine, and many putrefaction bases which had been 

 overlooked by his predecessors. Gradually it became evident that pto- 

 maines, or putrefaction bases, are the products of bacterial action on 

 protein and phosphatides, and since then our knowledge of these bases 

 has become more and more intimately associated with what we know 

 of the amino-acids from which protein is built up. Two examples of 

 this association may be given. The discovery of phenylalanine by 

 Schulze and Barbieri in 1881 enabled Nencki to surmise the constitu- 

 tion of his base C 8 H n N referred to above ; it is derived from the amino- 

 acid by loss of carbon dioxide. Later Ellinger proved that Brieger's 

 diamines were similarly derived from the amino-acids ornithine and 

 lysine. 



Since then the amines corresponding to nearly all the known 



