INTRODUCTION AND SCOPE 3 



amino-acids have been found to occur as putrefaction products. These 

 amines are described in Chapter I and include substances with inter- 

 esting physiological actions. Another group of bases, likewise derived 

 from protein, is described in Chapter II. The members of this group 

 still retain a carboxyl group of the amino-acid, so that they are but 

 feebly basic, and without marked physiological action. They include 

 the w-amino-acids, formed by putrefaction, and urocanic and kynurenic 

 acids, two substances occurring in dog's urine and derived from 

 histidine and tryptophane respectively. A third group of simple bases 

 related to the amino-acids of protein is dealt with in Chapter III, 

 namely that of the betaines, derived from amino-acids by methylation. 

 Several new examples of this class have been discovered during the 

 last few years, both in animals and in plants. 



The first three chapters deal therefore with bases which are de- 

 rived by slight modifications from the constituent units of protein. 

 These modifications are irreversible. As long as protein is not 

 broken down beyond the amino-acid stage, its fragments are still 

 available for synthesis. Thus when an amino-acid is set free in the 

 germinating seed by the action of proteoclastic enzymes, it may 

 re-enter a protein molecule in a cell of the growing point. If the de- 

 gradation of protein proceeds farther, if the amino-acid is de-aminized 

 or decarboxylated and also probably if it is methylated, it is no 

 longer available for protein synthesis in animals and in the higher 

 plants ; it no longer constitutes a food, except for bacteria and some 

 fungi. To these degradation products of protein which have passed 

 out of the metabolic circulation, Ackermann and Kutscher [1910, 2] 

 have applied the term aporrhegmata. They include under this denomina- 

 tion not only bases, but alst> acidic products, such as succinic acid, 

 which is derived from aspartic acid by the loss of an amino-group 

 during putrefaction. 



In addition to the proteins, lecithin and other phosphatides con- 

 stitute a source of bases in the organism. Here there is less variety, 

 for only two primary fission products of basic character are known with 

 certainty, choline and amino-ethyl alcohol. Neurine and trimethyl- 

 amine are secondary decomposition products of choline and there are 

 also a few closely related bases, like muscarine. All these bases are 

 described in Chapter IV (with the exception of trimethylamine, which 

 is included in Chapter I as it may also be formed from sources other 

 than choline). 



Of the bases dealt with in the first four chapters some are found in 

 animals, some in plants, and many in both ; the remaining chapters 



I * 



