PREFACE. 



As the study of physical and biological phenomena, of 

 the constitution of matter and of its manifestations becomes 

 more extended and more precise, it tends to prove that the 

 perpetual changes noticed in all things, consist in an uninter- 

 rupted series of decompositions and syntheses; and as the 

 transformations of any one substance have a beginning and 

 an end, it can be said that any substance in process of change 

 undergoes an evolution of which the different successive 

 phases are determined by the physical and chemical proper- 

 ties of its constituent elements.' 



Decompositions follow, as a rule, a very uniform path and 

 lead to simple elements which may be considered as definite. 

 Synthesis, on the other hand, is itself subject to evolution; 

 it leads step by step to compounds that are more and more 

 complicated, varied and numerous, and it is impossible to 

 predict any end to these changes. 



The final result of natural synthesis, the most complicated 

 and the most perfect product known to us, is the chemica"! 

 species which we may call "albuminoid micelle." 1 Its 

 characteristic is that it rebuilds itself as it wears out, or, in 

 other words, that it is continuously undergoing partial 

 decomposition and at the same time a reconstruction of the 



1 The word "micelle" is used to define the units of albuminoid matter of 

 every colloid in the same sense that the word "molecule" expresses the 

 unit of chemical compounds. The word "particle" is used by many Ameri- 

 can authors in the same sense. 



