ii4 The Science of Life. 



becomes molecularly more complex and more unstable. 

 On the other hand, the continually recuperated proto- 

 plasm becomes active as a source of energy, and breaks 

 down in a descending 1 series of disruptive chemical 

 changes ending in waste products. 



Since physiology attained to precision of statement it 

 has been recognized that there is in life a twofold pro- 

 Anaboiism cess ^ wag te and repair, of activity and 

 and Kata- recuperation, of disruption and construction. 

 One of the first to make this general idea 

 more precise was De Blainville, who described vitality 

 "as a twofold internal movement of composition and 

 decomposition". At a later date, Claude Bernard, who 

 may be called the pioneer of the " protoplasmic move- 

 ment", distinguished " disassimilating combustion and 

 assimilating synthesis". Of recent years various re- 

 searches and speculations, especially those of Hering 

 and of Gaskell, have led to yet more precise statements 

 in regard to metabolism, perhaps more precise than the 

 known facts warrant. 



Generalizing from his studies on colour sensation, 

 Hering was led to regard all life as an alternation of 

 two kinds of activity, the one tending to storage, con- 

 struction, or assimilation of material, the other tending 

 to explosion, disruption, or dissimilation. 



" Metabolism", he says, " is, physiologically speaking, 

 the essential distinction between living and dead matter. 

 It signifies the chemical processes in living substance, 

 by which, on the one hand, certain products are excreted 

 as foreign bodies, and either accumulate in situ, or pass 

 out into the circulating fluids ; while, on the other, there 

 is a simultaneous intake of nutritive matters to form 

 new constituents. This last function is known as assi- 

 milation; the first may be termed dissimilation." 



" In distinguishing these functions, we must not fall 

 into the error of regarding them as two intrinsically 

 separate, parallel processes, and the living matter itself 

 as a quiescent mass, used up on one side and replaced 

 on the other. . . . Assimilation and dissimilation 

 must rather be conceived as two closely interwoven 

 processes, which constitute the metabolism (unknown 



