CHEMICAL RELATIONS OF PROTOPLASM. 33 



tegrates, and wastes away, giving off as waste matter the various 

 chemical products of the combustion, and liberating energy as 

 heat and mechanical work. The loss of substance is, however, 

 continually made good (much as the coal is replenished) by the 

 absorption of new substance in the form of food, which may 

 consist of actual protoplasm, derived from other living beings, 

 or of substances convertible into it. These substances are in 

 some unexplained way converted into protoplasm and thus 

 built into the living fabric. 



To this dual process of waste ( li fcatafiolism") and repair 

 ("anabolism") is applied the term metabolism, which must be 

 considered as the most characteristic and fundamental property 

 of living matter. It is evident from the foregoing that meta- 

 bolism involves on the one hand a destructive action (katabol- 

 ism) through which protoplasm disintegrates and energv is set 

 free, and on the other hand a constructive action (anabolisni) 

 whereby new protoplasm is built up from the income of food and 

 fresh energy is stored. It is a most remarkable fact that as far 

 as known the constructive action resulting in the formation of 

 new protoplasm never takes place except through the immediate 

 agency of protoplasm already existing. In other words, there is 

 no evidence that k " spontaneous generation" or the production 

 of living from lifeless matter without the influence of antecedent 

 life ever takes place.' Xor is there any evidence that any energy 

 can be ' ' generated, ' ' but rather that the vital energy of living 

 things is only the transformed energy of their food, and that 

 "vital force" having an origin elsewhere than in such energy 

 does not exist. 



Chemical Relations. We know nothing of the precise chemi- 

 cal composition of living protoplasm, because, as has been said 

 (p. 2), living protoplasm cannot be subjected to chemical analy- 

 sis without destroying its life. But the results of chemical ex- 

 aminations leave no doubt that the molecules of protoplasm are 

 highly complex and are probably separated 'from one another by 

 layers of water. 



A. PROTEIDS. It has already been stated (p. 3) that the 

 characteristic products of the analysis of protoplasm are the 

 group of closely-related substances known &sproteids. But pro- 

 teids form only a small part of the total weight of any plant or 



