LIVING SUBSTANCE 131 



have a chaiTed appearance, and, when brought into water, dis- 

 integrate into a clayey pulp. Nevertheless, from several observa- 

 tions it appears certain that many plant-seeds, when completely 

 dried, can retain their power of sprouting for more than a hundred, 

 perhaps for more than two hundred, years. 



These rare facts are of great importance in forming a conception 

 of life, and demand exhaustive investigation. The question to be 

 considered is whether it is allowable to regard organisms in this 

 peculiar condition as really lifeless. 



Theoretically, in its most general expression, the distinction 

 between living and lifeless organisms meets with no great diffi- 

 culties. Our conception of life has been formed from the observa- 

 tion of certain phenomena which appear only in living organisms, 

 in other words, vital phenomena. Wherever we observe vital 

 phenomena we speak of a living organism. This characterisation 

 of the conception of life can be simplified still more. If, for 

 example, all the varieties of vital phenomena be recalled, it is 

 found that they arrange themselves into three great groups, — 

 those of metabolism, or change of substance, those of change of 

 form, and those of transformation of energy. Every living 

 organism exhibits changes in its comjjonent materials, since it 

 continually takes in substances from the outside and gives off 

 others to the outside ; it exhibits changes of its form, since it 

 develops, grows, and reproduces by constricting off certain parts ; 

 and it exhibits changes of its energy, since it transforms the chem- 

 ical energy received with its food into other forms of energy. 

 But these changes are not three whollj' different processes, which 

 are independent of one another ; they are, rather, different kinds of 

 phenomena of one and the same process. No substance exists 

 without form or energy. Substance, form, and energy are simply 

 the three phases in which the physical world can manifest itself 

 in phenomena, in which matter can be considered. Every change 

 of substance necessitates a simultaneous change in the two 

 other phases, although in a given case one phase is more evident 

 to the senses than another. Hence it can be said that in a 

 general sense the vital process, the outward expression of which 

 is perceived in the various vital phenomena, consists in changes 

 of substance, or, in brief, metabolism. Accordingly, it is meta- 

 bolism in which the living organism differs from the lifeless. 



Practically, i.e., in a concrete case, this distinction is not always 

 so simple, as is evident from the case of desiccated organisms. In 

 accordance with the above considerations, it is a question whether 

 these organisms in their peculiar condition possess really no meta- 

 bolism, or whether their metabolism is simply depressed to go 

 slight a degree that it is not apparent to our unaided senses in 

 the form of vital phenomena, i.e., whether the life-process is at an 

 actual standstill, or whether only a vita minima exists. The 

 decision of this question is possible only by means of the most 



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