LIVING SUBSTANCE 123 



called living, and, on the other hand, in the resting plant-seed 

 there is seen a condition of the organism in which, while it is 

 not dead, not the slightest movement can be recognised. Thus 

 the significance of movement in its primitive form has now dis- 

 appeared, and in place of it more special motile phenomena have 

 been sought as distinguishing marks between organisms and 

 inorganic bodies. 



It has been thought that a difference must be recognised in the 

 causes that produce movements, on the one hand, of organisms, 

 and, on the other, of inorganic bodies. The former, such as muscle- 

 movements, are said to result from internal causes — those that have 

 their seat in the organism itself; the latter, such as the movement 

 of waves and clouds, from external causes — those that, like the wind, 

 act upon the object from without. The mystical vital force is here 

 more or less evident. But we have already become convinced of 

 the non-existence of such a force, and the claim of such a difference 

 in the causes of movement cannot be maintained. Moreover, in 

 many cases it is difficult to draw a sharp boundary between internal 

 and external causes. E.g., if a steam-engine, and not winds and 

 waves, be considered, it can be said of it, with as much right as 

 of the organism, that it works from internal causes, for the 

 pressure of the steam which drives the piston and puts the 

 wheels in motion is in the interior of the boiler. 



But it has been said that the difference between the causes of 

 motion in the steam-engine and those in the organism lies in the 

 fact that the former cannot work unless it is heated from the out- 

 side, while the latter works of itself This is wholly untrue. The 

 organism also must be heated if it is to continue in activity, i.e., in 

 life, exactly as the steam-engine. Its heating is by the introduction 

 of food. The analogy between the heating of the steam-engine and 

 the nutrition of the organism goes very far. The carbon-containing 

 food is burned in the organism in great part as is the coal in the 

 steam-engine — i.e., the food-stuffs are oxidised by the oxygen taken 

 in in respiration, as the coal is oxidised — and in both cases there is 

 obtained as the end-product carbonic acid. If the introduction of 

 food be interrupted, the activity of the organism ceases after a 

 time when all the ingested food is consumed, similarly as with the 

 steam-engine ; in both, movement is stopped. 



The comparison of the organism with the steam-engine allows 

 the untenableness of the claim of another difference, closely 

 associated with the previous one, to be at once recognised. It 

 has been said, namely, that organisms are in dynamical equi- 

 librium — i.<;., the same quantity of energy that is introduced 

 into the organism leaves it again in some form — while in- 

 organic bodies are in stable equilibrium. It is true that organ- 

 isms in the adult state are in dynamical equilibrium. But, when 

 this is put forward as a real difference in comparison with 



