HELMHOLTZ IN BERLIN 



belonging to the vegetable world, and causes them to 

 reunite with the oxygen of the atmosphere. Parallel 

 to this process runs the work done by animals. This 

 work is the aim and end of animal existence. Plants 

 certainly produce mechanical effects, but it is evident 

 that for equal masses and times the sum of the effects 

 produced by a plant is vanishingly small compared 

 with those produced by an animal. While, then, in 

 the plant the production of mechanical effects plays 

 quite a subordinate part, the conversion of chemical 

 tensions into useful mechanical effect is the character- 

 istic sign of animal life. In the animal body chemical 

 forces are perpetually expended. Ternary and qua- 

 ternary compounds undergo, during the life of the 

 animal, the most important changes, and are, for the 

 most part, given off in the form of binary compounds, 

 as burnt substances. The magnitude of these forces, 

 with reference to the heat developed in these processes, 

 is by no means determined with sufficient accuracy ; 

 but here, where our object is simply the establishment 

 of a principle, it will be sufficient to take into account 

 the heat of combustion of the pure carbon. When 

 additional data have been obtained, it will be easy 

 to modify our numerical calculations so as to render 

 them accordant with the new facts.' 



(He then goes on with calculations.) 



' If the animal organism applied the disposable com- 

 bustible material solely to the performance of work, 

 the quantities of carbon just calculated would suffice 

 55 



