IN THE ANIMAL ORGANISM. 231 



wonderful and wise economy has destined for the 

 nourishment of the animal only such compounds as 

 have a composition identical with that of the organs 

 which generate force, that is, with the muscular 

 tissue. The expenditure of force which the living 

 parts of animals require, in order to reproduce 

 themselves from the blood ; the resistance of the 

 chemical force which has to be overcome in the 

 azotised constituents of food by the vital agency of 

 the organs destined to convert them into blood ; 

 these are as nothing compared to the force with 

 which the elements of carbonic acid are held to- 

 gether. A certain amount of force would necessa- 

 rily be prevented from assuming the form of mov- 

 ing power, if it were to be expended in overcoming 

 chemical resistance ; for the momentum of motion 

 of the vital force is diminished by all obstacles. But 

 the conversion of the constituents of blood into mus- 

 cular fibre (into an organ which generates force) is 

 only a change of form. Both have the same com- 

 position ; blood is fluid, muscular fibre is solid blood. 

 We may even suppose that this change takes place 

 without any expenditure of vital force ; for the mere 

 passage of a fluid body into the solid state requires 

 no manifestation of force, but only the removal of 

 obstacles, w^hich oppose that force (cohesion), which 

 determines the form of matter, in its manifestations. 

 In what form or in what manner the vital force 

 produces mechanical effects in the animal body is 

 altogether unknown, and is as little to be ascer- 



