THE RE- ACTIONS OF ORGANIC MATTER ON FORCES. 53 



experiments on nerves — experiments which show that nerve- 

 force is generated when th'e cut end of a nerve is either me- 

 chanically irritated, or acted on by some chemical agent, or 

 subject to the galvanic current — experiments which thus 

 prove that nerve-force is liberated by whatever disturbs the 

 molecular equilibrium of nerve-substance. And this is all 

 which it is necessary for us here to understand. 



§ 22. The most important of these re-actions called forth 

 from organisms by surrounding actions, remains to be noticed. 

 To the above various forms of insensible motion thus caused, 

 we have to add sensible motion. On the production of this 

 mode of force, more especially depends the possibility of all 

 vital phenomena. It is, indeed, usual to regard the power of 

 generating sensible motion, as confined to one out of the two 

 organic sub-kingdoms ; or, at any rate, as possessed by but 

 few members of the other. On looking closer into the matter, 

 however, we see that plant-life as well as animal-life, is uni- 

 versally accompanied by certain manifestations of this power ; 

 and that plant-life could not otherwise continue. 



Through the humblest, as well as through the highest, ve- 

 getal organisms, there are ever going on certain re-distribu- 

 tions of matter. In protophytes the microscope shows us an 

 internal transposition of parts, which when not active enough 

 to be immediately visible, is proved to exist by the changes 

 of arrangement that become manifest in the course of hours 

 and days. In the individual cells of many higher plants, an 

 active movement among the contained granules may be wit- 

 nessed. And well-developed cryptogams in common with all 

 phanerogams, exhibit this genesis of mechanical motion still 

 more conspicuously in the circulation of sap. It might, in- 

 deed, be concluded d priori^ that through plants displaying 

 much differentiation of parts, an internal movement must be 

 going on ; since, without it, the mutual dependence of organs 

 having unlike functions would seem impossible. Be- 



sides these motions of fluids kept up internally, plants, espe- 



