42 THE DATA OF BIOLOGY. 



and parts of organisms where the activity is least, such 

 changes as do take place are initiated by a substance contain- 

 ing nitrogen. Does it not seem probable, then, that these 

 extremely unstable compounds have everywhere the effect of 

 communicating to the less unstable compounds associated 

 with them, molecular movements towards a stable state, like 

 those they are themselves undergoing? The changes which 

 we thus suppose nitrogenous matter to produce in the body, 

 are clearly analogous to those which we see it produce out of 

 the body. Out of the body, certain carbo-hydrates in con- 

 tinued contact with nitrogenous matter, are transformed into 

 carbonic acid and alcohol, and unless prevented the alcohol 

 is transformed into acetic acid: the substances formed 

 being thus more highly oxidized and more stable than the 

 substances destroyed. In the body, these same carbo- 

 hydrates, in continued contact with nitrogenous matter, are 

 transformed into carbonic acid and water: substances which 

 are also more highly oxidized and more stable than those 

 from which they result. And since acetic acid is itself re- 

 solved by further oxidation into carbonic acid and water; 

 we see that the chief difference between the two cases is, 

 that the process is more completely effected in the body than 

 it is out of the body. Thus, to carry further the simile used 

 above, the molecules of carbo-hydrates contained in the tis- 

 sues are, like bricks on end, not in the stablest equilibrium ; 

 but still in an equilibrium so stable, that they cannot be 

 overthrown by the chemical and thermal forces which the 

 body brings to bear on them. On the other hand, being like 

 similarly-placed bricks that have very narrow ends, the nitro- 

 genous molecules contained in the tissues are in so unstaWe 

 an equilibrium that they cannot withstand these forces. 

 And when these delicately-poised nitrogenous molecules 

 fall into stable arrangements, they give impulses to the 

 more firmly-poised non-nitrogenous molecules, which cause 

 them also to fall into stable arrangements. It is a 



curious and significant fact that in the arts, we not only 



