PHYSIOLOGICAL INTEGRATION IN ANIMALS. 307 



indeed, we see the relation under another aspect. This more 

 rapid rhythm of the functions which increased heterogeneity 

 of structure makes possible, is itself a means of integrating 

 the functions. Watch, when it is running down, a compli- 

 cated machine of which the parts are not accurately adjusted, 

 or are so worn as to be somewhat loose. There will be 

 observed certain irregularities of movement just before it 

 comes to rest — certain of the parts which stop first, are 

 again made to move a little by the continued movement 

 of the rest, and then become themselves, in turn, the 

 causes of renewed motion in other parts which have ceased 

 to move. That is to say, while the connected rhythmical 

 changes of the machine are quick, their actions and re- 

 actions on one another are regular — all the motions are well 

 integrated ; but as the velocity diminishes, irregularities arise 

 — the motions become somewhat disintegrated. Similarly 

 with organic functions : increase of their rapidity involves 

 increase of a joint momentum which controls each and co- 

 ordinates all. Thus, if we compare a Snake with a Mammal, 

 we see that its functions are not tied together so closely. 

 The Mammal, and especially the superior Mammal, requires 

 food with considerable regularity ; keeps up a respiration 

 that varies within but moderate limits ; and has periods of 

 activity and rest that alternate evenly and frequently. But 

 the Snake, taking food at long intervals, may haA^e these 

 intervals greatly extended without fatal results ; its dormant 

 and its active states recur less uniformly ; and its rate of 

 respiration varies within much wider limits — now being 

 scarcely perceptible, and now, as you may prove by exciting 

 it, becoming conspicuous. So that here, where the rhythms 

 are very slow, they are individually less regular, and are 

 united into a less regular compound rhythm — are less in- 

 tegrated. 



Perhaps the clearest general idea of the co-ordination of 

 functions that accompanies their specialization, is obtained by 

 observing the slowness with which a little-differentiated animal 



