PHYSIOLOGICAL INTEGRATION IN ANIMALS. 375 



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 reactions 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 con- 

 siderable regularity; keeps up a respiration which 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 have 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 per- 

 ceptible 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 integrated. 



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 responds to a stimulus applied to one of its parts, 



