222 INSTINCT : 



tions of viscera take place automatically, and even in 

 response to unfelt impressions. 



But now let us glance at other incidents in association 

 with these visceral impressions and actions. 



No * needs ' or ' appetites ' exist in connection with the 

 action of the Heart, for the very simple reason that its 

 stimulus is always at hand, and, in the form of arterial or 

 venous blood, actually flows into the several cardiac cham- 

 bers, after each contraction. It is a little different with 

 regard to the Respiratory Organs. Aerated water or pure 

 air does not always surround the organism; and, as a 

 consequence of this occasional absence of the proper stimu- 

 lus, it is found that under such unnatural conditions a 

 * respiratory need,' or want, is felt. Owing, however, to 

 this being a want of accidental, rather than of regular, 

 occurrence, it never attains the more definite and more 

 regularly-recurrent character of an * appetite.' 



How different is it with the Alimentary Canal. Its par- 

 ticular stimulus is not ever present like that of the heart, 

 or only occasionally absent, as with that of the respiratory 

 organs ; it mostly has to be sought. Hence it is that 

 the habitually recurring need reveals itself as a defi- 

 nitely returning appetite for food. Much the same kind 

 of origin is to be ascribed to the sexual appetite, except 

 that it is one which, in organisms generally, recurs at 

 more or less distant intervals. Just as hunger, however, 

 depends, almost wholly, upon impressions coming from 

 the alimentary canal, so does the sexual appetite depend, 

 in the main, upon particular states of certain Generati\e 

 Organs. 



Any one, who carefully studies the acts of lower animals, 

 will readily recognize how very large a proportion of them 

 are, either immediately or remotely, instigated by one or 

 other of these visceral needs or ' appetites.' 



