T 2.1.12.8

There are also instances of the relation of impressions, sufficient to convince us, that there is an union of certain affections with each other in the inferior species of creatures as well as in the superior, and that their minds are frequently convey'd thro' a series of connected emotions. A dog, when elevated with joy, runs naturally into love and kindness, whether of his master or of the sex. In like manner, when full of pain and sorrow, he becomes quarrelsome and ill-natur'd; and that passion, which at first was grief, is by the smallest occasion converted into anger.