Hume in 1739 and again in 1748 appealed to everyday observation of dogs, birds, and other animals of high grade. The facts seemed to him to show that animals as well as men are endowed with reason and able to draw inferences; he did not, however, credit them with the power of framing general statements, holding that experience operates on them, as on children and the generality of mankind, by "custom" alone. It is notorious that the dog and other higher animals learn by experience; Hume tells, for instance, how an old greyhound will leave the more fatiguing part of the chase to younger dogs, and place himself so as to meet the hare in her doubles. On the other hand (though Hume does not say so) man himself possesses non-educable instincts. In short, Hume sees no ground for drawing a line between the mental powers of man and those of the higher animals, though he attributes to man a power of demonstrative reasoning to which animals do not attain. In this he substantially agrees with Aristotle,[28] who maintained that in animals the germs of the psychical qualities of the man are evident, though, as in the child, they are undeveloped. Hume's teaching also accords with modern views; comparative anatomy, for instance, "is easily able to show that, physically, man is but the last term of a long series of forms, which lead by slow gradations from the highest mammal to the almost formless speck of living protoplasm, which lies on the shadowy boundary between animal and vegetable life."[29]