impression is usually made by what may be described as the crests of the mountain ridges of the pattern ; a strong pressure will show the connecting cols as well, so the latter are unimportant. Decipherment is a peculiar art. Gross differences are conspicuous enough to an untrained eye, but even in these a novice may sometimes contrive to make mistakes when an imperfect impression is submitted to him. On the other hand, the art of taking good prints is very easy, and may be learnt in a single lesson by any intelligent and handy man.
Much has been written, but the last word has not been said, on the rationale of these curious papillary ridges ; why in one man and in one finger they form whorls and in another loops. I may mention a characteristic anecdote of Herbert Spencer in connection with this. He asked me to show him my Laboratory and to take his prints, which I did. Then I spoke of the failure to discover the origin of these patterns, and how the fingers of unborn children had been dissected to ascertain their earliest stages, and so forth. Spencer remarked that this was beginning in the wrong way ; that I ought to consider the purpose the ridges had to fulfil, and to work backwards. Here, he said, it was obvious that the delicate mouths of the sudorific glands required the protection given to them by the ridges on either side of them, and therefrom he elaborated a consistent and ingenious hypothesis at great length.
I replied that his arguments were beautiful and deserved to be true, but it happened that the mouths of the ducts did not run in the valleys between the crests, but along the crests of the ridges themselves. He