The first step in the growth of the book was taken when _memory aids_ were invented. Sometimes we tie a knot in a handkerchief to help us to remember something. Now, it was just by tying knots that primitive man first lent assistance to the memory. The first material book was doubtless a series of _knots_ well represented by the _quipu_ (Fig. 2) of the ancient Peruvians. This curious-looking book was written (tied) by one known as the officer of the knots. It contains an account of the strength of the Peruvian army, although it is confessed that its exact meaning cannot be made out. It was not intended to be read by any one who was not a keeper of the knots. Books made of knots were used by nearly all the ancient peoples of South America and by some of those of Asia. Akin to the knotted cord is the _notched stick_, which is still used in Australia by the savages to assist the memory of one who has a message to carry. Figure 3 shows a variety of such message-sticks. The lowest one--a crooked branch of a tree--contains an invitation to a dancing party. The notches are read by the messenger. The notched stick as an aid to memory is not confined to savage races. Many a highly civilized baker has kept his accounts by making notches in sticks and so has many a modern dairyman, as he has delivered milk from door to door. [Illustration: FIG. 2.--THE QUIPU OF THE PERUVIANS.] [Illustration: FIG. 3.--MESSAGE-STICKS.] Memory aids were followed by _picture-writing_. To express thought by means of pictures is an instinct shared alike by the lowest savage and the most enlightened people. All over the earth we find examples of early picture-writing. A beloved chief had died, a fierce battle had been fought, an exciting chase had occurred: promptly the event was pictured on a stone or on the skin of some animal. Pages might be filled with illustrations of these primitive picture-books, but we must be content with a single specimen (Fig. 4). This was found painted on a rock in California: "_We selected this as a camping place, but we have found nothing_," say the human figures _f_, _g_, _h_, _i_. The upturned palms say plainly, "nothing, nothing." "_One of our comrades_ (_d_) _has died of starvation_," say the three lank figures at _c_ pointing to their own lean bodies. "_We deeply mourn his loss_," says the sorrow-stricken _a_. "_We have gone northward_," says _j_, his distinguished arm extended to the north. [Illustration: FIG. 4.--PICTURE WRITING.]