On one occasion I visited the Zoölogical Garden in Cincinnati, where I found in a cage a small Capuchin to whom I gave the name Banquo. It was near night and the visitors had left the house. The little monkey, worried out by the annoyance of visitors, sat quietly in the back of his cage, as though glad that another day was done. I approached the cage and uttered the sound which I have translated “drink.” The first effort caught his attention and caused him to turn and look at me. He rose and answered with the same word. He then came to the front of the cage and looked at me as if in doubt. I repeated the word. He again responded, and turned to a small pan in the cage. He took it up and placed it near the door through which the keeper passed food to him. He then turned to me and again uttered the word. I asked the keeper for some milk; but he brought me some water instead. The efforts of the little simian to secure the glass were very earnest, and his pleading manner and tone gave evidence of his thirst. I allowed him to dip his hand into the glass and lick the water from his fingers. When the glass was kept out of the reach of his hand he repeated the sound and looked beseechingly at me as if to say: “Please give me more.” This caused me to suspect that the word which I had translated “milk” also meant “water.” From this and other tests I finally determined that it meant “drink” in a broad sense and possibly also meant “thirst.” It evidently expressed his desire for something with which to allay his thirst. The sound is very difficult to imitate and quite impossible to write, but an idea of it is given elsewhere. On one of my visits to the Chicago Garden I stood with my side to a cage containing a small Capuchin. I uttered the sound which had been translated “milk.” It caused him to turn and look at me, and on my repeating the sound a few times he answered very distinctly, using the same sound. Picking up the pan from which he usually drank, he brought it to the front of the cage, set it down, came up to the bars, and distinctly uttered the word. He had not been shown any milk or other kind of food. The man in charge then brought some milk, which I gave to the monkey, who drank it with great delight. I again held up his pan and repeated the sound. He used the same sound each time when he wanted milk. During this visit I tried many experiments with the word which I am now convinced means “food” or “hunger.” I was led to the belief that he used the same word for apple, carrot, bread, and banana. Later experiments, however, have caused me to modify this view, because the phonograph shows slight variations of the sound, and it is probable that these faint inflections may indicate different kinds of food. They usually recognize this sound, even when poorly imitated. In this word may be found a clue to the great secret of speech. And while I have taken but one short step toward its solution, these facts point out the way that leads to it.