The most complex sound made by them is the one elsewhere described as meaning "good." They often use it in a sense very much the same as mankind uses the word "thanks," but it is not probable that they use it as a polite term, yet the same idea is present.
One of the words of warning or alarm contains a vowel element closely resembling the short sound of "e." It terminates with the breathing sound of "h." It is used to announce the approach of anything that he is familiar with, and not afraid of. If the sound is intended to warn against the approach of an enemy, or something strange, the same vowel element is used, but terminates with the aspirate sound of "h" pronounced with energy and distinctness. The two words are the same in vowel quality, but they differ in the time required to utter them, and the final breathing and aspirate effects. There is also a difference in the manner of the speaker in the act of delivering the word, which plainly indicates that he knows the use and value of the sounds. At the approach of danger the latter is often given almost in a whisper, and at long intervals apart, but increases in loudness as the danger approaches; the other is usually spoken distinctly and repeated frequently. It is worthy of note that the native tribes often use the same word in the same manner and for the same purpose.
There are other sounds which are easily identified but difficult to describe, such as that used to signify "cold" or "discomfort"; another for "drink"; another referring to "illness," and still another which I have good reason to believe means "dead" or "death." There are perhaps a dozen more that I can distinguish, but have not yet been able to determine their meaning. I have an opinion as to some of them which I have not yet verified.
The chimpanzee makes use of a few signs which seem to be fixed factors of expression. He makes a negative sign by moving the head from side to side, but the gesture is not frequent or pronounced. Another negative sign, which is more common, is a motion of the hand from the body towards the person or thing addressed. This sign is sometimes made with great emphasis, and there can be no question as to what it means. The manner of making the sign is not uniform. Sometimes it is done by an urgent motion of the hand. Bringing it from his opposite side, with the back forward, it is waved towards any one approaching, if the ape object to the approach. The same sign is often made as a refusal of anything offered him. Another way of making this sign is with the arm extended forward, the hand hanging down, and the back towards the person approaching or the thing refused. In addition to these negative signs there is one which may be regarded as affirmative. It is made simply by extending one arm towards the person or thing desired. It sometimes serves the purpose of beckoning; but in this act there is no motion of the hand. These signs are similar in character to those used by men, and appear to be innate.
It must not be inferred from this small list of words and signs that there is nothing left to learn. So far we have only taken the first step as it were in the study of the speech of apes. As we grow more familiar with their sounds, it becomes less difficult to understand them. I have not been disappointed in what I hoped to learn from these animals. The total number of words in the speech of all simians that I have learned up to this time is about one hundred. I have given no attention of late to the small monkeys, but I shall resume the task at some future day, as it forms a part of the work I have assumed, but all of that is described in a work already published.
In conclusion, I will say that the sounds uttered by these apes have all the characteristics of true speech. The speaker is conscious of the meaning of the sound used, and uses it with the definite purpose of conveying an idea to the one addressed; the sound is always addressed to some definite one, and the speaker usually looks at the one addressed; he regulates the pitch and volume of the voice to suit the condition under which it is used; he knows the value of sound as a medium of thought. These and many other facts show that they are truly speech.
If these apes were placed under domestication, and kept there as long as the dog has been, he would be as far superior to the dog in sagacity as he is by nature above the wild progenitors of the canine race.