“The subject of this observation is a girl aged four and a half years, sprightly, intelligent, and in good health. The mother observed, when she was two years old, that she was backward in speaking, and only used the words ‘papa’ and ‘mamma.’ After that she began to use words of her own invention, and though she understood readily what she said, never employed the words used by others. Gradually she enlarged her vocabulary until it has reached the extent described below. She has a brother eighteen months younger than herself, who has learned her language, so that they can talk freely together. He, however, seems to have adopted it only because he has more intercourse with her than the others; and in some instances he will use a proper word with his mother, and his sister’s word with her. She, however, persists in using only her own words, though her parents, who are uneasy about her peculiarity of speech, make great efforts to induce her to use proper words. As to the possibility of her having learned these words from others, it is proper to state that her parents are persons of cultivation, who use only the English language. The mother has learned French, but never uses the language in conversation. The domestics, as well as the nurses, speak English without any peculiarities, and the child has heard even less than usual of what is called baby-talk. Some of the words and phrases have a resemblance to the French; but it is certain that no person using that language has frequented the house, and it is doubtful whether the child has on any occasion heard it spoken. There seems to be no difficulty about the vocal organs. She uses her language readily and freely, and when she is with her brother they converse with great rapidity and fluency. “Dr. Hun then gives the vocabulary, which, he states, was such as he had ‘been able at different times to compile from the child herself, and especially from the report of her mother.’ From this statement we may infer that the list probably did not include the whole number of words in this child-language. It comprises, in fact, only twenty-one distinct words, though many of these were used in a great variety of acceptations, indicated by the order in which they were arranged, or by compounding them in various ways....