Every profession or trade, every art, and every science has its technical vocabulary. Different occupations, however, differ widely in the character of their special vocabularies. In trades and handicrafts, and other vocations, like farming and fishery, that have occupied great numbers of men from remote times, the technical vocabulary, is very old. It consists largely of native words, or of borrowed words that have worked themselves into the very fibre of our language. Hence, though highly technical in many particulars, these vocabularies are more familiar in sound, and more generally understood, than most other technicalities. The special dialects of law, medicine, divinity, and philosophy have also, in their older strata, become pretty familiar to cultivated persons and have contributed much to the popular vocabulary. Yet every vocation still possesses a large body of technical terms that remain essentially foreign, even to educated speech. And the proportion has been much increased in the last fifty years, particularly in the various departments of natural and political science and in the mechanic arts. Here new terms are coined with the greatest freedom, and abandoned with indifference when they have served their turn. Most of the new coinages are confined to special discussions, and seldom get into general literature or conversation. Yet no profession is nowadays, as all professions once were, a close guild. The lawyer, the physician, the man of science, the divine, associated freely with his fellow-creatures, and does not meet them in a merely professional way. Furthermore, what is called "popular science" makes everybody acquainted with modem views and recent discoveries. Any important experiment, though made in a remote or provincial laboratory, is at once reported in the newspapers, and everybody is soon talking about it---as in the case of the Roentgen rays and wireless telegraphy. Thus our common speech is always taking up new technical terms and making them commonplace.
Special words used in technical discussion ______.

All the infants died before the first year. But clearly there was more than lack of language here. What was missing was good mothering. Without good mothering, in the first year of life especially, the capacity to survive is seriously affected.
Today no such severe lack exists as that ordered by Frederick. Nevertheless, some children are still backward in speaking. Most often the reason for this is that the mother is insensitive to the signals of the infant, whose brain is programmed to learn language rapidly. If these sensitive periods are neglected, the ideal time for acquiring skills passes and they might never be learned so easily again. A bird learns to sing and to fly at the right time, but the process is slew and hard once the critical stage has passed.
Experts suggest that speech stages are reached in a fixed sequence and at a constant age, but there are. cases where speech has started late in a child who eventually turns out to be of high IQ. At twelve weeks a baby smiles and makes vowel-like sounds; at twelve months he can speak simple words and understand simple commands; at eighteen months he has a vocabulary of three to five words. At three he knows about 1,000 words which he can put into sentences, and at four his language differs from that of his parents in style rather titan grammar.
Recent evidence suggests that an infant is born with the capacity to speak. What is special about man’s brain, compared with that of the monkey, is the complex system which enables a child to connect the sight and feel of, say, a toy-bear with the sound pattern "toy bear". And even more incredible is the young brain’s ability to pick out an order in language from the mixture of sound around him, to analyse, to combine and recombine the parts of a language in new ways.
But speech has to be induced, and this depends on interaction between the mother and the child, where the mother recognises the signals in the child’s babbling(咿哑学语) , grasping and smiling, and responds to them. Insensitivity of the mother to these signals dulls the interaction because the child gets discouraged and sends out only the obvious signals. Sensitivity to the child’s non-verbal signals is essential to the growth and development of language.