when spoken to unless specially taught.  A much slighter degree of deafness will prevent the proper acquisition of speech and language than would in later life prevent the comprehension of conversation in a familiar language.  As even the child of fifteen months would benefit from some modifications of the ordinary treatment of a baby, if his hearing was not normally acute, it is to his advantage to have the fact of his deafness known at once by those in charge of him.

It is not as easy as it might seem to the inexperienced to determine even approximately the situation of a fifteen-months-old baby with respect to its hearing.  Our interest here is, of course, in the tests of hearing that do not require special apparatus and special training.  In the case of a child less than two years of age we must rely upon merely attracting his attention by various sounds, judging the effect upon him by his expression and actions.  We cannot, at that age, establish a system of responses, nor expect him to imitate the sounds he hears.  Sounds should be used for testing that disturb only the air, and are not sufficiently low and powerful to set in vibration the floor, chair, or any other object with which he may be in contact.  Deaf children rapidly become abnormally sensitive to vibrations, which are to them what noises are to us.  A rather smooth, not too shrill, whistle is one excellent sound to use.  Not a fluttering whistle like the postman’s, nor a heavy tone like an organ pipe or bass horn.  Clapping the hands is a good initial test of a crude nature; then a moderate whistle, varying the pitch, for sometimes high sounds are perceived, but not low ones, or vice versa.  Then a bell, such as a small table bell, the telephone, electric door bell, etc.  Lastly, the human voice in various pitches, volumes, distances, and vowels.  Little by little it can be determined whether the child hears all the sounds, and if not, then which, if any, he perceives.  A totally deaf child may often deceive the investigator by turning his head at the critical moment, apparently in response to the sound that was made, while, on the other hand, a child very slightly deaf, or not deaf at all, may completely ignore the sounds made for the purpose of attracting his attention.  Therefore, it takes time and repeated tests under varying environments to gradually eliminate possible errors and coincidences.

It must be remembered that the intensity with which a sound affects the ear varies inversely as the square of the distance from the ear to the source of the sound.  That is to say, if exactly the same sound is repeated at half the distance, the intensity with which it reaches the ear is four times as great as before, and if the distance is quartered, the intensity is sixteen times as great.  In other words, if “ah” is spoken with a certain loudness eight inches from the child’s ear, and then again with exactly the same pitch and volume only two inches from his ear, it will be sixteen times as loud to him as it was the first time.