Distribution.—We are only in posses sion of information as to the distribution of deaf-mutism in Europe, the United States of America, and some European colonies. Not even all European coun tries have undertaken an enumeration of their deaf-mute population; Russia, the largest of them, having, for instance, no deaf-mute statistics. The table on page 439, which includes the most recent enumeration of deaf-mutes, gives their numbers in different countries, also the proportion of males and females.
It will be seen from this table that deaf-mutism is very variously distributed in the countries from which we possess statistics. The causes of the remark ably unequal geographical distribution of deaf-mutism, which will be seen from the table, are probably numerous and various. To begin with, we are involun tarily struck by the fact that the Euro pean countries, with large deaf-mute population, are the most Mountainous, which is in perfect accord with the fact that deaf-mutism is more frequent in mountainous that in lowland districts. I shall later on have occasion to point out that this is not, in all probability, the result of great altitudes and peculiar geo logical formations, but of the unfavor able social and hygienic conditions com mon to mountainous countries (consan guinity, poverty, unhealthy dwellings, etc.), the importance of which as causes of deaf-mutism will be discussed after ward. Further, wide-spread and malig nant epidemics of cerebrospinal menin gitis, an important cause of deaf-mutism, explain the frequency of this condition in the lowland countries of Central Europe.
Ilre must, also, observe that the coun tries in the west and south of Europe are the most fertile and productive, while those in the north and centre are less favorably endowed by nature. That this circumstance is a factor in the distribu tion of deaf-mutism has been proved by investigations made in different districts in Denmark, and especially in Saxony. Finally, the northern and central coun tries are, on the whole, the most thinly populated in Europe, doubtless the re sult of the barrenness of the soil.
Sex.—The table on page 439 shows a greater frequency of deaf-mutism among males than females, the difference in sev eral countries being considerable. The number of female deaf-mutes per 100 male deaf-mutes varies, according to the table, from 94 in Bavaria to 65 in Spain, the average rate in Europe and the United States of America, being 82 fe males per 100 males. The numerical superiority of male deaf-mutes is the more remarkable since females are more numerous than males in nearly all the European countries, Italy being the only country of those mentioned in the table which exhibits a slight inferiority as re gards the female population. This nu merical superiority of the male deaf mutes must undoubtedly be considered principally as an expression of the greater liability the male organ of hear ing has to be morbidly affected.
Symptoms and Sequelae.—Of the symp toms, the principal are, of course, deaf ness and dumbness; but other symptoms closely connected with the ear disease causing deafness are often met with in eases of deaf-mutism.
DEAFICESS.—The term "deafness" is not only used to express the absolute ab sence of hearing,—total deafness,—but also to express a condition in which some traces of hearing remain, but in which the human voice is not audible in the usual way: a condition to be described as partial deafness. From a theoretical
point of view, it seems an easy matter to make a sharp distinction between the condition in which the auditory nerve is entirely out of function and that in which it still acts, though deficiently. As a matter of fact, however, it has been proved that it is sometimes difficult to decide, in particular cases, whether there are any remains of hearing or not; and, further, the results of these two condi tions (if acquired in early infancy or congenital) are the same, viz.: deaf mutism. In other words, both subjects with total deafness and those with par tial deafness may be met with among deaf-mutes.
It is not always an easy matter to test and decide the amount of hearing pos sessed by a child, especially an infant. As a rule, only ordinary loud sources of sound can be employed to discover whether the child in question reacts in any way to the sound produced; for instance, by turning or blinking its eyes. Generally, a loud whistle, a bell, clap ping the hands, or such like devices are made use of. Such a rough mode of ex amination can, however, only decide whether the power of hearing exists or not in individual cases, and even this is often difficult when the patient is an infant, and it is also no easy matter to determine whether the power of hearing is equal on both sides. With older chil dren it is easier to discover whether the power of bearing exists, and, if so, in what degree. In the latter case less pow erful sources of sound may be employed. Of these the principal is the tuning-fork, the vibrations of which are used in meas uring the conduction of sound through the middle ear, by placing it outside the ear; and also in measuring the so called bone, or cranio-tympanic, con duction, by placing it on the mastoid process or on the teeth. The human voice is also an important means of in vestigation. The best means of employ ing it is by pronouncing certain vowels loudly and distinctly close to the deaf mute's ear, without his being able to see 1 the movement of the lips, the patient being asked to repeat the vowels pro nounced. To prevent the possibility of guessing the vowels should be repeated several times. If the deaf-mute under stands the vowels easily, consonants and even words and short sentences'may be tried. In most cases this method can only be made use of when the deaf-mute in question has learned to articulate. A greater power of hearing is seldom met with, unless sound-increasing apparatus are employed. The hearing of deaf mutes with considerable remains of hear ing can also be tested with a loud-ticking watch placed outside the ear or pressed against the outer ear. It is, however, very -unusual for deaf-mutes to be able to distinguish the high notes represented by the ticking of a watch. In employing all these methods, it must be remem bered that the hearing of deaf-mutes dif fers greatly at different times in some cases, according to varying conditions in the ear, of which we have no immediate knowledge.