IV. CAUSES OF DEAFNESS IN NEW YORK INSTITUTION FROM 1818 TO 1853 AND FROM 1899 TO 1912.
| PERIOD | TOTAL NUMBER | CONGENITAL | SCARLET FEVER | MENINGITIS | TYPHOID FEVER | MEASLES | WHOOPING COUGH | GENERAL FEVERS | BRAIN FEVER | PNEUMONIA | DIPHTHERIA | CATARRH | UNKNOWN AND MIS. |
| 1818‑1853 | 1148 | 42.9 | 7.2 | —[39] | — | 1.9 | 0.7 | 1.6 | — | — | — | — | 45.7 |
| 1899‑1912 | — | 38.0 | 6.8 | 13.1 | 1.3 | 3.4 | 0.8 | 1.3 | 8.1 | 0.9 | 0.9 | 1.7 | 23.7 |
Taking these tables also collectively, we find in respect to scarlet fever a decline in all the schools, this being especially pronounced in the case of the Ohio. In meningitis, however, there is an increase so heavy as to call in question the accuracy of the earlier records; and it is possible that it failed to be entirely recognized then. In most of the other diseases, as in the previous case, no very great change is perceptible. In general fevers a decline is apparent in all, in most being considerable; and probably several diseases were formerly included which are now listed separately. In measles rather a decline is found in the American and Ohio schools, but a slight increase in the Iowa, and a somewhat larger one in the New York Institution. In typhoid fever there is a slight increase also in the Iowa School, but a decrease in the Ohio. In brain fever a considerable increase is observed in the Iowa School, but a slight decrease likewise in the Ohio. In whooping cough there is an increase in the New York Institution and the Iowa School, but a decrease in the American. Such diseases as pneumonia, diphtheria and catarrh seem not usually to have been separately classified in the past, though in the Ohio School we find diphtheria noted, and with somewhat smaller proportions than in later years; while in several of the schools we find "colds" given in former times, which may have been in part really catarrh.
Combining now the results of our two groups of tables, we may be able to reach some conclusions with respect to the increase or decrease of deafness from certain diseases, though on the whole far less definite than we could wish. In the first place, it seems safe to affirm that deafness from scarlet fever is becoming relatively less with the years; and it is possible that if it continues its present rate of decline, it will in time cease to be one of the main causes of deafness. On the other hand, meningitis, its great companion in evil, shows a striking increase in comparison with past years, as a cause of adventitious deafness; while its accretion may be traced as well in a series of recent years in certain schools, though not in others. But how far there is an absolute increase in meningitis over the past, and whether it is tending at present actually to increase, may be a matter for question. In view of the possibility that the disease was not sufficiently accounted for in the past, and in the absence of any knowledge to indicate a reason for its less prevalence in earlier years, at least not to the extent indicated by the statistics, it may be that its increase is, after all, more apparent than real. The fact, moreover, that in the series of recent years a marked increase is found in some schools, but a marked decline in others, may perhaps be taken to mean that at present meningitis may be on the increase only in certain sections, depending possibly on local conditions. With the greater medical skill of to-day, and with a larger proportion of children in the schools, it may be open to considerable doubt if the movement of this disease is really one of increase, though it seems that we are on the whole making no great headway against it.
As to the minor diseases causing deafness, our statistics do not indicate just to what extent and in what direction deafness from them is being affected, and no precise conclusions can at present be set down. It is probable, however, that with the increased attention to children's diseases, as we have noted, there is really less deafness from most of them than formerly.[40]
The Congenitally Deaf
When we come to consider the question of congenital deafness, which comprises a little over a third of the total amount of deafness, we have an even more difficult problem on our hands, for here we are to deal with some of the great questions of heredity—though hereditary deafness and congenital deafness are not altogether one and the same thing.[41] For the purposes of our inquiry, let us think of the congenitally deaf as divided into three great classes in respect to their family relations: 1. the offspring of parents who were cousins; 2. the offspring of parents who were themselves deaf or members of families in which there are other deaf relatives; and 3. the product of families without either consanguinity or antecedent deafness. Of these three classes the first two only will engage our attention. Of the last, comprising, according to the census, nine-twentieths, or 44.4 per cent, of the congenitally deaf, there is not much that we can say. For a great part of it there no doubt exists in the parent, or perhaps in a more remote ancestor, some abnormal strain, physical or mental, in the nature of disease or other defect. But in respect to such deafness we have too little in the way of statistical data to help us arrive at any real determination; and for it as a whole we shall have to wait till we have greater knowledge of eugenics and the laws of heredity.[42]