THE FORMATION OF A DEAF VARIETY OF THE HUMAN RACE. 213 



There are indications also of a similar though less disturbance inthe numbers of those who 

 lost their hearing from disease during the decade 1811 to 1820. An examination of the reports of 

 the American Asylum and Illinois institution may throw light upon the nature of these disturb- 

 ances. By classifying the pupils of these institutions according to their period of birth, we obtain 

 the results that are<exhibited graphically in the foregoing diagram (Fig, 9). 



The apparent decrease in the number of pupils 'born in the last two decades is susceptible of 

 simple explanation. Very few pupils are received into institutions for the deaf and dumb'before 

 they are ten or twelve years of age, while it is not uncommon for pupils to be admitted at twenly^ 

 or twenty -five years of age or even older. 



A pupil born in the year 18G9 would only be 13 years of age in 1882 (the date of the Illinois 

 report). It is evident, therefore, that of those deaf mutes who were born in 'the decade 1860 to 

 1801) who will ultimately make their appearance in the Illinois institution all had not been received 

 at the date of the report. 



A similar explanation can be given in the case of the American Asylum. The dotted lines 

 indicate those portions of the curves which are known to be inaccurate on this account. 



In regard to the American Asylum the abnormal increase in the number of pupils who became 

 deaf from disease or accident who were born during the decade 1810-'19 is very marked. Another 

 abnormal increase is observable in the number of those who became deaf in the decade 1860-'69. 

 Indeed, the relations of the congenital and non-congenital deaf-mutes are reversed in a similar 

 manner to that shown in Fig. 8. In regard to the Illinois pupils (see Fig. 9) it will be observed 

 that the increase in the numbers of the nou-congenitally deaf is so enormous, that of the pupils who 

 were born in the decade 1860-'69 there were more than three times as many non-conaenitally deaf 

 as there were congenitally deaf, and of those born iu 1870-'79 more than four times, whereas the 

 census retui'us show that more than half of all the deaf-mutes living in this country (1880) were 

 born deaf. 



In the reports of the American Asylum and Illinois institutions the year when each pupil was 

 admitted and his age when admitted are noted, with few exceptions. From these elements the 

 period of birth has been calculated. The period when hearing was lost has also been ascertained 

 iu all cases where the age of the pupil when deafness occurred is stated in the report. 



In tables K and L of the Appendix the non-congenital pupils of both institutions are class- 

 itied according to the period when hearing was lost and according to the disease that caused 

 deafness. In regard to the Illinois report it is unfortunately the case that the age of the pupil 

 when deafness occurred is not stated in 327 cases out of 947, so that we are only able to classify 

 about two-thirds of the cases in this way. The results are shown graphically in the upper dia- 

 grams of Fig. 10. 



From the tables in the Appendix we have clear evidences of two epidemics of "spotted fever "• 

 or epidemic cerebrospinal meningitis. One epidemic during the decade 1810 to 1819, reaching a 

 maximum in the year 1815, and the other (a great epidemic) iu the decade 18C0 to 1809, continuing 

 in the last decade, 1870 to 1879. 



The pupils who became deaf from cerebro-spinal meningitis and from scarlet fever are clas- 

 sified according to the period when deafness occurred in the lower diagrams of Fig. 10. 



The numbers of the nim-congmitaUij deaf are evidently subject to great and sudden fluctuations on 

 account of epidemicaJ diseases which cause' deafness, whereas the growth of the congenitally-deafpopula- 

 tioti seems to be much more regular. 



•According to Dr. Kussell Reynolds "spotted fever" is a popular name for epidemic cerebro-spinal meningitis. 

 See "A System of Medicine," 18H0, Vol. I, pp. 296-7. 



