| Under 1 year | 2 | At 7 years | 23 | At 16 years | 6 |
| At 2 years | 6 | At 8 years | 24 | At 17 years | 10 |
| At 3 years | 4 | At 9 years | 31 | At 18 years | 5 |
| At 4 years | 7 | At 10 years | 23 | At 19 years | 5 |
| At 5 years | 9 | At 11 years | 18 | At 20 years | 1 |
| At 6 years | 24 | At 12 years | 25 | At 21 years | 3 |
| At 22, 25, 27, 28, 35, 38, 82, and 86 years, each 1 case. | |||||
Sex exerts considerable influence on the disease. Sée states that three-fourths of all the cases observed in the Children's Hospital in Paris occurred in girls. Of 328 cases which I have examined in reference to this point, 232 were females and 96 males.
Social condition has little or no effect on the production of chorea, but it is more common in cities than in the country. Indeed, everything which increases the excitability of the nervous system during development adds to the tendency to the disease.
West and Hamilton point to over-study as a cause, and I have frequently verified their observations. The annual examinations at our public schools give a number of cases of chorea.
A. McLane Hamilton7 has recently investigated the frequency of St. Vitus's dance among school-children in New York, and found that 20 per cent. of the children in the schools were affected with some variety of the disorder.
7 American Psychological Journal, Feb., 1876.
Rheumatism is certainly a predisposing cause, in my experience, but I have not found it associated with chorea as frequently as some authors have. In 279 cases which I examined with regard to this question, there was a clear history of rheumatism in but 37. Cardiac complications were much more frequent. In 82 cases there was a cardiac murmur heard. In some of these the murmur was no doubt anæmic, but in the majority there had probably been a rheumatic endocarditis. Many cases in which there is said by the friends of the patient to have been a previous attack of acute rheumatism, on investigation are found not to have had articular rheumatism, but merely some muscular or joint pains which were not inflammatory. Quite recently Joffroy and Saric have expressed the opinion that the pains in the joints during an attack of chorea are to be regarded as choreal arthropathies of nervous origin.
English and French writers have observed the relation between rheumatism and chorea in a large proportion of cases. Hughes and Burton Brown8 found that in 104 cases which they examined as to rheumatism and affections of the heart, there were but 15 in which some rheumatic condition had not preceded the attack or a cardiac murmur did not exist.
8 Guy's Hospital Reports, 1856.