One might say, for example, that a patient has a kind of St Vitus's dance; a kind of dropsy; a kind of nerve fever; a kind of ague. One would never say, however (to end once and for all the confusion of these names) He has St. Vitus's dance, He has nerve fever, He has dropsy, He has ague, since there simply are not any fixed, unchanging diseases to be known by such names.