There is much that is obscure with reference to the nature both of rheumatic and intermittent fever. They differ from other fevers not only by being neither contagious nor infectious but also by their readiness to return, while a single attack of any of the others furnishes a guarantee, and often a complete guarantee, against its recurrence. In addition to these peculiarities, the fevers of which I have now to speak are characterised by running a certain definite course, being accompanied by certain peculiar appearances on the surface (generally rashes on the skin, whence their name of eruptive fevers); being attended each with its own peculiar dangers, and all having a tendency to what is termed epidemic prevalence; that is to say to occur one year, and without obvious cause with vastly greater frequency than in other years. =Mumps.=--It has been questioned whether that painful but not dangerous ailment the _mumps_, ought or ought not to be classed with these fevers. I think it should, for it is contagious, infectious, runs a fairly definite course, is attended with invariable external appearances, often prevails epidemically, and one attack preserves in most instances from a second. It very seldom befalls children under seven years of age, and is more frequent in early youth than in childhood. It sets in with the ordinary symptoms of a cold, which are followed in about twenty-four hours by stiffness of the neck, and pain about the lower jaw, which is increased by speaking or swallowing. At the same time a swelling appears, sometimes on one side sometimes on both of the lower jaw, and increases very rapidly so as to occasion great disfigurement of the face. The swelling goes on to increase, and to become more tense, attended with more head-ache, fever, and discomfort for some forty-eight hours, but then it begins to lessen, and the general illness subsides rapidly, though the enlarged gland, for that is the cause of the swelling, sometimes does not return to its natural size for a week, ten days, or more; and now and then, though very rarely, an abscess forms, which is both tedious and troublesome. The treatment suitable for a severe common cold, together with the constant application of a warm poultice to the swollen gland, is all that is usually required, though the doctor's help is often needed to relieve the suffering which for the first day or two in many instances attends the ailment. =Typhoid Fever.=--There is no question as to the place which should be occupied by typhoid fever, smallpox, measles, and scarlatina, for all belong to the class of eruptive fevers. They are all specific diseases, each due to its own peculiar poison, and not capable of being produced by any mere unsanitary conditions, though such may aggravate their severity and facilitate their spread.