=Acute Constitutional Diseases.=--It still remains for us to glance rapidly at the characters of the _acute constitutional diseases_, all of which belong, as has already been stated, to the class of fevers. Of them all but two are contagious--that is to say, are capable of being communicated directly from person to person. They are likewise infectious, or, in other words, articles of bedding or clothes which have been worn by the sick, retain a something--an exhalation from the breath, an emanation from the skin, or a secretion from the bowels--which may reproduce the same disease in a person previously healthy. To this contagious and infectious property there are two exceptions; the one is furnished by acute rheumatism, or rheumatic fever, the other by intermittent fever, or ague. =Rheumatic Fever.=--The main features of _rheumatic fever_ are the same at all ages. Fever, pain in the limbs, swelling of the joints, sweats unattended by that relief which usually accompanies abundant action of the skin in fevers, are its characteristics. In the child all these symptoms are usually less even than in the adult. The swelling of the joints in particular is less considerable, and both the pain and the swelling are apt to wander from one to another joint, or to a different limb, instead of remaining fixed as they do in the grown person for several days in the same joint, even though fresh joints may be implicated in the course of the disease. These circumstances tend to make people look on rheumatic fever in the child too often as a comparatively trivial ailment; and this not only because the suffering which attends the disease is slighter, but because its duration is also shorter. But there is one fact which forbids this low estimate of its importance, and that is the great tendency to affection of the heart even in cases of comparatively mild rheumatism in the child; while in the grown person there is a direct relation between the general severity of the rheumatic symptoms and the liability of the heart to be involved. I have already stated that nine out of ten of all cases of heart disease in early life, not due to original malformation, are of rheumatic origin, and further that heart disease comes on in the course of four out of five cases of rheumatic fever in the child, slight as well as severe. It seldom occurs before the third or fourth day of the illness, so that if parents take the alarm at the very outset, it is usually though not invariably possible for the doctor by judicious treatment to anticipate and to prevent its occurrence, or at any rate greatly to control its progress.