PERIOD OF INFECTION.—The period of infection is long. The disease is not in fectious during the period of incubation, but it may be so from the first appear ance of changes in the throat. The most actively-contagious period is at the height of the febrile stage: on the third, fourth, and fifth days. The infectious power then diminishes, but increases again dur ing the stage of desquamation. The period of contagion continues until the last evidences of desquamation have dis appeared. The purulent discharges from the throat, nose, and ears are capable of infecting others, and isolation should not be relaxed until they have disappeared. The conventional forty days is not too long. It should be as much longer as the condition of the skin and mucous membranes may indicate.
The causes producing "return" cases of scarlatina are thought to be the follow ing: (1) imperfect disinfection of the clothing of the first patient; (2) the re tention of the poison in the skin or throat, or most often in the discharges form the throat, nose, or ears; (3) in fection contracted before leaving the hospital by patients admitted for other diseases. J. Wright Mason (Public Health, Apr., '98).
Four thousand nine hundred and ten cases of scarlet fever collected, of which 158, upon their return home, appeared to have carried infection and to have caused 171 new cases. The greater pro portion of infection occurred during the first week, and diminished quite rapidly until the sixth. As these cases were isolated for an average period of S.3 weeks from the initial symptom, it ap pears that this period is insufficient. Of these cases, those that were isolated for more than 9 weeks conveyed less than half as much infection as the others. The so-called return cases are usually of the severe type. The source of infection may be either the nasal discharge, the discharge from the ear, or the des quamated skin. C. K. Millard (Brit. Med. Jour., Sept. 3, '9S).
Pathology.—In uncomplicated scarlet fever the lesions are confined to the skin and throat. The lesions of the skin are those of acute dermatitis. The papilla; and the stratum beneath become infil trated with fluid, while about the blood vessels there are aggregations of leuco cytes. The production of epithelium is greatly increased during the acute stages, which result later in profuse exfoliation of the superficial layers. In the later
stages in addition to this, according to Neumann, there is also a profuse devel opment of exudative cells, particularly among the ducts and follicles. These • cells easily reach the epithelial surface: a fact which accounts for the great in fectiousness of the desquamating cells.
The throat changes in uncomplicated 1 scarlet fever are catarrhal in nature, and • are an essential part of the disease. The croupous and diphtheritic membranes must be considered as complications.
Except in a very few mild cases, the throat always shows some pathological change. A catarrhal condi tion of the throat is normal to scarlet fever, but membranous exudates and gangrene are not essential to it.
The true nature of the membranous inflammation seen in scarlet fever was long a subject of discussion, which has been settled by the bacteriologist. With few exceptions, the angina of the early stages is pseudodiphtheria, that of the late stages true diphtheria. While pri mary pseudodiphtheria is a mild disease, the death-rate being rarely over 5 per cent., secondary pseudodiphtheria is very dangerous and fatal. The membrane may appear on the throat on the first or sec ond day, but it is not usually seen before the third clay. It is generally confined to the tonsils, but frequently fills the throat and naso-pharynx. It shows a tendency to invade the ears and nose and to shun the larynx. It reaches its height about the sixth or seventh day. It fre quently presents all the local character istics of diphtheria together with the general symptoms of The exciting cause of this membranous in flammation is the streptococcus pyogenes. It is occasionally associated with the staphlyococcus aureus or albus, but the streptococcus is the more commonly ob served. It occurs not only in the pseudo membrane and the tissues underneath it, but is found in the blood in large num bers. Through the agency of the toxins which it generates it is unquestionably the cause of the complications and gen eral septicTmia. The pseudomembranes which appear late in the disease are usu ally associated with the Klebs-Locffler bacillus. Diphtheria is, in the fullest sense of the word, a complication, and is not an essential symptom of scarlet fever.