In our present state of knowledge we are no more able to explain those perversions of the normal action of the physical forces of the system which occasion the phenomena of a chill than we are to explain how the altered circulation in the first steps of an inflammation is brought about. The theory which Cullen adopted is quite as explanatory and consistent as any which has been promulgated since his time. According to this, a state of spasm of the arterioles and capillaries causes the chill, while the fever is merely the rebound of functions held in abeyance during the chill.
After a variable length of time there occurs a change in these symptoms: the patient begins to remove the blankets which covered him; the face shows signs of returning circulation; the veins of the whole surface gradually fill again, apparently beyond their normal state. But the reaction goes far beyond any normal physiological state. The face becomes flushed and the eyes injected, and the patient complains of headache, thirst, dryness and heat of the surface; he will not permit any covering, and constantly shifts his place in the bed in the hope that some new position may afford him more comfort. Nausea and vomiting are commonly present. If the fever runs high, delirium is apt to occur. The thermometer seldom shows a temperature above 105°, but I have seen 106.5° recorded in the axilla in the hot stage of a paroxysm of simple intermittent fever.
The duration of the hot stage is different in different cases. According to Aitken, the mean duration is three to eight hours.
There is a very old and quite well-supported opinion, that the cold stage is shorter in the quotidian than in the tertian type, and also that the hot stage is longer in the former than in the latter. It may certainly be affirmed that in individual cases of either type there is no fixed relation between the duration of the chill and that of the hot stage.
The decline of the hot stage begins by the appearance of a gentle perspiration, limited at first to the forehead, face, and neck. This gradually extends itself over the surface and increases in quantity until the whole body is bathed in a profuse sweat. During this period the patient's symptoms, both subjective and objective, undergo wonderful mitigation, and, although this stage is usually short, it often happens that by the time it is concluded a restoration to ordinary health seems to have occurred.
The sweating stage terminates a malarial paroxysm. The intermission now begins, and lasts until the inauguration of another paroxysm. The intermission is longer or shorter accordingly, first, as the paroxysm occupies less or more time; and, second, as the interval may affect it. The interval is that period of time which reaches from the beginning of one paroxysm to the beginning of another. It therefore furnishes the basis of classification of simple intermittents into the following forms: quotidian, tertian, and quartan.
Statistics gathered from a great many sources and relating to many countries and climates indicate that quotidian intermittents are more common than tertian. It may then be assumed that the natural type of intermittents is that form characterized by diurnal paroxysms. It must be remarked, however, that if any natural law does exist establishing the quotidian as the typical form of intermittent fevers, it is very often set aside by unknown influences. In certain epidemics the tertian cases preponderate, and under all circumstances convertibility may be witnessed between the various forms.
It is probable that the statistics gathered by the medical staff of the United States Army during the late Civil War afford the most valuable data which we possess touching these points, in so far as they relate to this country. During three years of the war 724,284 cases of intermittent fever were recorded, tabulated as follows:
Quotidian, 370,401 cases, 388 deaths—equivalent to 1047 + deaths per 1,000,000 cases.
Tertian, 318,704 cases, 324 deaths—equivalent to 1007 + deaths per 1,000,000 cases.