First. Cases occur in close relation with cases of intermittent fever in populations similarly exposed to malaria, and at the same periods of the year.
Second. The two forms of disease are readily convertible, the one with the other.
In non-tropical countries remittent fever cannot be regarded as the natural type of malarial fevers. At least, it may be affirmed that the proportion of cases which begin as remittent attacks is so small that we are warranted in looking upon them as departures from type. In the United States army during the years 1861-66, inclusive, there occurred 286,490 cases of remittent fever. The fatal cases were 3853, being a mortality-rate of 13,450 per 1,000,000 cases. By comparing these statistics with those of intermittent fever recorded in a previous section it will be found that remittent fever is more than twelve times as fatal to life as the simple intermittent forms.
If we accept this view of the pathology of remittent fever, it is of interest to the sanitarian or practitioner to endeavor to arrive at the causes which occasion these departures from type. Some of these are undoubtedly extraneous to the system, and relate wholly to circumstances affecting the malarial poison as a disease-producing agent. Increased quantity of malaria is well understood to enlarge the ratio of remittent cases. There is also strong presumptive evidence supporting the hypothesis that different annual crops of malaria vary in respect to the noxious qualities of this agent. The same presumption relates to all crops produced in certain localities as contrasted with others. Other causes which determine remittent rather than intermittent attacks are personal to patients. They may be classed as follows:
First. Unusual personal receptivity or impressibility to malaria may exist, either because of some constitutional idiosyncrasy or of some state the system at the time of exposure.
Second. Want of timely medical treatment or of proper medical treatment may convert intermittents into remittents.
Third. The rapid occurrence of secondary blood infections, extraordinary in character or amount, may cause the fever to be continuous.
Fourth. The existence of complications, inflammatory in their nature, may change intermittent into remittent attacks.
However various or complex the causes may be which operate to convert intermittent attacks into remittent forms of fever, each one must be supposed to act by disturbing the functions of those centres which preside over the normal physiological and chemical changes of the system.
SYMPTOMS AND DIAGNOSIS.—Attacks of remittent fever are, as a rule, more abrupt in their advent than intermittents. When prodromic symptoms exist, they are similar to those which precede ordinary cases of ague.