The clinical symptoms are often sufficient to determine positively the infection. This applies especially to the strictly intermittent fevers of tertian, quartan, or biquartan type, since there is no other disease that produces similarly recurring paroxysms for any length of time. Yet when we come to quotidian fever, difficulties begin to appear. Although it is the rule for malarial paroxysms to occur between midnight and midday, while other daily recurring fevers (for instance, hectic fever) choose the evening hours, this rule has so many exceptions that it would be dangerous to make a diagnosis from it. Septicopyemic fevers, like malarial paroxysms, frequently occur in the forenoon hours, and in phthisis a "typus inversus" is not infrequently seen. Still less do the continued or subcontinued fevers lend themselves to a diagnosis; on the contrary, it is exactly these which produce the greatest confusion. In regard to the paroxysm, we must remember that the three stages are usually developed in infections with parasites of the first group, and that the chill often fails in infections with the second group.
It is worth while insisting again that the thermometer is the only means of recognizing the existence of fever, and especially of diagnosing the type. The assertions of patients are entirely worthless, since subjective sensations are inaccurate. To determine the type it is necessary to allow several days to pass without specific modification, in the mean time taking the temperature regularly. Naturally this is to be done only when thereby no injury results to the patient.
Besides the typically recurring fever, there are typical repetitions of other symptoms, as pain, paralysis, abnormalities in secretion, etc., that may assist in the diagnosis of latent malaria ; still it must be remembered that such repetitions occur apart from malaria, and that neuralgias especially intermit from other causes. In such a case it is well to bear in mind that latent fevers usually occur in individuals who have suffered before from malaria .
The splenic tumor is an important diagnostic characteristic. It is very rarely entirely wanting. Its presence confirms the diagnosis, yet it is not pathognomonic, since splenic tumors occur in most other infectious diseases, for instance, typhoid fever, miliary tuberculosis, and sepsis.
The large hard chronic splenic tumor may be produced by even more conditions, so that it signifies but little in malarial cachexia. In my experience splenic pain is of very subordinate value in diagnosis.
Herpes is significant, inasmuch as it occurs frequently in malaria , and but rarely in other conditions that might come into consideration, as typhoid fever, tuberculous meningitis, and miliary tuberculosis. Still, it is not peculiar to malaria, since it is seen in many other infections, as the ephemera, acute gastritis, rheumatism, colds, influenza, etc.
Urticaria is still less characteristic. Roseola is quite negatively diagnostic. Only very isolated cases of malaria with roseola have been reported. Other symptoms are much less characteristic of malaria, so that we will refrain from repeating them.
In concrete cases, other data, like the anamnesis and the "genius epidemicus loci," must be taken into consideration. In pernicious cases the fact that the patient has repeatedly suffered from malaria is of value, though it by no means absolves the physician from excluding other diseases in every intelligent way.
In places where malaria is endemic it is always before the eyes of the physician, especially in summer and autumn, while in regions free from the disease it is the last thing thought of, except when dealing with a patient who has come from a malarial district.
There is, therefore, in malarial regions, a decided tendency to pronounce every kind of an infection that is at all indefinite malaria , and this gives rise to many errors. With his mind constantly on the proteiform specter lurking hic et ubique, the physician readily follows it, since it facilitates diagnostic difficulties and gives him a ready diagnosis applicable to the worst cases.
Though we readily agree with Baccelli that the eye of the clinician should always be able to recognize malaria , even in its most grotesque garb, we must confess that only a very small number of physicians have the good fortune to possess a "clinical eye" that can be relied upon. For the majority, therefore, Laveran's discovery acts as an inestimable talisman.
Under certain circumstances the diagnosis ex juvantibus is of value. If a fever persistent for a long time is rapidly cured by quinin, there is a certain amount of probability that it was malaria . If the fever was strictly intermittent in type, the probability becomes almost certainty. Still, it would be extremely silly to pronounce every case malaria, whether or not it showed a temperature, simply because improvement or recovery followed quinin. Is it possible to designate it otherwise when a surgeon diagnoses as malaria a hemorrhage from the stump occurring several days after an operation for carcinoma of the tongue, and ceasing after the exhibition of quinin, simply because the individual suffered years before from malaria and the hemorrhage did not recur after a couple of grams of quinin?
The literature swarms with similar examples. Still, in contrast to this, the principle may be enunciated that there is no malaria when no temporary or absolute effect is produced on the temperature after several days' administration of quinin in proper doses. Laveran affirms that a continuation of the fever after the fourth day, in spite of the daily exhibition of 1.5 to 2.0 quinin, almost absolutely excludes malaria.
Yet in very severe infections the length of time must be increased. Segard reports from Madagascar that the cases there usually begin as remittent or continued, and take on a tertian type only after six or seven days, and he asserts that quinin exercises but little influence during the primary stage. This simple and important rule is frequently forgotten, and it would not be at all difficult to give many instructive examples from my own experience.