By chronic malarial infection we understand one continuing for months. This continuance does not depend on reinfection, but on an obstinate persistence of the virus. From one point of view malarial infections may be divided into acute and chronic, depending on whether the infection ceases in a short or continues for a long time, yet this division lacks a rational and sharply cut basis, and we have, consequently, made use of the etiologic classification. Still, practical reasons demand that malarial infections be considered for a moment from this standpoint, in order to call attention to certain elements which might otherwise escape observation.

Inasmuch as cases with one or several relapses are more frequent than those which cease after a shorter or longer series of paroxysms, we might say that the majority of malarial infections show a chronic character. Yet to designate as chronic every case which showed within two to four weeks a relapse would be of no practical value; therefore we must insist that the symptoms of the infection continue for months.

Without specific therapy, the great majority of malarial cases would be chronic in this latter sense, though with it the cases are limited to a relatively small number. The malarial infections caused by the first group of parasites are comparatively seldom chronic, especially when rational treatment and the proper hygienic measures have been employed, yet sometimes, in spite of proper treatment, good nourishment, healthful dwelling place, etc., they relapse for months and months-in other words, become chronic. This is true of quartan much more frequently than of tertian fever.

The parasites of the second group constitute the principal contingent in chronic infections. The resistance shown by certain developmental phases of these parasites to quinin, on account of which the infection becomes chronic, will be discussed in the sections on Pathogenesis and Therapy.

Though we usually succeed, by means of quinin and proper sanitary regulations, in preventing a relapse, we frequently fail to get rid of all the organisms. In this guerrilla warfare the therapy is unable to reach the enemy intrenched in the parenchymatous organs, though it is usually successful when the troops come out into the open field of the blood vessels. It is, therefore, evident that chronic cases are much more frequent in malarial regions where parasites of the second group are endemic than in localities where only parasites of the first group exist.

The parasites of the second group become active in the summer and autumn months. From these months, therefore, date the majority of chronic infections. The patient-supposing the case to be a soldier in a colony infected with malaria -is, for instance, in August, brought to the hospital on account of a typhoid sub continued. After eight to ten days he is convalescent, though still very pale, anemic, weak, nervous, and showing a splenic tumor. He recuperates quickly and is about to leave the hospital, when, on the last day, he manifests a severe paroxysm. The paroxysms then repeat themselves, following a tertian type, until interrupted by quinin. The patient is again anemic, the splenic tumor somewhat enlarged, etc. Recuperation now requires a longer time, and has probably not progressed very far when another relapse occurs, and so until late in the winter; more than that, we sometimes find the patient still in the hospital the subsequent spring. He is eventually given permission to return home. He arrives at home in a pitiable condition; his relatives remark the "burnt up" appearance, which is nothing else than the ashy melanosis of a chronic malaria . He gradually gains strength and considers himself almost entirely well, when one day an outbreak of blackwater fever occurs, or he falls into a comatose condition which gives the physician much difficulty in the diagnosis. The patient may succumb to this attack, or he may recover and remain entirely well, without symptoms of malaria , for the remainder of his life. In this fashion or similarly run the majority of cases which we have in mind.

In order to diagnose chronic malaria the following clinical symptoms must be present: 1. Occasionally recurring paroxysms of malaria for months (relapses); these may be normal or latent. 2. A certain degree of anemia. 3. Enlargement of the spleen and eventually enlargement of the liver. 4. The same species of parasites in the blood throughout the whole period. 5. General characteristic appearance.

In regard to the relapses, we have little to add to what has been said in the previous section. They are frequently only suggested, manifest no chill, and the patients often have no knowledge of the fact that they are passing through a fever. Moreover, people with chronic malaria are frequently so little sensitive to elevations of temperature that they fail to remark even high ones. Patients presenting all the symptoms of chronic infections sometimes absolutely assert that they have never suffered from fever. Such assertions are to be regarded with the greatest skepticism, and from my own frequent experiences are to be credited only when the temperature was taken regularly. The relapse may be latent-in fact, it is especially in chronic malaria that this manifestation occurs. Finally it must not be forgotten that the relapse may be pernicious, and that it is the chronic infection which oftenest gives rise to pernicious symptoms (for further details see Catrin).

The anemia may be of varying intensity or even entirely wanting. This last happens when the relapses take place at long intervals from one another, when during the relapses there is no great destruction of red blood corpuscles, and when the blood making organs possess a productive power capable of covering the loss in a short time. As a rule, only mild grades of anemia are seen in cases of chronic infection with parasites of the first group.