Infections caused by parasites of the second group very frequently show at the beginning a continued fever. Only after the course of several days, and then usually under the influence of quinin, does this continued change into an intermittent. I have occasionally seen the same thing occur in infections of the first group, though this is relatively rare.
In subtropical and tropical regions, in the midst of the chief foci of severe infection, it is a daily occurrence to see the primary infection begin as a continued or remittent and after a few days change to intermittent.
We are not at present sufficiently advanced to explain this occurrence in a parasitologic way. Accurate blood examinations of the initial continued, as it has been designated, will probably show the reason for it. In several observations the peripheral blood has been found during the initial continued poor in parasites.
Turning back once more, we wish again to insist that the fever paroxysm is the result of the action of the poison elaborated by the parasites on the vasomotor centers.
In the older speculations the two factors that constitute the basis of the paroxysm were sometimes properly comprehended, though again too much predominance was given to one.
Torti attributed the intermittence to a poison which, from time to time, contaminated the blood Bailly asserted " . . . L'intermittence est une disposition physiologique consistant dans l'exci tation alternative des fonctions des deux systemes nerveux, abdominal et cerebral. . . " In the same way as Bailly and Van Swie ten, Trousseau comprehended the question. He explained malaria as a "neurosis." Griesinger energetically contradicted this opinion, and with astonishing acumen insisted: "The cause of the periodicity of the fever cannot, therefore, be referred, as has frequently been done, to a predisposition of the nervous system to rhythmical vital phenomena. On the contrary, from the present state of our knowledge of the production of temperature (though this is very incomplete) it must be attributed to some periodic occurrence in the blood associated with elevation of temperature."
The severity of the paroxysms is, according to Golgi, in exact proportion to the number of parasites. Yet the peripheral blood by no means gives a proper idea of the number, since accumulations in the internal organs are very common. Moreover, the specific virulence of the parasites, as well as the power of reaction on the part of the individual, also comes into consideration.
The postmalarial secondary fever which is sometimes observed in cachectics rarely after primary infections is not very clear in its pathogenesis. It is usually slight, extends over days or possibly weeks, shows a negative blood examination, and does not react to quinin. It is possible that the anatomic lesions produced in the parenchymatous organs are responsible for it.
The change of type, a frequent phenomenon in malaria , for which previously there was no explanation, is at present attributed to the increase or diminution of the generations.
The manner in which the generations increase or decrease, though easdy comprehended in some cases, is a problem in many. It is sometimes possible to distinguish in the blood two generations of parasites-one in such small numbers as to be incapable of causing paroxysms; the other in large numbers and producing them. The first generation becomes stronger from day to day until at length capable of producing first mild, then severer, paroxysms. Whether such a generation arises through a second infection or by the separation, within the organism, of individual members from the one generation, we cannot say.
A change of type by a falling out of a series of paroxysms is the result of the death of a single generation of parasites. This disappearance of a whole generation or the greater part of it may occur either under the influence of therapy or spontaneously. In this way we frequently see a simple tertian develop from a double tertian. That quinin may kill a single generation and spare a second is due to the parasites possessing a different susceptibility for the drug, according to their age.
It was previously thought that the change of type occurred arbitrarily-in other words, that from one type any other might develop. The faculty of anticipation and postponement was employed to construct an outline showing the transition of one type into others.
The actual condition, however, is very different. The change of type takes place only under very strict rules, and anticipation and postponement scarcely come into consideration, or at most only incidentally. Naturally, these rules apply only when the infection is simple-that is, when only one species of parasites is in the blood, and a subsequent infection from the external world is excluded. Under these circumstances a continued, a tertian, or a double or simple quartan may develop from a quotidian; a quotidian or a continued from a tertian; a double quartan, a quotidian, or a continued from a quartan, but a tertian never from a quartan, or vice versa.
A difficult question is, Why in multiple infection do the parasites usually show a difference in age of about twenty four hours, or two times twenty four hours ? in other words, why do the paroxysms of two generations fall about the same time in the clay? True, this rule has many exceptions, and it occasionally happens that in double tertian, for instance, one paroxysm occurs in the morning and the other in the afternoon; yet the occurrence of the paroxysms at the same time on different days in such a great majority of cases furnishes food for reflection, because it is at present inexplicable.
Anticipation and postponement of the paroxysm are produced by the parasites developing more rapidly or more slowly than is ordinarily the rule.
For the present we must regard it as a coincidence-even though it possibly is not-that the duration of evolution of the malarial parasites is twenty four hours or a multiple of it, or, in other words, that it keeps step with our calendar day. Yet a generation may depart from this astronomic cycle and develop in a more (postponement) or less (anticipation) number of hours.