The same reasoning applies to the case of the malarial fevers— allowance being made for the essential difference between their poi sons and that which causes relapsing fever.
They have no local lesion because their poison finds its nidus in the blood. The fever recurs for the same reason that it recurs in relapsing fever—because the nidus is renewed before the poison is eliminated from the system.
The time requisite for the exhaustion of the nidus gives to each of the specific fevers one of their distinctive features—a definite period of duration. It takes on an average about three weeks for the poison of typhoid fever to exhaust its nidus; that of typhus takes two weeks, that of relapsing fever one week. Hence the respective duration of these fevers is twenty-one, fourteen, and seven days; what special in gredient of the blood it is which forms the nidus in relapsing fever we do not know, any more than we know what it is in the intestinal glands that makes them a suitable nidus for the poison of typhoid fever, or what it is in the skin of the hairy scalp which makes it a suitable nidus for the parasite of ringworm. It is some other ingre dient which makes the blood a suitable nidus for the poison of inter mittent fever.
Recent researches seem to show that this poison, the plasmodium malari, finds its nidus in the red blood corpuscles of man. These of course are constantly being renewed; and in this fact we have a possible explanation of the quickly recurring periods of pyrexia and apyrexia which give to malarial fever its intermittent course. On
the other hand, the various changes which the plasmodium undergoes in the blood and the various forms which it assumes, render it possi ble that malarial fevers may owe their intermitting course to these changes and to the peculiarities which are special to the personal history of the poison itself. That is a point which future investiga tions will settle. What is proved is that the poison of malarial fever is a minute organism which is largely propagated in the blood dur ing the course of the maladies to which it gives rise. That is the point which concerns us at present.
It is in connection with the pathogenesis of rheumatic fever that we have been led to consider the nature and mode of action of ma laria. We believe the rheumatic poison to be malarial in nature. If it be so, it is a minute parasitic organism whose morbific action, like that of other malarial poisons, is dependent on its growth and repro duction in the system.
Like other allied poisons it is sure to require, in virtue of its para sitic nature, a special nidus for its reproduction and action. This uidus it finds in the human body. What we have now to do is to explain how a poison having such a nature and such a mode of action produces the phenomena of rheumatic fever.