This is the most frequent fever of the temperate zone. Among my 143 cases, 88 were tertian; among 71 observed by me in Vienna, 61 were tertian; among 72 in Dalmatia and Croatia, 27 were tertian. From these statistics we can see to what an extent this form may predominate in mild malarial regions, and what a secondary place it may occupy in severe fever regions.*

The type of fever depends on whether one or two generations of parasites are present in the blood. In the first case, the type will correspond to 101010101; in the second, to 111111111, or quotidian. In the second case we have, therefore, a double tertian. This doubling of the tertian fever is extremely frequent-much more frequent than the doubling of the quartan fever previously described. Among my 88 cases of tertian fever 43 were doubled; in other words, almost half the cases.

The existence of a double tertian may often be recognized from the fever curve in that the paroxysms of the different series may differ in intensity or occur at different times in the day. As is well known, the ancient writers recognized and properly described this doubling. Much more rarely the doubling occurs in such a way that two paroxysms take place every third day. The anticipating type is frequent, the postponing less so. The latter arises usually as the result of therapy. In regard to the description of the paroxysms, what was said in relation to quartan may be repeated here.**

The curve in tertian usually rises uninterruptedly and falls again in the same manner. Yet it may happen that after a slight fall a new rise appears before the final decline takes place. In this way the duration of a paroxysm may be prolonged. This usually lasts from six or eight to twelve (rarely only four) hours, but by this complication it may be lengthened out to twenty four or thirty six hours and even more (Figs. 24 and 25). In these cases it occasionally happens that a chill occurs before the second rise, making twin paroxysms, caused by two very closely related generations of parasites.

* Still I must mention that these figures require a correction, inasmuch as the Vienna cases were drawn from all seasons of the year, while the southern ones were limited to the months August and September-in other words, times at which the fevers of the second group are especially predominant.

** It was scarcely correct when Galen said: " Tertianam quidem a quartana qui, primo statim die, nescit distinguere,- neque ommino medicus est." Though by means of the microscope, we are to day in a position to justify Galen's requirements.

Fig. 22.-Simple Tertian (Anticipating)

Fig. 23.-Simple Tertian (Anticipating)

Fig. 24.-Simple Tertian.

Fig. 25.-Simple Tertian and Prolonged Paroxysms.

By the prolongation of a paroxysm in double tertian it may happen that the beginning of a new paroxysm falls within the fever period of the preceding one; we then speak of subintrant benign tertian. If more than two generations of parasites are present,-in other words, if the paroxysms run together not on account of prolongation, but on account of the multiplication of different generations, though this is rare,-we have what we designate as subcon tinued benign tertian. (See Fig. 28.)

Irregular febrile movements are sometimes observed, though not frequently; they occur especially at the beginning of the infection.

Change of type is common, though limited to the types just described. Quartan type, I repeat, does not alternate with tertian without a new infection. The change of type is seen most frequently in relapses, in that, for instance, during the primary disease, we see simple tertian, during the relapse,-whether this occurs after treatment with quinin or spontaneous recovery,-a double tertian type, or vice versa. In other cases a gradually increasing curve developing on the days between the paroxysms announces the doubling. The reverse-the falling out of a generation-is not infrequently seen in cases of incomplete treatment.

Recovery occurs promptly under quinin, and though the first paroxysm after its administration may not be completely prevented, it is usually modified and lessened in intensity. With proper treatment a second paroxysm is scarcely ever seen, yet when the quinin is not continued sufficiently long, relapses are frequent. These occur usually two or three weeks after the last paroxysm.

Mixed Fevers

Simultaneous infection with quartan and tertian parasites is, at least in our experience, a rare occurrence. It is evident that the resulting fever curve would be no simple intermittent. On the contrary, we would see, according to the relative ages of the different generations of parasites and according to their numbers, marked deviations in the shape of intermittent, alternating with continued or subintrant, fever.

Fig. 26.-Double Tertian.

Fig. 27.-Double Tertian with Change of Type.