Soon after Laveran's discovery the question arose whether there was only one parasite for all cases or whether different species were to be differentiated?

It seems to me that we may consider this question answered, even though a considerable number of observers, with Laveran at their head, still hold to the unity of the parasites.

Referring to my monograph for more minute details in regard to the arguments on both sides of the question, we will content ourselves here with only those points which determine us in defending the multiplicity of the malarial parasites. These are:

1. The morphologic differences of the parasites occurring in the different types of fever. 2. The results of inoculation, which show, with the exception of a few experiments that are not above criticism, a similarity of parasite and type of fever in the source from which the inoculable blood was taken and the person inoculated. 3. The unchangeableness of the parasites in any single case, provided no new infection takes place. 4. The differences in the parasites and the types of fever according to the season and the geographic location.

1. The morphologic differences between the parasites in malarial fevers of different types were first demonstrated by Golgi. For the further development of this subject we have to thank the investigation of Marchiafava, Celli, Canalis, and Bignami. A detailed description of the peculiarities of the different species will be given later.

2. We refer to Table I, which shows 35 experimental blood inoculations. Of these, the first two of Gerhardt's are not fully available for our purpose, since no attention was bestowed on the parasites ; yet even here it is to be remarked that the same type of fever occurred in the inoculated as existed in the person from whom the blood was taken. Of the other 33 experiments, in 31, the parasites found in the person inoculated were proved completely identical with those in the source. In only two cases (Nos. 3 and 4) was the result different. In these the blood of the person inoculated showed parasites of the second group, while in the person from whom the blood was taken only quartan parasites were discovered. Yet we have in another place shown, and the investigators in question have confessed, that both these experiments are not above criticism, and cannot, therefore, be considered as very convincing.

In all other instances the result supports the assumption that the different forms of parasites are to be regarded as species which are unchangeable and cannot be transformed one into another.

Moreover, if we compare the types of fever occurring in the person from whom the blood was taken and in the person inoculated, we find, omitting the two questionable experiments, Nos. 3 and 4, that that type of fever was always obtained which was to be expected from the species of parasite injected.

In 22 cases the type of fever in the person inoculated was identical with that in the source; in four experiments (Nos. 17, 19, 20, and 22) a new type was found in the person inoculated. Yet we can readily show that there is here only an apparent contradiction, for all these cases showed tertian parasites and a change between tertian and quotidian fever. It is now generally recognized that tertian parasites have a great inclination to cause quotidian fever, by a doubling of the generation (as a matter of fact, a double tertian). Accordingly, we frequently see in patients with ordinary tertian alternations between these two types. This has even taken place in cases produced experimentally. In cases No. 32 to 35 the type did not reach full development in the person inoculated, since the fever was at once treated with quinin.

Inoculation experiments show, therefore, that the types of fever go over into one another, even as little as the species of parasites, and that a change of fever type takes place only within definite limits, which are measured by the biologic relations of the parasite.

Table I.-Experimental Inoculation Of Malaria

Table II shows the relations between the varieties of parasites and the different types of fever.

3. Blood examinations continued through weeks and months on malarial patients exposed to no new infection showed that the repeatedly renewed generations of parasites always belonged to the same species. Such investigations were carried on especially by Calanclruccio and di Mattei. For instance, in the case of a triple quartan, the blood was examined daily for months and always showed only quartan parasites; in two patients showing crescents the blood was examined for two and six months respectively and no other parasites than those of the second group found.

* In cases 26-31 attempts were made to immunize the person inoculated by means of different sera, and in some of these experiments, as a consequence, no attention was paid to the type of fever.

Livio Vincenzi observed for months several cases of infection with parasites of the second group without seeing any forms other than the small ameboid ones.

Similar experiences, even if not extending over such a long period, may be had by any one who is occupied with the study of malarial blood.

It need scarcely be mentioned that the parasites do not modify their forms even when the patient changes his place of habitation. I see frequently, in Vienna, patients coming from the severe malarial regions of the south infected with parasites of the second group. In spite of a long sojourn on a foreign soil free from malaria these parasites, which are never observed autochthonously in Vienna, do not change their form, but remain the same for weeks and months.

We cannot, therefore, attribute an influence in the transformation of the parasitic forms to the climate, or even to the individual constitution, as Laveran insists.

4. In reference to the difference in the parasites and the types of fever according to the season, we find that the parasites of the first group (especially those of the common tertian), with their typical intermittent fever, play their role in the spring, and that the parasites of the second and their accompanying fever appear as a primary infection in summer and autumn.