The two species of the first group may be differentiated by the activity of the ameboid movement, by the size and color of the infected blood corpuscles, and, in case sporulation forms are present, by their shape, size, and the number and structure of the spores. Having recognized the species, we endeavor to find out if one or several generations are present. This is very difficult for the beginner, because he is easily confused both by the large sexual forms that have overlived the paroxysm and by slight differences between individuals of the same generation, so that he may believe all stages-in other words, innumerable generations-to be present in the blood, when, as a matter of fact, there may be only two or perhaps only one generation.
It must be remembered that we are dealing with a living organism, the phases of which show rather considerable deviations, and cannot, therefore, be reckoned according to mathematic formulas. Our conclusions, consequently, in relation to the number of generations, should be based not on isolated forms, but on large numbers in the same stage of development. These stages are reckoned, and without great difficulty, according to their approach toward sporulation (therefore, the paroxysm), from the size, the motility, and the pigmentation of the parasite. The severity of the attack is, according to Golgi, in proportion to the number of parasites.*
We proceed similarly in relation to the parasites of the second group. The determination of a mixed infection is somewhat complicated, yet in the majority of cases the difficulties are by no means insurmountable.
Let us turn, now, to a negative finding. It has happened to me, as well as to other observers (it was especially Baccelli who took up this side of the question), that parasites could not be found in spite of repeated careful blood examinations, when all the symptoms, the course of the disease, and the action of quinin pointed to malaria . These cases were rare, numbering altogether 3 among 130. In any disease a negative finding is of little significance. Moreover, in very recent malarial infections, in other words, during the first days of the disease, the parasites are sometimes missed, and this is true of even those cases experimentally produced by the injection of malarial blood.
The explanation of this is that the parasites are present in such small numbers during the first days that they are difficult to find, or that they are confined during this stage to the internal organs.
In order to arrive at a certain conclusion it is, therefore, advisable, in case the examination has proved negative, to wait for one or several paroxysms, so as to repeat the examination at especially favorable times- before the paroxysm. In these cases, too, it is possible that puncture of the spleen may be justifiable.