Since 1893 my opinion has been that the flagella were organisms which act as intermediaries in the transition of the parasites to saprophytic conditions. I believed that the flagella represented the beginning of a life outside the human body, and that, as a result of the nutritive medium being unsuitable, these young saprophytes died.

My opinion was adopted by Manson, and developed further. He made the flagella flagellate spores ready to force their way into some cell not yet known outside the human organism, where they probably carry out the second half of their existence. The investigations of Sakharoff, according to which the flagella contain a chromatin substance, supported Manson's view.

In this regard Maccallum's discovery was of considerable value. He observed in the hematozoa of crows that the flagella bored their way into certain granulated parasites, which thereupon swelled up and moved away. He saw, though only once, the same occurrence in connection with the malarial parasites of man. Maccallum considered this to be a sexual act.

[The way in which Ross solved the problem of the nature of the flagella and' gave proof that the bodies were male elements, whose function was to fertilize female cells, a process naturally occurring in the mosquito's stomach, is considered in the supplement to this article (see p. 115).-Ed.]

We have now to consider a form of malarial parasites which differs in shape from the varieties so far mentioned, and is characterized by this difference. This is the crescent and the bodies allied to it, namely, the spindles and spheres. We classify all these forms under the one head-crescents.

The typical half moon bodies show a shape which is described in the name given them by Laveran ("corps en croissant"). They are slender, very delicate looking, strongly refractive, sometimes glistening bodies, about 8 to 10 micro long (seldom 20 micro), and 2 or 3 micro broad at the middle. They also contain pigment, though in varying amounts from a few isolated granules to large masses. This pigment is found either scattered irregularly in the organism or collected at one point, usually the center, where it is more or less thickly grouped. I have found this grouping very frequently in the form of an 8, and the final arrangement in two clumps or rows. Moreover, Babes and Gheorgiu have also observed and described this double division of the pigment.

When concentrated, the pigment is motionless; when scattered, it shows a slight trembling movement, which may be associated with a slight change of place.

The crescents possess no ameboid motion, yet show the power of gradually changing their shape.

Laveran has observed under the microscope half moons develop to spindles, ovals, and finally spheres. This change of shape is scarcely perceptible, and often requires an observation lasting several hours to see it, yet sometimes it occurs in a few minutes.

While some crescents stretch out to a spindle or cigar shape, and by the gradual equalization of their diameters become oval or spheric, others may form at the bend a sharp angle which likewise modifies considerably the half moon.

The transition of the half moon into the sphere is followed by further changes. The pigment, up to this time immotile, and forming usually a pretty regular circle within the organism, begins to show the trembling and swaying movements mentioned above. After a short while the circle is broken up and the now scattered granules tumble actively about. The protrusion of flagella soon follows.

What is the relation of the half moons to the red blood corpuscles?

Laveran considered the crescents to be free bodies swimming in the plasma, and reported in his first communication that only here and there were they to be seen attached to red blood corpuscles, from which they again separated themselves. Yet it must be added that Laveran, even in his first publication, described a fine line which, running in an arch, bound the two sides of the bow together. This fine line is nothing else than the boundary line of the red blood corpuscle, in the interior of which, as Marchiafava and Celli first recognized, the crescent develops. The blood corpuscle is, therefore, as a rule, so decolorized that its substance is scarcely perceptible, and its presence is indicated only by its refractive margin, though sometimes we see a remnant of the hemoglobin still covering the half moon. A blood corpuscle usually contains only one half moon, very rarely more than one.

The crescents, together with the spheres and ovals derived from them, are characterized by an especially sharp contour, so that the spheric bodies of the crescentic class are easily differentiated by the experienced from the spheres which constitute the adult parasites of the first group. In some instances we see a double contour, indicating that the organism possesses a membrane.

We may mention here some of the older views held as to the nature of crescents, though these have now only a historic interest.

Laveran considered the crescents and their spheres to be encysted bodies, in which, eventually, the flagella, regarded by him as a very important stage in the development of the parasite, would be formed. Councilman concluded, on account of their resistance to quinin, that they were spores. Antolisei refused to accept Councilman's view, because they contained pigment, and he looked on crescents as adult forms whose fate it was to die. Bignami and Bastianelli adopted Antolisei's opinion, and described them as sterile modified products of the ameboid parasites. Canalis believed that he observed sporu lation in the crescent, but this was not confirmed.

While the writers so far unanimously agreed that crescents originated from small ameboid parasites that were capable of breaking up into spores, Grassi and Feletti denied this and claimed that they developed from ameboid parasites which were incapable of sporu lation, and capable only of forming crescents. They consider these parasites as a particular class, and name them Laverania malarise.