around these that the protoplasm of the segmenting parasite arranges itself to form the spherules (Fig. 2, b, c). The vesicular character of the nucleus does not usually appear in the spherules until after these have become free in the liquor sanguinis (Fig. 2, d).
The haemozoin particles, so characteristic of the malaria germ, occur as black or very dark-red dust-like specks, coarse grains, or short rods, either isolated or aggregated into larger or smaller, more or less dense clumps. Until the concentration of haemozoin which precedes the formation of spherules takes place the particles are scattered, being located principally in the outer zone, or ectosarc, of the parasite. Apparently so long as the nucleus remains entire the haemozoin is peripheral; when segmentation occurs in the nucleus the haemozoin becomes central.
Such is a brief account of the cycle and structure of one phase of the parasite. From it we may understand how the parasite maintains itself and multiplies inside the human body. It does not explain, however, the two other important biological features which analogy and observation clearly indicate namely, its latency in, and its life outside, the human body.
EXTRACORPOREAL OR MOSQUITO CYCLE
As it is unreasonable to suppose that an organism which propagates so actively in the human body has no opportunity, either by passing from one host to another or in other ways, of continuing its species, we are forced to conclude that some provision must exist in the economy of the parasite that enables it to leave and enter successive hosts. The problems suggested by this consideration are first, how does the malaria parasite leave the human body; second, what is its life when temporarily outside the human body; and, third, how does the parasite re-enter the human body?
The flagellated body.—When fresh malarial blood is examined some time after it has been mounted as a wet preparation, it is no unusual thing to see
