(5) Smithia (França). Pear-shaped, single forms stretching across the blood corpuscle. Multiplication into four in the form of a cross. S. microti from Microtus arvalis, S. talpæ from the mole.
(6) Rossiella (Nuttall). This belongs to the family Piroplasmidæ of França. It is intracorpuscular and non-pigment forming, occurring singly, in pairs, or occasionally in fours. It is usually round and larger than Babesia. The parasite multiplies by binary fission. R. rossi in the jackal.
The genus Babesia is the best known and most important, and will be considered next.
Genus. Babesia, Starcovici, 1893.
Syn.: Pyrosoma, Smith and Kilborne, 1893; Apiosoma, Wandolleck, 1895; Piroplasma, W. H. Patton, 1895; Amœbosporidium, Bonome, 1895.
The organisms belonging to this genus are pyriform, round or amœboid. The characteristic mode of division is as follows: Just before division the parasite becomes amœboid and irregular in shape, (fig. 91, 1–5) with a compact nucleus. The latter gives off a nuclear bud. This nuclear bud divides into two by forking (fig. 91, 6, 7). The chromatin forks grow towards the surface of the body of the rounded parasite, and then two cytoplasmic buds grow out. The forking nuclear buds, which are Y-shaped, pass into the cytoplasmic outgrowths[212] (fig. 91, 8, 9). The buds gradually increase in size at the expense of the parent form until they become two pear-shaped parasites joined at their pointed ends. The connecting strand shrinks and the two daughter forms separate (fig. 91, 10–14). The pyriform parasites after having exhausted the blood corpuscle escape from it (fig. 91, 15), and seek out fresh host corpuscles, entering by the rounded, blunt end (fig. 91, 1). It is the pyriform phase of the parasite which penetrates red blood corpuscles, not rounded forms, which die if set free. The pyriform parasite, however, becomes rounded (fig. 91, 2, 3), soon after its entry into a fresh host cell. This interesting mode of division by gemmation and chromatin forking has been made diagnostic of the genus Babesia by Nuttall.[213] Rounded forms of Babesia divide by binary fission, and this direct method can also be adopted by the other forms of Babesia.
Fig. 91.—Babesia (Piroplasma) canis, life-cycle in stained preparations of infected blood of dog. (After Nuttall and Graham-Smith.)
The distribution of the chromatin in the pear-shaped Babesia, as seen in B. canis and B. bovis, is interesting. The main nuclear body consists of a karyosome surrounded by a clear area. There is also a loose (chromidial) mass of chromatin representing the remains of the chromatin forks seen during the formation of the parasite as a daughter form by gemmation. Occasionally there is a small dot or point, the so-called “blepharoplast” of Schaudinn and Lühe. This minute dot is not a flagellate blepharoplast, for there is no flagellate stage in the life-history of Babesia. These nuclear phenomena have been described by Nuttall and Graham-Smith and Christophers (1907)[214] for B. canis, by Fantham (1907)[215] for B. bovis, and by Thomson and Fantham (1913) from glucose-blood cultures of B. canis.