The myocardium appears as if boiled, the spleen is invariably hypertrophied and two or three times as large as in the normal state.
The kidneys are violet in colour and congested, and the adipose layer surrounding the kidney is infiltrated with a yellowish serosity. The urine may present a variety of tints, derived from hæmoglobin. The liver is often engorged with blood and the gall bladder always distended.
When convalescence sets in, icterus appears; but it is a special kind of icterus, depending on changes in the hæmoglobin—in fact, a hæmaphæic icterus. Histological examination of the blood furnishes the explanation of the disease by revealing the presence of the parasite.
Fig. 196.—Slow formation of free germs. 1, Pear-shaped organisms with large chromatic element and a flagellum; 2, newly-developed round cell without chromatic element; 3, 4 and 5, formation of the chromatic elements; 6, the germs about to escape; 7, the germs freed. (After Lignières.)
Pathogeny. The parasite is the Piroplasma bigeminum, which is easily demonstrated by drying the blood, fixing it and staining with very weak methylene blue. The blood is light in colour and pale, and the serum is tinted by the dissolved hæmoglobin. The blood corpuscles diminish in number with extreme rapidity while the parasites are developing, and in twenty-four or forty-eight hours may fall from some six millions and a half, the normal number, to one million or even to two or three hundred thousand red blood corpuscles per cubic millimètre.
Fig. 197.—Rapid formation of free germs. 1, Newly-developed round parasite without distinct germs; 2, round parasite with two germs; 3, the germs approaching the surface and undergoing development; 4, the germs beginning to grow outwards preparatory to forming new round parasites; 5, the process previously noted is becoming more marked; the protoplasm of the cell is undergoing degeneration, and scarcely stains at all; 6, round parasites. This completes the cycle. These parasites (6) are similar to (1). (After Lignières.)
This destruction is due to the action of the piroplasmata, as may be shown by staining with a ·5 per cent. methylene blue or carbolised thionine. These parasites usually assume a simple pyriform shape, and two or three may be found in one blood corpuscle. The number of parasites and infected blood corpuscles is generally in direct ratio to the intensity of the infection. These parasites are found throughout the blood, but principally in that of the spleen, kidneys, and mesenteric veins. They are only abundant whilst the temperature is rising or at the moment when it reaches its highest point, and they often disappear before death or convalescence.
The pyriform shape is only temporary, and corresponds to the acute phase of the disease, but the parasite assumes the round form as soon as convalescence sets in. This round form gives birth to one, two or three spherical spores, which are set free in the plasma after the destruction of the maternal protoplasm, and are able after transference to a fresh red blood corpuscle to again assume the pyriform shape peculiar to the grave forms of disease.