584 PIROPLASMA BOVIS 



in the fresh blood of cattle suffering from Texas fever as a pair of 

 small, pale bodies, each one pear-shaped and touching the other, or 

 directed toward each other with their narrow-pointed ends. They 

 vary in size in different blood corpuscles, but the two forming a pair 

 are generally fairly equal. They are about 2 to 4 micra long and 1.5 

 to 2 micra wide at the broader ends. The pointed ends touch or 

 nearly touch each other and the axes of the two bodies form a varying 

 angle; they may be almost parallel or they may form a straight line, 

 and they may show any intermediate stage between these two extremes. 

 The piroplasmata are of a homogeneous not granular appearance, 

 and they are well differentiated from the stroma of the red blood 

 corpuscles in which they are found. The smaller forms are generally 

 perfectly homogeneous, the larger pear-shaped bodies often show at 

 the periphery of the large end a small, highly refractive, somewhat 

 darker round body of 0.1 to 0.2 micron in diameter, and also at or 

 near the centre of the large end a round or oval body of 0.5 to 1 micron 

 in diameter. Sometimes the piroplasmata in fresh blood show ameboid 

 motion with a change in the contour of their body, but without the 

 formation of any well-marked pseudopodia. Dead or dying organisms 

 lose the pear shape and assume a round outline. If stained cover- 

 glass or slide preparations are made from blood containing piro- 

 plasmata the alkaline anilin stain is seen to have been taken 

 generally more intensely at the margin than in the interior. Not all 

 parasites show the pear shape or occur in pairs; many are single, 

 round, oval, or irregular. 



According to Smith and Kilbourne, usually only 1 per cent, of 

 the erythrocytes are infected, but shortly before death the number 

 of infected corpuscles may be from 5 to 10 per cent. As the fever 

 disappears the parasites likewise disappear from the blood. If 

 the animal dies the blood in the capillaries of the internal organs 

 often shows an enormous infection. The piroplasmata are most 

 numerous in the kidneys (in 50 to 80 per cent, of the red blood cor- 

 puscles), and after them in the liver and spleen, and they are also 

 found free in these organs between the red corpuscles. A few hours 

 after the death of their host the parasites evidently in consequence 

 of degenerative changes lose the pear shape and assume a round 

 form. These degenerative or involution forms, however, are probably 

 not dead parasites, since such blood retains its infective character, 

 and since blood infected with piroplasma and obtained under aseptic 

 conditions may remain virulent after a stay of sixty days in the 

 refrigerator. In the incubator at 37 C. such blood remains virulent 

 for only about one week. Smith and Kilbourne have also described 

 coccus-like bodies, measuring from 0.2 to 0.5 micron, in 5 to 50 per 

 cent, of the red blood corpuscles in the mild autumnal form of the 

 disease in Texas cattle. These bodies can generally not be seen 

 unstained, but only after treatment with methylene-blue solution. 

 They are looked upon by the investigators named as a form in the 



