300 H. B. FANTHAM. 



The objectives employed were Zeiss' 2 mm, and 3 mm. 

 apochroraatics, aperture 1"40, and compensating oculars 8, 12, 

 and 18, the various combinations of these all giving, in the 

 main, precisely similar results, with little or no increase in 

 detail, for a maximum amount of detail is obtained with 

 compensating ocular 8 and 3 mm. apochromatic homogeneous 

 immersion objective. 



Lastly, it seems quite certain that relatively pale-stained 

 preparations are much to be preferred to more deeply stained 

 ones. Nuttall and Grahain-Smith (8, p. 588) lay stress on 

 tlie necessity of differentiation Avith methylated spirit after 

 coloration with comparatively dilute solutions of Giemsa's 

 stain. It seems to me probable that, in the past, the frequent 

 deep-blue staining, together with the more or less blue 

 coloration of the enclosing blood-corpuscle, usually obtained 

 by the various modifications of the Romanowsky method, 

 using strong solutions, after one quarter to half an hour's 

 staining, has perhaps obscured the finer chromatic details 

 and masked the looser chromatin in such small endoglobular 

 forms as Piroplasmata, and has also hidden the finer structural 

 details of the cytoplasm, vacuolated or otherwise. 



III. Previous Observations on the Chromatin of Piro- 



PLASMA BIQEMINUM AND P. CANIS. 



The parasite of Texas fever was discovered by Smith and 

 Kilborne, and carefully described by them in 1893 (10), 

 though they saw the parasite in 1889 and apparently "noticed 

 [it] in the spleen of a case as early as 1886" (10, p. 213). 

 Their classical monograph is perhaps, nowadays, hardly con- 

 sulted as much as it still deserves to be, though the memoir is 

 not always easy of access, unless one procures a copy direct 

 from Washington. The chief stain used by the American 

 investigators was the alkaline methylene blue of Loffler, and 

 the presence of a nucleus in the parasite is not specifically 

 meationed by them. However, there can be little doubt that 

 the nucleus, as described later by Laveran and Nicolle (3), 



