THE CHROMATIN MASSES OF PIROPLASMA BIGEMINUM. 299 



II. Methods. 



The blood-smear examined had been fixed and stained by 

 the Romanowsky method. The resulting* film was a thin, 

 even, and good one, and was covered and mounted in Canada- 

 balsam. The stain of the host-cells (red blood-corpuscles) 

 was somewhat faint, which was afterwards found to be a 

 distinct advantage, but the parasites were still perfectly well 

 stained, and exhibited the red or purplish-red colour in the 

 chromatin and blue in the cytoplasm characteristic of the 

 Romanowsky coloration. 



In order to eliminate, as far as possible, sources of error 

 incidental to stained preparations — errors more especially 

 applicable, however, to the shape and structure of the cyto- 

 plasm of the parasite — the slide was examined under various 

 kinds of illumination. These, in brief, were — first, critical 

 illumination, using as a source of light the sharp edge of a 

 paraffin flume ; second, monochromatic light (green or 

 yellowish-green was best) ; and thirdly, less critical illumina- 

 tion from a Welsbach burner or an electric lamp. The last 

 mentioned should, on the whole, be rejected as somewhat 

 untrustworthy and uncomfortable in a research of this kind, 

 where so much depends on the correct determination of the 

 colour of the chromatin masses. The monochromatic light is 

 comfortable and useful for structural detail, but a source of 

 white light, such as is obtained from a parafiin flame, is 

 necessary for the determination of colour, especially of the 

 looser chromatin. In all cases, however, the chromatin could 

 be distinguished, either absolutely or relatively, from the 

 cytoplasm of the parasite, but with very bright (white) 

 sources of light, the relative sizes of the chromatin masses to 

 each other were sometimes misleading, and there was, in 

 such cases, a lack of finer detail. Wrong impressions were 

 also apt to be obtained with the very powerful sources of 

 light, concerning the size and condition of the vacuoles 

 mentioned hereafter. Daylight was also used when possible 

 (winter). 



