114 



FALLACIES AXD PrzZLES IN IlLOOD EXAMINATION 



■ Blouing 

 paper " fallacy 



Autogcnetic 

 fallacies 



Vacuoles 



happeneil, luiiiicly, that the same piece of blotting paper used to dry a stained film of 

 fowl's blood had been used to blot the other film and the corpuscles had been transferred 

 from the paper to the slide. I have known of cases in which parasites were transferred 

 in a similar way, so the need of care is obvious. Fragments of stained epithelium and 

 stain deposits often spread beyond the marf^in of any red cell on which they may lie, 

 and may be troublesome, though focussing helps to decide. 



On the whole, however, care and a little experience will soon do away with the 

 fallacies and puzzles belonging to Class I., and with a caution as to avoiding calling 

 dirt or skin pigment, melanin, which latter never occurs free, remembering that cocci 

 and bacteria get into blood and that there are sometimes strange flaws and cracks in 

 glass which may retain a stain, we may pass to the consideration of the second group. 



This it is best to consider under two headings : — • 



1. Those found in fresh blood. 



2. Those present in stained preparations. 



The former, so far as fallacies are concerned, are tlie more difficult, the latter, 

 I think, contain most of the puzzles. 



1. Ordinary crenations of the red cells do not as a rule cause any diflBculty (Plate V., 

 fig. 2), but sometimes they present a hyaline appearance and look as if situated in the 

 erythrocytes. Careful focussing soon makes their real nature apparent, for they have no 

 defined outline and change from dark to light or reversely as one alters the focus. In 

 this way they can be readily distinguished from a malaria ring-form, a piroplasm 

 or a spirochaBtal granule or body, the three things which they are most apt to resemble. 



Distorted red cells have been mistaken for malarial crescents, but the absence of 

 pigment should make things clear. I believe a red cell containing a half-grown benign 

 tertian parasite can rupture, or be ruptured, prematurely, and the amoeboid processes 

 of the parasite be severed and roll up into little protoplasmic masses in the blood. 

 These are at first puzzling, but the presence of dancing particles of pigment is a sure 

 guide to their origin, and fragments of the broken host-cell can sometimes be seen in 

 their vicinity. Vacuoles are always mentioned as specially diflBcult, and sometimes they, 

 and also a retraction of the haemoglobin from the edge of an erythrocyte, cause trouble, 

 more especially in malaria examination. 



In distinguishing a vacuole from a young malarial parasite, a piroplasm or a spirochaetal 

 inclusion and of the three the last is the most difficult to differentiate, the following 

 points should be considered : — 



(i) Vacuoles usually have well-defined, clear-cut margins, while the periphery of a 

 parasite melts, as it were, into the haemoglobin of the host-cell (Plate V., fig. 3). 



(ii) Although a vacuole may change in shape it never shows true amccboid 

 movement. The slight alterations of shape which may occur in its contour, however, 

 must not be overlooked. 



(iii) A vacuole never shows pigment or any appearance suggestive of granules m its 

 interior or projections from the vacuoloid area. 



(iv) A vacuole is clear, with no "ground glass" aspect. It is highly refractive and, 

 on focussing up and down, seems to spread and contract in a characteristic fashion. 



(v) Vacuoles never stain as a whole, though there may be deposits of colour rouml 

 their margins. 



Splits or cracks in red cells are easily recognised and only require mention, but 

 one of the most difficult of all blood appearances is furnished by areas devoid of 

 haemoglobin, also called "eye spots," "spherical gaps," "hyaline bodies," "nuclear 



